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NAME

       BPF-HELPERS - list of eBPF helper functions

DESCRIPTION

       The  extended  Berkeley  Packet  Filter (eBPF) subsystem consists in programs written in a
       pseudo-assembly language, then attached to one of the several  kernel  hooks  and  run  in
       reaction  of  specific  events.  This  framework differs from the older, "classic" BPF (or
       "cBPF") in several aspects, one of them being the ability to call  special  functions  (or
       "helpers")  from  within  a  program.   These  functions are restricted to a white-list of
       helpers defined in the kernel.

       These helpers are used by eBPF programs to interact with the system, or with  the  context
       in which they work. For instance, they can be used to print debugging messages, to get the
       time since the system was booted, to interact with eBPF maps,  or  to  manipulate  network
       packets.  Since there are several eBPF program types, and that they do not run in the same
       context, each program type can only call a subset of those helpers.

       Due to eBPF conventions, a helper can not have more than five arguments.

       Internally, eBPF programs  call  directly  into  the  compiled  helper  functions  without
       requiring  any  foreign-function  interface.  As  a  result, calling helpers introduces no
       overhead, thus offering excellent performance.

       This document is an attempt to list and document the helpers available to eBPF developers.
       They are sorted by chronological order (the oldest helpers in the kernel at the top).

HELPERS

       void *bpf_map_lookup_elem(struct bpf_map *map, const void *key)

              Description
                     Perform a lookup in map for an entry associated to key.

              Return Map value associated to key, or NULL if no entry was found.

       long  bpf_map_update_elem(struct  bpf_map  *map,  const  void *key, const void *value, u64
       flags)

              Description
                     Add or update the value of the entry associated to key in  map  with  value.
                     flags is one of:

                     BPF_NOEXIST
                            The entry for key must not exist in the map.

                     BPF_EXIST
                            The entry for key must already exist in the map.

                     BPF_ANY
                            No condition on the existence of the entry for key.

                     Flag  value  BPF_NOEXIST cannot be used for maps of types BPF_MAP_TYPE_ARRAY
                     or BPF_MAP_TYPE_PERCPU_ARRAY  (all elements always exist), the helper  would
                     return an error.

              Return 0 on success, or a negative error in case of failure.

       long bpf_map_delete_elem(struct bpf_map *map, const void *key)

              Description
                     Delete entry with key from map.

              Return 0 on success, or a negative error in case of failure.

       long bpf_probe_read(void *dst, u32 size, const void *unsafe_ptr)

              Description
                     For  tracing  programs,  safely attempt to read size bytes from kernel space
                     address unsafe_ptr and store the data in dst.

                     Generally, use bpf_probe_read_user() or bpf_probe_read_kernel() instead.

              Return 0 on success, or a negative error in case of failure.

       u64 bpf_ktime_get_ns(void)

              Description
                     Return the time elapsed since system boot, in nanoseconds.  Does not include
                     time the system was suspended.  See: clock_gettime(CLOCK_MONOTONIC)

              Return Current ktime.

       long bpf_trace_printk(const char *fmt, u32 fmt_size, ...)

              Description
                     This helper is a "printk()-like" facility for debugging. It prints a message
                     defined    by    format    fmt    (of     size     fmt_size)     to     file
                     /sys/kernel/debug/tracing/trace  from  DebugFS, if available. It can take up
                     to three additional u64 arguments (as an eBPF helpers, the total  number  of
                     arguments is limited to five).

                     Each  time  the helper is called, it appends a line to the trace.  Lines are
                     discarded    while    /sys/kernel/debug/tracing/trace    is    open,     use
                     /sys/kernel/debug/tracing/trace_pipe to avoid this.  The format of the trace
                     is customizable, and the exact output one will get depends  on  the  options
                     set  in  /sys/kernel/debug/tracing/trace_options  (see  also the README file
                     under the same directory). However, it usually defaults to something like:

                        telnet-470   [001] .N.. 419421.045894: 0x00000001: <formatted msg>

                     In the above:

                        · telnet is the name of the current task.

                        · 470 is the PID of the current task.

                        · 001 is the CPU number on which the task is running.

                        · In .N.., each character refers to a set of options  (whether  irqs  are
                          enabled,  scheduling  options, whether hard/softirqs are running, level
                          of preempt_disabled respectively). N means  that  TIF_NEED_RESCHED  and
                          PREEMPT_NEED_RESCHED are set.

                        · 419421.045894 is a timestamp.

                        · 0x00000001  is  a  fake  value  used by BPF for the instruction pointer
                          register.

                        · <formatted msg> is the message formatted with fmt.

                     The conversion specifiers supported by fmt are  similar,  but  more  limited
                     than  for printk(). They are %d, %i, %u, %x, %ld, %li, %lu, %lx, %lld, %lli,
                     %llu, %llx, %p, %s. No modifier (size of field, padding with  zeroes,  etc.)
                     is  available,  and the helper will return -EINVAL (but print nothing) if it
                     encounters an unknown specifier.

                     Also, note that bpf_trace_printk() is slow, and  should  only  be  used  for
                     debugging purposes. For this reason, a notice block (spanning several lines)
                     is printed to kernel logs and states that the helper should not be used "for
                     production  use" the first time this helper is used (or more precisely, when
                     trace_printk() buffers are allocated). For passing  values  to  user  space,
                     perf events should be preferred.

              Return The  number  of  bytes written to the buffer, or a negative error in case of
                     failure.

       u32 bpf_get_prandom_u32(void)

              Description
                     Get a pseudo-random number.

                     From a security point of  view,  this  helper  uses  its  own  pseudo-random
                     internal  state,  and  cannot  be  used  to  infer  the seed of other random
                     functions in the kernel. However, it is essential to note that the generator
                     used by the helper is not cryptographically secure.

              Return A random 32-bit unsigned value.

       u32 bpf_get_smp_processor_id(void)

              Description
                     Get the SMP (symmetric multiprocessing) processor id. Note that all programs
                     run with preemption disabled, which means  that  the  SMP  processor  id  is
                     stable during all the execution of the program.

              Return The SMP id of the processor running the program.

       long  bpf_skb_store_bytes(struct  sk_buff *skb, u32 offset, const void *from, u32 len, u64
       flags)

              Description
                     Store len bytes from address from into the  packet  associated  to  skb,  at
                     offset.  flags  are  a  combination  of  BPF_F_RECOMPUTE_CSUM (automatically
                     recompute  the  checksum  for  the  packet  after  storing  the  bytes)  and
                     BPF_F_INVALIDATE_HASH (set skb->hash, skb->swhash and skb->l4hash to 0).

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore, at load time, all checks  on  pointers  previously  done  by  the
                     verifier  are invalidated and must be performed again, if the helper is used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       long bpf_l3_csum_replace(struct sk_buff *skb, u32 offset, u64 from, u64 to, u64 size)

              Description
                     Recompute the layer 3 (e.g. IP) checksum for the packet associated  to  skb.
                     Computation  is incremental, so the helper must know the former value of the
                     header field that was modified (from), the new value of this field (to), and
                     the number of bytes (2 or 4) for this field, stored in size.  Alternatively,
                     it is possible to store the difference between  the  previous  and  the  new
                     values  of  the  header field in to, by setting from and size to 0. For both
                     methods, offset indicates the location of the IP checksum within the packet.

                     This helper works in combination with bpf_csum_diff(), which does not update
                     the  checksum  in-place,  but  offers  more flexibility and can handle sizes
                     larger than 2 or 4 for the checksum to update.

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore,  at  load  time,  all  checks  on pointers previously done by the
                     verifier are invalidated and must be performed again, if the helper is  used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       long bpf_l4_csum_replace(struct sk_buff *skb, u32 offset, u64 from, u64 to, u64 flags)

              Description
                     Recompute  the  layer  4  (e.g.  TCP,  UDP  or ICMP) checksum for the packet
                     associated to skb. Computation is incremental, so the helper must  know  the
                     former  value of the header field that was modified (from), the new value of
                     this field (to), and the number of bytes (2 or 4) for this field, stored  on
                     the  lowest  four  bits of flags. Alternatively, it is possible to store the
                     difference between the previous and the new values of the  header  field  in
                     to,  by  setting  from  and  the  four  lowest  bits of flags to 0. For both
                     methods, offset indicates the location of the IP checksum within the packet.
                     In addition to the size of the field, flags can be added (bitwise OR) actual
                     flags. With BPF_F_MARK_MANGLED_0, a null checksum is left untouched  (unless
                     BPF_F_MARK_ENFORCE  is  added  as well), and for updates resulting in a null
                     checksum the value is set to CSUM_MANGLED_0 instead.  Flag  BPF_F_PSEUDO_HDR
                     indicates the checksum is to be computed against a pseudo-header.

                     This helper works in combination with bpf_csum_diff(), which does not update
                     the checksum in-place, but offers more  flexibility  and  can  handle  sizes
                     larger than 2 or 4 for the checksum to update.

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore, at load time, all checks  on  pointers  previously  done  by  the
                     verifier  are invalidated and must be performed again, if the helper is used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       long bpf_tail_call(void *ctx, struct bpf_map *prog_array_map, u32 index)

              Description
                     This special helper is used to trigger a "tail call", or in other words,  to
                     jump  into another eBPF program. The same stack frame is used (but values on
                     stack and in registers for the caller are not  accessible  to  the  callee).
                     This  mechanism  allows for program chaining, either for raising the maximum
                     number of available eBPF instructions,  or  to  execute  given  programs  in
                     conditional  blocks.  For  security  reasons, there is an upper limit to the
                     number of successive tail calls that can be performed.

                     Upon call of this helper, the  program  attempts  to  jump  into  a  program
                     referenced  at  index  index  in  prog_array_map,  a  special  map  of  type
                     BPF_MAP_TYPE_PROG_ARRAY, and passes ctx, a pointer to the context.

                     If the call succeeds, the kernel immediately runs the first  instruction  of
                     the  new  program.  This is not a function call, and it never returns to the
                     previous program. If the call fails, then the helper has no effect, and  the
                     caller  continues to run its subsequent instructions. A call can fail if the
                     destination program for the jump does not exist (i.e. index is  superior  to
                     the  number  of entries in prog_array_map), or if the maximum number of tail
                     calls has been reached for this chain of programs. This limit is defined  in
                     the  kernel  by  the macro MAX_TAIL_CALL_CNT (not accessible to user space),
                     which is currently set to 32.

              Return 0 on success, or a negative error in case of failure.

       long bpf_clone_redirect(struct sk_buff *skb, u32 ifindex, u64 flags)

              Description
                     Clone and redirect the packet associated to skb to  another  net  device  of
                     index   ifindex.  Both  ingress  and  egress  interfaces  can  be  used  for
                     redirection.  The  BPF_F_INGRESS  value  in  flags  is  used  to  make   the
                     distinction  (ingress  path  is selected if the flag is present, egress path
                     otherwise).  This is the only flag supported for now.

                     In comparison  with  bpf_redirect()  helper,  bpf_clone_redirect()  has  the
                     associated  cost  of duplicating the packet buffer, but this can be executed
                     out of the eBPF program. Conversely, bpf_redirect() is more  efficient,  but
                     it  is  handled  through  an  action code where the redirection happens only
                     after the eBPF program has returned.

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore,  at  load  time,  all  checks  on pointers previously done by the
                     verifier are invalidated and must be performed again, if the helper is  used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       u64 bpf_get_current_pid_tgid(void)

              Return A  64-bit  integer containing the current tgid and pid, and created as such:
                     current_task->tgid << 32 | current_task->pid.

       u64 bpf_get_current_uid_gid(void)

              Return A 64-bit integer containing the current GID and UID, and  created  as  such:
                     current_gid << 32 | current_uid.

       long bpf_get_current_comm(void *buf, u32 size_of_buf)

              Description
                     Copy  the  comm  attribute  of the current task into buf of size_of_buf. The
                     comm attribute contains the name of the executable (excluding the path)  for
                     the current task. The size_of_buf must be strictly positive. On success, the
                     helper makes sure that the buf is NUL-terminated. On failure, it  is  filled
                     with zeroes.

              Return 0 on success, or a negative error in case of failure.

       u32 bpf_get_cgroup_classid(struct sk_buff *skb)

              Description
                     Retrieve  the  classid  for the current task, i.e. for the net_cls cgroup to
                     which skb belongs.

                     This helper can be used on TC egress path, but not on ingress.

                     The net_cls cgroup provides an interface to tag network packets based  on  a
                     user-provided  identifier for all traffic coming from the tasks belonging to
                     the related cgroup. See also the  related  kernel  documentation,  available
                     from           the          Linux          sources          in          file
                     Documentation/admin-guide/cgroup-v1/net_cls.rst.

                     The Linux kernel has two versions for cgroups:  there  are  cgroups  v1  and
                     cgroups  v2. Both are available to users, who can use a mixture of them, but
                     note that  the  net_cls  cgroup  is  for  cgroup  v1  only.  This  makes  it
                     incompatible  with  BPF  programs  run on cgroups, which is a cgroup-v2-only
                     feature (a socket can only hold data for one version of cgroups at a time).

                     This  helper  is  only  available  is  the  kernel  was  compiled  with  the
                     CONFIG_CGROUP_NET_CLASSID configuration option set to "y" or to "m".

              Return The classid, or 0 for the default unconfigured classid.

       long bpf_skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci)

              Description
                     Push a vlan_tci (VLAN tag control information) of protocol vlan_proto to the
                     packet associated to skb, then update the checksum. Note that if  vlan_proto
                     is  different  from  ETH_P_8021Q  and  ETH_P_8021AD,  it is considered to be
                     ETH_P_8021Q.

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore,  at  load  time,  all  checks  on pointers previously done by the
                     verifier are invalidated and must be performed again, if the helper is  used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       long bpf_skb_vlan_pop(struct sk_buff *skb)

              Description
                     Pop a VLAN header from the packet associated to skb.

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore, at load time, all checks  on  pointers  previously  done  by  the
                     verifier  are invalidated and must be performed again, if the helper is used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       long bpf_skb_get_tunnel_key(struct sk_buff *skb, struct bpf_tunnel_key *key, u32 size, u64
       flags)

              Description
                     Get  tunnel  metadata.  This  helper  takes a pointer key to an empty struct
                     bpf_tunnel_key of size, that will be filled with  tunnel  metadata  for  the
                     packet associated to skb.  The flags can be set to BPF_F_TUNINFO_IPV6, which
                     indicates that the tunnel is based on IPv6 protocol instead of IPv4.

                     The struct bpf_tunnel_key  is  an  object  that  generalizes  the  principal
                     parameters  used  by  various tunneling protocols into a single struct. This
                     way, it can be used to easily make a decision based on the contents  of  the
                     encapsulation  header,  "summarized" in this struct. In particular, it holds
                     the IP address of the remote end (IPv4 or IPv6, depending on  the  case)  in
                     key->remote_ipv4   or   key->remote_ipv6.  Also,  this  struct  exposes  the
                     key->tunnel_id,  which  is  generally  mapped  to  a  VNI  (Virtual  Network
                     Identifier),     making     it     programmable     together     with    the
                     bpf_skb_set_tunnel_key() helper.

                     Let's imagine that the following code is part of a program attached  to  the
                     TC  ingress interface, on one end of a GRE tunnel, and is supposed to filter
                     out all messages coming from  remote  ends  with  IPv4  address  other  than
                     10.0.0.1:

                        int ret;
                        struct bpf_tunnel_key key = {};

                        ret = bpf_skb_get_tunnel_key(skb, &key, sizeof(key), 0);
                        if (ret < 0)
                                return TC_ACT_SHOT;     // drop packet

                        if (key.remote_ipv4 != 0x0a000001)
                                return TC_ACT_SHOT;     // drop packet

                        return TC_ACT_OK;               // accept packet

                     This  interface  can  also  be  used with all encapsulation devices that can
                     operate in "collect metadata" mode: instead of having one network device per
                     specific  configuration,  the "collect metadata" mode only requires a single
                     device where the configuration can be extracted from this helper.

                     This can be used together with various tunnels such as VXLan, Geneve, GRE or
                     IP in IP (IPIP).

              Return 0 on success, or a negative error in case of failure.

       long bpf_skb_set_tunnel_key(struct sk_buff *skb, struct bpf_tunnel_key *key, u32 size, u64
       flags)

              Description
                     Populate tunnel metadata for packet associated to skb. The  tunnel  metadata
                     is  set  to  the  contents  of  key,  of  size.  The  flags  can be set to a
                     combination of the following values:

                     BPF_F_TUNINFO_IPV6
                            Indicate that the tunnel is based on IPv6 protocol instead of IPv4.

                     BPF_F_ZERO_CSUM_TX
                            For IPv4 packets, add a  flag  to  tunnel  metadata  indicating  that
                            checksum computation should be skipped and checksum set to zeroes.

                     BPF_F_DONT_FRAGMENT
                            Add  a  flag to tunnel metadata indicating that the packet should not
                            be fragmented.

                     BPF_F_SEQ_NUMBER
                            Add a flag to tunnel  metadata  indicating  that  a  sequence  number
                            should be added to tunnel header before sending the packet. This flag
                            was added for  GRE  encapsulation,  but  might  be  used  with  other
                            protocols as well in the future.

                     Here is a typical usage on the transmit path:

                        struct bpf_tunnel_key key;
                             populate key ...
                        bpf_skb_set_tunnel_key(skb, &key, sizeof(key), 0);
                        bpf_clone_redirect(skb, vxlan_dev_ifindex, 0);

                     See   also  the  description  of  the  bpf_skb_get_tunnel_key()  helper  for
                     additional information.

              Return 0 on success, or a negative error in case of failure.

       u64 bpf_perf_event_read(struct bpf_map *map, u64 flags)

              Description
                     Read the value of a perf event counter. This helper relies on a map of  type
                     BPF_MAP_TYPE_PERF_EVENT_ARRAY.  The  nature  of  the  perf  event counter is
                     selected when map is updated with perf event file descriptors. The map is an
                     array  whose  size is the number of available CPUs, and each cell contains a
                     value relative to one CPU. The value to retrieve is indicated by flags, that
                     contains  the  index  of  the  CPU to look up, masked with BPF_F_INDEX_MASK.
                     Alternatively, flags can be set to BPF_F_CURRENT_CPU to  indicate  that  the
                     value for the current CPU should be retrieved.

                     Note that before Linux 4.13, only hardware perf event can be retrieved.

                     Also,   be  aware  that  the  newer  helper  bpf_perf_event_read_value()  is
                     recommended over bpf_perf_event_read() in general. The latter has  some  ABI
                     quirks  where  error  and  counter value are used as a return code (which is
                     wrong  to  do  since  ranges  may  overlap).  This  issue  is   fixed   with
                     bpf_perf_event_read_value(),  which  at the same time provides more features
                     over the bpf_perf_event_read() interface. Please refer to the description of
                     bpf_perf_event_read_value() for details.

              Return The  value  of the perf event counter read from the map, or a negative error
                     code in case of failure.

       long bpf_redirect(u32 ifindex, u64 flags)

              Description
                     Redirect the packet to another net device of index ifindex.  This helper  is
                     somewhat  similar  to  bpf_clone_redirect(),  except  that the packet is not
                     cloned, which provides increased performance.

                     Except for  XDP,  both  ingress  and  egress  interfaces  can  be  used  for
                     redirection.   The  BPF_F_INGRESS  value  in  flags  is  used  to  make  the
                     distinction (ingress path is selected if the flag is  present,  egress  path
                     otherwise).   Currently,   XDP  only  supports  redirection  to  the  egress
                     interface, and accepts no flag at all.

                     The  same  effect   can   also   be   attained   with   the   more   generic
                     bpf_redirect_map(),  which  uses  a  BPF  map  to  store the redirect target
                     instead of providing it directly to the helper.

              Return For XDP, the helper returns XDP_REDIRECT on success or XDP_ABORTED on error.
                     For  other  program  types,  the  values  are  TC_ACT_REDIRECT on success or
                     TC_ACT_SHOT on error.

       u32 bpf_get_route_realm(struct sk_buff *skb)

              Description
                     Retrieve the realm or the route, that is to say the tclassid  field  of  the
                     destination  for  the  skb. The identifier retrieved is a user-provided tag,
                     similar to the one  used  with  the  net_cls  cgroup  (see  description  for
                     bpf_get_cgroup_classid()  helper),  but  here this tag is held by a route (a
                     destination entry), not by a task.

                     Retrieving this identifier works with the clsact TC egress  hook  (see  also
                     tc-bpf(8)), or alternatively on conventional classful egress qdiscs, but not
                     on TC ingress path. In case of clsact TC egress hook, this has the advantage
                     that,  internally,  the  destination  entry  has not been dropped yet in the
                     transmit path.  Therefore,  the  destination  entry  does  not  need  to  be
                     artificially held via netif_keep_dst() for a classful qdisc until the skb is
                     freed.

                     This  helper  is  available  only  if   the   kernel   was   compiled   with
                     CONFIG_IP_ROUTE_CLASSID configuration option.

              Return The  realm  of  the route for the packet associated to skb, or 0 if none was
                     found.

       long bpf_perf_event_output(void *ctx, struct bpf_map *map,  u64  flags,  void  *data,  u64
       size)

              Description
                     Write  raw  data  blob  into  a  special  BPF perf event held by map of type
                     BPF_MAP_TYPE_PERF_EVENT_ARRAY. This  perf  event  must  have  the  following
                     attributes:  PERF_SAMPLE_RAW as sample_type, PERF_TYPE_SOFTWARE as type, and
                     PERF_COUNT_SW_BPF_OUTPUT as config.

                     The flags are used to indicate the index in map for which the value must  be
                     put,  masked  with  BPF_F_INDEX_MASK.   Alternatively,  flags  can be set to
                     BPF_F_CURRENT_CPU to indicate that the index of the current CPU core  should
                     be used.

                     The  value  to  write,  of size, is passed through eBPF stack and pointed by
                     data.

                     The context of the program ctx needs also be passed to the helper.

                     On user  space,  a  program  willing  to  read  the  values  needs  to  call
                     perf_event_open()  on the perf event (either for one or for all CPUs) and to
                     store the file descriptor into the map. This must be done  before  the  eBPF
                     program   can   send   data  into  it.  An  example  is  available  in  file
                     samples/bpf/trace_output_user.c in the Linux kernel source  tree  (the  eBPF
                     program counterpart is in samples/bpf/trace_output_kern.c).

                     bpf_perf_event_output()  achieves better performance than bpf_trace_printk()
                     for sharing data with user space, and is much better suitable for  streaming
                     data from eBPF programs.

                     Note that this helper is not restricted to tracing use cases and can be used
                     with programs attached to TC or XDP as well, where  it  allows  for  passing
                     data to user space listeners. Data can be:

                     · Only custom structs,

                     · Only the packet payload, or

                     · A combination of both.

              Return 0 on success, or a negative error in case of failure.

       long bpf_skb_load_bytes(const void *skb, u32 offset, void *to, u32 len)

              Description
                     This  helper  was provided as an easy way to load data from a packet. It can
                     be used to load len bytes from offset from the  packet  associated  to  skb,
                     into the buffer pointed by to.

                     Since  Linux  4.7,  usage of this helper has mostly been replaced by "direct
                     packet access", enabling packet data to be manipulated  with  skb->data  and
                     skb->data_end  pointing respectively to the first byte of packet data and to
                     the byte after the last byte of packet data. However, it remains  useful  if
                     one  wishes  to read large quantities of data at once from a packet into the
                     eBPF stack.

              Return 0 on success, or a negative error in case of failure.

       long bpf_get_stackid(void *ctx, struct bpf_map *map, u64 flags)

              Description
                     Walk a user or a kernel stack and return its id. To achieve this, the helper
                     needs ctx, which is a pointer to the context on which the tracing program is
                     executed, and a pointer to a map of type BPF_MAP_TYPE_STACK_TRACE.

                     The last argument, flags, holds the number of stack frames to skip  (from  0
                     to 255), masked with BPF_F_SKIP_FIELD_MASK. The next bits can be used to set
                     a combination of the following flags:

                     BPF_F_USER_STACK
                            Collect a user space stack instead of a kernel stack.

                     BPF_F_FAST_STACK_CMP
                            Compare stacks by hash only.

                     BPF_F_REUSE_STACKID
                            If two different stacks hash into the same stackid, discard  the  old
                            one.

                     The  stack id retrieved is a 32 bit long integer handle which can be further
                     combined with other data (including other stack ids) and used as a key  into
                     maps.  This  can be useful for generating a variety of graphs (such as flame
                     graphs or off-cpu graphs).

                     For walking a stack, this helper is an  improvement  over  bpf_probe_read(),
                     which  can  be  used with unrolled loops but is not efficient and consumes a
                     lot of eBPF instructions.  Instead,  bpf_get_stackid()  can  collect  up  to
                     PERF_MAX_STACK_DEPTH  both  kernel and user frames. Note that this limit can
                     be controlled with the sysctl  program,  and  that  it  should  be  manually
                     increased  in  order  to  profile  long user stacks (such as stacks for Java
                     programs). To do so, use:

                        # sysctl kernel.perf_event_max_stack=<new value>

              Return The positive or null stack id on success, or a negative  error  in  case  of
                     failure.

       s64 bpf_csum_diff(__be32 *from, u32 from_size, __be32 *to, u32 to_size, __wsum seed)

              Description
                     Compute  a  checksum  difference,  from  the  raw buffer pointed by from, of
                     length from_size (that must be a multiple of  4),  towards  the  raw  buffer
                     pointed  by to, of size to_size (same remark). An optional seed can be added
                     to the value (this can be cascaded, the seed may come from a  previous  call
                     to the helper).

                     This is flexible enough to be used in several ways:

                     · With  from_size == 0, to_size > 0 and seed set to checksum, it can be used
                       when pushing new data.

                     · With from_size > 0, to_size == 0 and seed set to checksum, it can be  used
                       when removing data from a packet.

                     · With  from_size  >  0,  to_size  >  0 and seed set to 0, it can be used to
                       compute a diff. Note that from_size and to_size do not need to be equal.

                     This helper can  be  used  in  combination  with  bpf_l3_csum_replace()  and
                     bpf_l4_csum_replace(), to which one can feed in the difference computed with
                     bpf_csum_diff().

              Return The checksum result, or a negative error code in case of failure.

       long bpf_skb_get_tunnel_opt(struct sk_buff *skb, void *opt, u32 size)

              Description
                     Retrieve tunnel options metadata for the packet associated to skb, and store
                     the raw tunnel option data to the buffer opt of size.

                     This  helper  can  be  used  with  encapsulation devices that can operate in
                     "collect metadata" mode (please refer to the related note in the description
                     of  bpf_skb_get_tunnel_key()  for  more details). A particular example where
                     this can be used is in combination with the Geneve  encapsulation  protocol,
                     where  it  allows  for  pushing  (with  bpf_skb_get_tunnel_opt() helper) and
                     retrieving arbitrary TLVs (Type-Length-Value headers) from the eBPF program.
                     This allows for full customization of these headers.

              Return The size of the option data retrieved.

       long bpf_skb_set_tunnel_opt(struct sk_buff *skb, void *opt, u32 size)

              Description
                     Set  tunnel  options metadata for the packet associated to skb to the option
                     data contained in the raw buffer opt of size.

                     See  also  the  description  of  the  bpf_skb_get_tunnel_opt()  helper   for
                     additional information.

              Return 0 on success, or a negative error in case of failure.

       long bpf_skb_change_proto(struct sk_buff *skb, __be16 proto, u64 flags)

              Description
                     Change  the protocol of the skb to proto. Currently supported are transition
                     from IPv4 to IPv6, and from IPv6 to IPv4.  The  helper  takes  care  of  the
                     groundwork  for  the  transition,  including resizing the socket buffer. The
                     eBPF  program  is  expected  to  fill  the  new   headers,   if   any,   via
                     skb_store_bytes()  and to recompute the checksums with bpf_l3_csum_replace()
                     and bpf_l4_csum_replace(). The main case for this helper is to perform NAT64
                     operations out of an eBPF program.

                     Internally,  the GSO type is marked as dodgy so that headers are checked and
                     segments are recalculated by the GSO/GRO engine.  The size for GSO target is
                     adapted as well.

                     All  values  for  flags  are  reserved for future usage, and must be left at
                     zero.

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore,  at  load  time,  all  checks  on pointers previously done by the
                     verifier are invalidated and must be performed again, if the helper is  used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       long bpf_skb_change_type(struct sk_buff *skb, u32 type)

              Description
                     Change  the packet type for the packet associated to skb. This comes down to
                     setting skb->pkt_type to type, except the eBPF program does not have a write
                     access  to  skb->pkt_type beside this helper. Using a helper here allows for
                     graceful handling of errors.

                     The major use case is to  change  incoming  skb*s  to  **PACKET_HOST*  in  a
                     programmatic   way  instead  of  having  to  recirculate  via  redirect(...,
                     BPF_F_INGRESS), for example.

                     Note that type only allows certain values. At this time, they are:

                     PACKET_HOST
                            Packet is for us.

                     PACKET_BROADCAST
                            Send packet to all.

                     PACKET_MULTICAST
                            Send packet to group.

                     PACKET_OTHERHOST
                            Send packet to someone else.

              Return 0 on success, or a negative error in case of failure.

       long bpf_skb_under_cgroup(struct sk_buff *skb, struct bpf_map *map, u32 index)

              Description
                     Check whether skb is a descendant  of  the  cgroup2  held  by  map  of  type
                     BPF_MAP_TYPE_CGROUP_ARRAY, at index.

              Return The return value depends on the result of the test, and can be:

                     · 0, if the skb failed the cgroup2 descendant test.

                     · 1, if the skb succeeded the cgroup2 descendant test.

                     · A negative error code, if an error occurred.

       u32 bpf_get_hash_recalc(struct sk_buff *skb)

              Description
                     Retrieve  the hash of the packet, skb->hash. If it is not set, in particular
                     if the hash was cleared due to mangling, recompute this hash. Later accesses
                     to the hash can be done directly with skb->hash.

                     Calling   bpf_set_hash_invalid(),   changing   a   packet   prototype   with
                     bpf_skb_change_proto(),   or   calling   bpf_skb_store_bytes()   with    the
                     BPF_F_INVALIDATE_HASH  are  actions  susceptible  to  clear  the hash and to
                     trigger a new computation for the next call to bpf_get_hash_recalc().

              Return The 32-bit hash.

       u64 bpf_get_current_task(void)

              Return A pointer to the current task struct.

       long bpf_probe_write_user(void *dst, const void *src, u32 len)

              Description
                     Attempt in a safe way to write len bytes from  the  buffer  src  to  dst  in
                     memory.  It only works for threads that are in user context, and dst must be
                     a valid user space address.

                     This helper should not be used to implement any kind of  security  mechanism
                     because  of  TOC-TOU  attacks,  but  rather to debug, divert, and manipulate
                     execution of semi-cooperative processes.

                     Keep in mind that this feature is meant for experiments, and it has  a  risk
                     of  crashing  the  system  and  running  programs.   Therefore, when an eBPF
                     program using this helper is attached, a warning including PID  and  process
                     name is printed to kernel logs.

              Return 0 on success, or a negative error in case of failure.

       long bpf_current_task_under_cgroup(struct bpf_map *map, u32 index)

              Description
                     Check whether the probe is being run is the context of a given subset of the
                     cgroup2  hierarchy.  The  cgroup2  to  test  is  held   by   map   of   type
                     BPF_MAP_TYPE_CGROUP_ARRAY, at index.

              Return The return value depends on the result of the test, and can be:

                     · 0, if the skb task belongs to the cgroup2.

                     · 1, if the skb task does not belong to the cgroup2.

                     · A negative error code, if an error occurred.

       long bpf_skb_change_tail(struct sk_buff *skb, u32 len, u64 flags)

              Description
                     Resize (trim or grow) the packet associated to skb to the new len. The flags
                     are reserved for future usage, and must be left at zero.

                     The basic idea is that the helper performs the needed  work  to  change  the
                     size of the packet, then the eBPF program rewrites the rest via helpers like
                     bpf_skb_store_bytes(),  bpf_l3_csum_replace(),   bpf_l3_csum_replace()   and
                     others. This helper is a slow path utility intended for replies with control
                     messages. And because it is targeted for slow path, the  helper  itself  can
                     afford  to  be  slow:  it implicitly linearizes, unclones and drops offloads
                     from the skb.

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore,  at  load  time,  all  checks  on pointers previously done by the
                     verifier are invalidated and must be performed again, if the helper is  used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       long bpf_skb_pull_data(struct sk_buff *skb, u32 len)

              Description
                     Pull in non-linear data in case the skb is non-linear and not all of len are
                     part of the linear section. Make len bytes from skb readable  and  writable.
                     If  a  zero  value  is  passed  for len, then the whole length of the skb is
                     pulled.

                     This helper is only needed  for  reading  and  writing  with  direct  packet
                     access.

                     For  direct  packet access, testing that offsets to access are within packet
                     boundaries (test on skb->data_end) is susceptible to  fail  if  offsets  are
                     invalid,  or  if  the  requested  data is in non-linear parts of the skb. On
                     failure the program can just bail out,  or  in  the  case  of  a  non-linear
                     buffer,  use  a  helper to make the data available. The bpf_skb_load_bytes()
                     helper is a first solution to access the data. Another one consists in using
                     bpf_skb_pull_data  to  pull in once the non-linear parts, then retesting and
                     eventually access the data.

                     At the same time, this also makes sure the  skb  is  uncloned,  which  is  a
                     necessary  condition  for direct write. As this needs to be an invariant for
                     the write part only, the verifier detects writes and adds a prologue that is
                     calling  bpf_skb_pull_data()  to  effectively  unclone the skb from the very
                     beginning in case it is indeed cloned.

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore,  at  load  time,  all  checks  on pointers previously done by the
                     verifier are invalidated and must be performed again, if the helper is  used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       s64 bpf_csum_update(struct sk_buff *skb, __wsum csum)

              Description
                     Add  the  checksum  csum  into  skb->csum  in case the driver has supplied a
                     checksum for the entire packet into that field. Return an  error  otherwise.
                     This  helper  is intended to be used in combination with bpf_csum_diff(), in
                     particular when the checksum needs to be updated after data has been written
                     into the packet through direct packet access.

              Return The checksum on success, or a negative error code in case of failure.

       void bpf_set_hash_invalid(struct sk_buff *skb)

              Description
                     Invalidate  the  current skb->hash. It can be used after mangling on headers
                     through direct packet access, in order to indicate that the hash is outdated
                     and to trigger a recalculation the next time the kernel tries to access this
                     hash or when the bpf_get_hash_recalc() helper is called.

       long bpf_get_numa_node_id(void)

              Description
                     Return the id of the current NUMA node. The primary use case for this helper
                     is  the  selection  of  sockets for the local NUMA node, when the program is
                     attached to sockets using  the  SO_ATTACH_REUSEPORT_EBPF  option  (see  also
                     socket(7)),  but  the  helper is also available to other eBPF program types,
                     similarly to bpf_get_smp_processor_id().

              Return The id of current NUMA node.

       long bpf_skb_change_head(struct sk_buff *skb, u32 len, u64 flags)

              Description
                     Grows headroom of packet associated to skb and adjusts the offset of the MAC
                     header  accordingly, adding len bytes of space. It automatically extends and
                     reallocates memory as required.

                     This helper can be used  on  a  layer  3  skb  to  push  a  MAC  header  for
                     redirection into a layer 2 device.

                     All  values  for  flags  are  reserved for future usage, and must be left at
                     zero.

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore,  at  load  time,  all  checks  on pointers previously done by the
                     verifier are invalidated and must be performed again, if the helper is  used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       long bpf_xdp_adjust_head(struct xdp_buff *xdp_md, int delta)

              Description
                     Adjust (move) xdp_md->data by delta bytes. Note that it is possible to use a
                     negative value for delta. This helper can be used to prepare the packet  for
                     pushing or popping headers.

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore, at load time, all checks  on  pointers  previously  done  by  the
                     verifier  are invalidated and must be performed again, if the helper is used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       long bpf_probe_read_str(void *dst, u32 size, const void *unsafe_ptr)

              Description
                     Copy a NUL terminated string from an unsafe  kernel  address  unsafe_ptr  to
                     dst. See bpf_probe_read_kernel_str() for more details.

                     Generally,   use  bpf_probe_read_user_str()  or  bpf_probe_read_kernel_str()
                     instead.

              Return On success, the strictly  positive  length  of  the  string,  including  the
                     trailing NUL character. On error, a negative value.

       u64 bpf_get_socket_cookie(struct sk_buff *skb)

              Description
                     If the struct sk_buff pointed by skb has a known socket, retrieve the cookie
                     (generated by the kernel) of this socket.  If no cookie has  been  set  yet,
                     generate  a new cookie. Once generated, the socket cookie remains stable for
                     the life of the socket. This helper can be useful for monitoring per  socket
                     networking traffic statistics as it provides a global socket identifier that
                     can be assumed unique.

              Return A 8-byte long non-decreasing number on success, or 0 if the socket field  is
                     missing inside skb.

       u64 bpf_get_socket_cookie(struct bpf_sock_addr *ctx)

              Description
                     Equivalent  to  bpf_get_socket_cookie()  helper  that  accepts skb, but gets
                     socket from struct bpf_sock_addr context.

              Return A 8-byte long non-decreasing number.

       u64 bpf_get_socket_cookie(struct bpf_sock_ops *ctx)

              Description
                     Equivalent to bpf_get_socket_cookie() helper  that  accepts  skb,  but  gets
                     socket from struct bpf_sock_ops context.

              Return A 8-byte long non-decreasing number.

       u32 bpf_get_socket_uid(struct sk_buff *skb)

              Return The  owner UID of the socket associated to skb. If the socket is NULL, or if
                     it is not a full socket (i.e. if it is  a  time-wait  or  a  request  socket
                     instead), overflowuid value is returned (note that overflowuid might also be
                     the actual UID value for the socket).

       long bpf_set_hash(struct sk_buff *skb, u32 hash)

              Description
                     Set the full hash for skb (set the field skb->hash) to value hash.

              Return 0

       long bpf_setsockopt(void *bpf_socket, int level, int optname, void *optval, int optlen)

              Description
                     Emulate a call to setsockopt() on the socket associated to bpf_socket, which
                     must  be  a  full socket. The level at which the option resides and the name
                     optname of  the  option  must  be  specified,  see  setsockopt(2)  for  more
                     information.  The option value of length optlen is pointed by optval.

                     bpf_socket should be one of the following:

                     · struct bpf_sock_ops for BPF_PROG_TYPE_SOCK_OPS.

                     · struct       bpf_sock_addr      for      BPF_CGROUP_INET4_CONNECT      and
                       BPF_CGROUP_INET6_CONNECT.

                     This helper actually implements a subset of setsockopt().  It  supports  the
                     following levels:

                     · SOL_SOCKET,  which  supports the following optnames: SO_RCVBUF, SO_SNDBUF,
                       SO_MAX_PACING_RATE, SO_PRIORITY,  SO_RCVLOWAT,  SO_MARK,  SO_BINDTODEVICE,
                       SO_KEEPALIVE.

                     · IPPROTO_TCP,   which  supports  the  following  optnames:  TCP_CONGESTION,
                       TCP_BPF_IW,     TCP_BPF_SNDCWND_CLAMP,     TCP_SAVE_SYN,     TCP_KEEPIDLE,
                       TCP_KEEPINTVL, TCP_KEEPCNT, TCP_SYNCNT, TCP_USER_TIMEOUT.

                     · IPPROTO_IP, which supports optname IP_TOS.

                     · IPPROTO_IPV6, which supports optname IPV6_TCLASS.

              Return 0 on success, or a negative error in case of failure.

       long bpf_skb_adjust_room(struct sk_buff *skb, s32 len_diff, u32 mode, u64 flags)

              Description
                     Grow  or  shrink  the  room  for  data  in  the  packet associated to skb by
                     len_diff, and according to the selected mode.

                     By default, the helper will reset any offloaded checksum  indicator  of  the
                     skb to CHECKSUM_NONE. This can be avoided by the following flag:

                     · BPF_F_ADJ_ROOM_NO_CSUM_RESET:  Do not reset offloaded checksum data of the
                       skb to CHECKSUM_NONE.

                     There are two supported modes at this time:

                     · BPF_ADJ_ROOM_MAC: Adjust room at the mac layer (room  space  is  added  or
                       removed below the layer 2 header).

                     · BPF_ADJ_ROOM_NET: Adjust room at the network layer (room space is added or
                       removed below the layer 3 header).

                     The following flags are supported at this time:

                     · BPF_F_ADJ_ROOM_FIXED_GSO: Do not adjust gso_size.  Adjusting mss  in  this
                       way is not allowed for datagrams.

                     · BPF_F_ADJ_ROOM_ENCAP_L3_IPV4,  BPF_F_ADJ_ROOM_ENCAP_L3_IPV6: Any new space
                       is reserved to hold a tunnel header.   Configure  skb  offsets  and  other
                       fields accordingly.

                     · BPF_F_ADJ_ROOM_ENCAP_L4_GRE,    BPF_F_ADJ_ROOM_ENCAP_L4_UDP:    Use   with
                       ENCAP_L3 flags to further specify the tunnel type.

                     · BPF_F_ADJ_ROOM_ENCAP_L2(len):  Use  with  ENCAP_L3/L4  flags  to   further
                       specify the tunnel type; len is the length of the inner MAC header.

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore, at load time, all checks  on  pointers  previously  done  by  the
                     verifier  are invalidated and must be performed again, if the helper is used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       long bpf_redirect_map(struct bpf_map *map, u32 key, u64 flags)

              Description
                     Redirect the packet  to  the  endpoint  referenced  by  map  at  index  key.
                     Depending  on  its type, this map can contain references to net devices (for
                     forwarding packets through other ports), or to  CPUs  (for  redirecting  XDP
                     frames  to  another  CPU;  but this is only implemented for native XDP (with
                     driver support) as of this writing).

                     The lower two bits of flags are used as the return code if  the  map  lookup
                     fails. This is so that the return value can be one of the XDP program return
                     codes up to XDP_TX, as chosen by the caller. Any higher bits  in  the  flags
                     argument must be unset.

                     See  also bpf_redirect(), which only supports redirecting to an ifindex, but
                     doesn't require a map to do so.

              Return XDP_REDIRECT on success, or the value of the two lower  bits  of  the  flags
                     argument on error.

       long bpf_sk_redirect_map(struct sk_buff *skb, struct bpf_map *map, u32 key, u64 flags)

              Description
                     Redirect   the   packet   to   the   socket   referenced  by  map  (of  type
                     BPF_MAP_TYPE_SOCKMAP) at index key. Both ingress and egress  interfaces  can
                     be  used  for  redirection. The BPF_F_INGRESS value in flags is used to make
                     the distinction (ingress path is selected if the  flag  is  present,  egress
                     path otherwise). This is the only flag supported for now.

              Return SK_PASS on success, or SK_DROP on error.

       long  bpf_sock_map_update(struct  bpf_sock_ops *skops, struct bpf_map *map, void *key, u64
       flags)

              Description
                     Add an entry to, or update a map referencing sockets. The skops is used as a
                     new value for the entry associated to key. flags is one of:

                     BPF_NOEXIST
                            The entry for key must not exist in the map.

                     BPF_EXIST
                            The entry for key must already exist in the map.

                     BPF_ANY
                            No condition on the existence of the entry for key.

                     If  the  map has eBPF programs (parser and verdict), those will be inherited
                     by the socket being added.  If  the  socket  is  already  attached  to  eBPF
                     programs, this results in an error.

              Return 0 on success, or a negative error in case of failure.

       long bpf_xdp_adjust_meta(struct xdp_buff *xdp_md, int delta)

              Description
                     Adjust  the  address  pointed  by  xdp_md->data_meta  by delta (which can be
                     positive or negative). Note that this operation modifies the address  stored
                     in xdp_md->data, so the latter must be loaded only after the helper has been
                     called.

                     The use of xdp_md->data_meta is optional and programs are  not  required  to
                     use it. The rationale is that when the packet is processed with XDP (e.g. as
                     DoS filter), it is possible to push further meta data along with  it  before
                     passing to the stack, and to give the guarantee that an ingress eBPF program
                     attached as a TC classifier on the same device can pick this up for  further
                     post-processing.  Since TC works with socket buffers, it remains possible to
                     set from XDP the mark or priority pointers, or other pointers for the socket
                     buffer.   Having this scratch space generic and programmable allows for more
                     flexibility as the user is free to store whatever meta data they need.

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore,  at  load  time,  all  checks  on pointers previously done by the
                     verifier are invalidated and must be performed again, if the helper is  used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       long bpf_perf_event_read_value(struct bpf_map *map, u64 flags, struct bpf_perf_event_value
       *buf, u32 buf_size)

              Description
                     Read the value of a perf event counter,  and  store  it  into  buf  of  size
                     buf_size. This helper relies on a map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY.
                     The nature of the perf event counter is selected when map  is  updated  with
                     perf event file descriptors. The map is an array whose size is the number of
                     available CPUs, and each cell contains a value  relative  to  one  CPU.  The
                     value  to retrieve is indicated by flags, that contains the index of the CPU
                     to look up, masked with BPF_F_INDEX_MASK. Alternatively, flags can be set to
                     BPF_F_CURRENT_CPU  to  indicate that the value for the current CPU should be
                     retrieved.

                     This helper behaves in a way close  to  bpf_perf_event_read()  helper,  save
                     that  instead  of  just  returning  the  value  observed,  it  fills the buf
                     structure. This allows for additional data to be retrieved:  in  particular,
                     the   enabled   and   running   times  (in  buf->enabled  and  buf->running,
                     respectively)  are  copied.  In  general,   bpf_perf_event_read_value()   is
                     recommended  over  bpf_perf_event_read(),  which  has  some  ABI  issues and
                     provides fewer functionalities.

                     These values are interesting, because hardware PMU  (Performance  Monitoring
                     Unit)  counters  are  limited  resources. When there are more PMU based perf
                     events opened than available counters, kernel will multiplex these events so
                     each  event  gets  certain percentage (but not all) of the PMU time. In case
                     that multiplexing happens, the number of samples or counter value  will  not
                     reflect  the  case  compared  to  when  no  multiplexing  occurs. This makes
                     comparison between different runs difficult.  Typically, the  counter  value
                     should  be  normalized  before  comparing  to  other  experiments. The usual
                     normalization is done as follows.

                        normalized_counter = counter * t_enabled / t_running

                     Where t_enabled is the time enabled for event  and  t_running  is  the  time
                     running  for  event  since last normalization. The enabled and running times
                     are accumulated since the perf event open. To achieve scaling factor between
                     two  invocations  of an eBPF program, users can use CPU id as the key (which
                     is typical for perf array usage model) to remember the previous value and do
                     the calculation inside the eBPF program.

              Return 0 on success, or a negative error in case of failure.

       long bpf_perf_prog_read_value(struct bpf_perf_event_data *ctx, struct bpf_perf_event_value
       *buf, u32 buf_size)

              Description
                     For en eBPF program attached to a perf event,  retrieve  the  value  of  the
                     event counter associated to ctx and store it in the structure pointed by buf
                     and of size buf_size. Enabled and running  times  are  also  stored  in  the
                     structure  (see  description  of helper bpf_perf_event_read_value() for more
                     details).

              Return 0 on success, or a negative error in case of failure.

       long bpf_getsockopt(void *bpf_socket, int level, int optname, void *optval, int optlen)

              Description
                     Emulate a call to getsockopt() on the socket associated to bpf_socket, which
                     must  be  a  full socket. The level at which the option resides and the name
                     optname of  the  option  must  be  specified,  see  getsockopt(2)  for  more
                     information.   The  retrieved  value  is  stored in the structure pointed by
                     opval and of length optlen.

                     bpf_socket should be one of the following:

                     · struct bpf_sock_ops for BPF_PROG_TYPE_SOCK_OPS.

                     · struct      bpf_sock_addr      for      BPF_CGROUP_INET4_CONNECT       and
                       BPF_CGROUP_INET6_CONNECT.

                     This  helper  actually implements a subset of getsockopt().  It supports the
                     following levels:

                     · IPPROTO_TCP, which supports optname TCP_CONGESTION.

                     · IPPROTO_IP, which supports optname IP_TOS.

                     · IPPROTO_IPV6, which supports optname IPV6_TCLASS.

              Return 0 on success, or a negative error in case of failure.

       long bpf_override_return(struct pt_regs *regs, u64 rc)

              Description
                     Used for error injection, this helper uses kprobes to  override  the  return
                     value  of  the  probed function, and to set it to rc.  The first argument is
                     the context regs on which the kprobe works.

                     This helper works by  setting  the  PC  (program  counter)  to  an  override
                     function  which  is run in place of the original probed function. This means
                     the probed function is not run at all. The replacement function just returns
                     with the required value.

                     This  helper has security implications, and thus is subject to restrictions.
                     It   is   only   available   if   the   kernel   was   compiled   with   the
                     CONFIG_BPF_KPROBE_OVERRIDE  configuration  option,  and in this case it only
                     works on functions tagged with ALLOW_ERROR_INJECTION in the kernel code.

                     Also, the  helper  is  only  available  for  the  architectures  having  the
                     CONFIG_FUNCTION_ERROR_INJECTION option. As of this writing, x86 architecture
                     is the only one to support this feature.

              Return 0

       long bpf_sock_ops_cb_flags_set(struct bpf_sock_ops *bpf_sock, int argval)

              Description
                     Attempt to set the value of the bpf_sock_ops_cb_flags field for the full TCP
                     socket associated to bpf_sock_ops to argval.

                     The  primary  use  of this field is to determine if there should be calls to
                     eBPF programs of type BPF_PROG_TYPE_SOCK_OPS at various points  in  the  TCP
                     code. A program of the same type can change its value, per connection and as
                     necessary, when the  connection  is  established.  This  field  is  directly
                     accessible for reading, but this helper must be used for updates in order to
                     return an error if an eBPF program tries to  set  a  callback  that  is  not
                     supported in the current kernel.

                     argval is a flag array which can combine these flags:

                     · BPF_SOCK_OPS_RTO_CB_FLAG (retransmission time out)

                     · BPF_SOCK_OPS_RETRANS_CB_FLAG (retransmission)

                     · BPF_SOCK_OPS_STATE_CB_FLAG (TCP state change)

                     · BPF_SOCK_OPS_RTT_CB_FLAG (every RTT)

                     Therefore, this function can be used to clear a callback flag by setting the
                     appropriate bit to zero. e.g. to disable the RTO callback:

                     bpf_sock_ops_cb_flags_set(bpf_sock,
                            bpf_sock->bpf_sock_ops_cb_flags & ~BPF_SOCK_OPS_RTO_CB_FLAG)

                     Here are some examples of where one could call such eBPF program:

                     · When RTO fires.

                     · When a packet is retransmitted.

                     · When the connection terminates.

                     · When a packet is sent.

                     · When a packet is received.

              Return Code -EINVAL if the socket is not a full TCP socket; otherwise,  a  positive
                     number  containing  the  bits that could not be set is returned (which comes
                     down to 0 if all bits were set as required).

       long bpf_msg_redirect_map(struct sk_msg_buff *msg,  struct  bpf_map  *map,  u32  key,  u64
       flags)

              Description
                     This  helper  is used in programs implementing policies at the socket level.
                     If the message msg is allowed to pass (i.e.  if  the  verdict  eBPF  program
                     returns  SK_PASS),  redirect  it  to  the  socket referenced by map (of type
                     BPF_MAP_TYPE_SOCKMAP) at index key. Both ingress and egress  interfaces  can
                     be  used  for  redirection. The BPF_F_INGRESS value in flags is used to make
                     the distinction (ingress path is selected if the  flag  is  present,  egress
                     path otherwise). This is the only flag supported for now.

              Return SK_PASS on success, or SK_DROP on error.

       long bpf_msg_apply_bytes(struct sk_msg_buff *msg, u32 bytes)

              Description
                     For socket policies, apply the verdict of the eBPF program to the next bytes
                     (number of bytes) of message msg.

                     For example, this helper can be used in the following cases:

                     · A single sendmsg() or sendfile() system  call  contains  multiple  logical
                       messages that the eBPF program is supposed to read and for which it should
                       apply a verdict.

                     · An eBPF program only cares to read the  first  bytes  of  a  msg.  If  the
                       message  has a large payload, then setting up and calling the eBPF program
                       repeatedly for all bytes, even though the verdict is already known,  would
                       create unnecessary overhead.

                     When  called from within an eBPF program, the helper sets a counter internal
                     to the BPF infrastructure, that is used to apply the  last  verdict  to  the
                     next bytes. If bytes is smaller than the current data being processed from a
                     sendmsg() or sendfile() system call, the first bytes will be  sent  and  the
                     eBPF  program  will be re-run with the pointer for start of data pointing to
                     byte number bytes + 1. If bytes  is  larger  than  the  current  data  being
                     processed,  then  the  eBPF verdict will be applied to multiple sendmsg() or
                     sendfile() calls until bytes are consumed.

                     Note that if a socket closes with the internal counter  holding  a  non-zero
                     value,  this  is  not a problem because data is not being buffered for bytes
                     and is sent as it is received.

              Return 0

       long bpf_msg_cork_bytes(struct sk_msg_buff *msg, u32 bytes)

              Description
                     For socket policies, prevent the execution of the verdict eBPF  program  for
                     message msg until bytes (byte number) have been accumulated.

                     This  can be used when one needs a specific number of bytes before a verdict
                     can be assigned, even if the data spans  multiple  sendmsg()  or  sendfile()
                     calls.  The  extreme  case would be a user calling sendmsg() repeatedly with
                     1-byte long message segments. Obviously, this is bad for performance, but it
                     is  still valid. If the eBPF program needs bytes bytes to validate a header,
                     this helper can be used to prevent the eBPF program to be called again until
                     bytes have been accumulated.

              Return 0

       long bpf_msg_pull_data(struct sk_msg_buff *msg, u32 start, u32 end, u64 flags)

              Description
                     For socket policies, pull in non-linear data from user space for msg and set
                     pointers msg->data and msg->data_end to start and  end  bytes  offsets  into
                     msg, respectively.

                     If  a program of type BPF_PROG_TYPE_SK_MSG is run on a msg it can only parse
                     data that the (data, data_end) pointers have already consumed. For sendmsg()
                     hooks this is likely the first scatterlist element. But for calls relying on
                     the sendpage handler (e.g. sendfile()) this will be the range (0, 0) because
                     the  data is shared with user space and by default the objective is to avoid
                     allowing user space to modify data while (or after) eBPF  verdict  is  being
                     decided.  This  helper  can be used to pull in data and to set the start and
                     end pointer to given values. Data will be copied if necessary (i.e. if  data
                     was  not  linear  and  if  start  and  end pointers do not point to the same
                     chunk).

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore,  at  load  time,  all  checks  on pointers previously done by the
                     verifier are invalidated and must be performed again, if the helper is  used
                     in combination with direct packet access.

                     All  values  for  flags  are  reserved for future usage, and must be left at
                     zero.

              Return 0 on success, or a negative error in case of failure.

       long bpf_bind(struct bpf_sock_addr *ctx, struct sockaddr *addr, int addr_len)

              Description
                     Bind the socket associated to ctx to the address pointed by addr, of  length
                     addr_len.  This  allows  for  making outgoing connection from the desired IP
                     address, which can be useful for example when all processes inside a  cgroup
                     should use one single IP address on a host that has multiple IP configured.

                     This  helper  works  for  IPv4  and  IPv6,  TCP  and UDP sockets. The domain
                     (addr->sa_family) must be AF_INET (or AF_INET6). It's advised to  pass  zero
                     port  (sin_port  or  sin6_port)  which triggers IP_BIND_ADDRESS_NO_PORT-like
                     behavior and lets the kernel efficiently pick up an unused port as  long  as
                     4-tuple is unique. Passing non-zero port might lead to degraded performance.

              Return 0 on success, or a negative error in case of failure.

       long bpf_xdp_adjust_tail(struct xdp_buff *xdp_md, int delta)

              Description
                     Adjust (move) xdp_md->data_end by delta bytes. It is possible to both shrink
                     and grow the packet tail.  Shrink done via delta being a negative integer.

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore,  at  load  time,  all  checks  on pointers previously done by the
                     verifier are invalidated and must be performed again, if the helper is  used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       long   bpf_skb_get_xfrm_state(struct   sk_buff  *skb,  u32  index,  struct  bpf_xfrm_state
       *xfrm_state, u32 size, u64 flags)

              Description
                     Retrieve the XFRM state (IP transform framework,  see  also  ip-xfrm(8))  at
                     index in XFRM "security path" for skb.

                     The  retrieved  value  is  stored  in  the  struct bpf_xfrm_state pointed by
                     xfrm_state and of length size.

                     All values for flags are reserved for future usage,  and  must  be  left  at
                     zero.

                     This  helper  is  available only if the kernel was compiled with CONFIG_XFRM
                     configuration option.

              Return 0 on success, or a negative error in case of failure.

       long bpf_get_stack(void *ctx, void *buf, u32 size, u64 flags)

              Description
                     Return a user or a kernel stack in bpf program provided buffer.  To  achieve
                     this,  the  helper needs ctx, which is a pointer to the context on which the
                     tracing program is executed.  To  store  the  stacktrace,  the  bpf  program
                     provides buf with a nonnegative size.

                     The  last  argument, flags, holds the number of stack frames to skip (from 0
                     to 255), masked with BPF_F_SKIP_FIELD_MASK. The next bits can be used to set
                     the following flags:

                     BPF_F_USER_STACK
                            Collect a user space stack instead of a kernel stack.

                     BPF_F_USER_BUILD_ID
                            Collect  buildid+offset  instead of ips for user stack, only valid if
                            BPF_F_USER_STACK is also specified.

                     bpf_get_stack() can collect up to PERF_MAX_STACK_DEPTH both kernel and  user
                     frames, subject to sufficient large buffer size. Note that this limit can be
                     controlled with the sysctl program, and that it should be manually increased
                     in  order to profile long user stacks (such as stacks for Java programs). To
                     do so, use:

                        # sysctl kernel.perf_event_max_stack=<new value>

              Return A non-negative value equal to or less than size on success,  or  a  negative
                     error in case of failure.

       long  bpf_skb_load_bytes_relative(const  void  *skb,  u32  offset,  void *to, u32 len, u32
       start_header)

              Description
                     This helper is similar to bpf_skb_load_bytes() in that it provides  an  easy
                     way  to  load  len bytes from offset from the packet associated to skb, into
                     the buffer pointed by to. The difference to bpf_skb_load_bytes() is  that  a
                     fifth argument start_header exists in order to select a base offset to start
                     from. start_header can be one of:

                     BPF_HDR_START_MAC
                            Base offset to load data from is skb's mac header.

                     BPF_HDR_START_NET
                            Base offset to load data from is skb's network header.

                     In general, "direct packet access" is the preferred method to access  packet
                     data,  however,  this helper is in particular useful in socket filters where
                     skb->data does not always point to the start of the  mac  header  and  where
                     "direct packet access" is not available.

              Return 0 on success, or a negative error in case of failure.

       long bpf_fib_lookup(void *ctx, struct bpf_fib_lookup *params, int plen, u32 flags)

              Description
                     Do  FIB  lookup  in  kernel tables using parameters in params.  If lookup is
                     successful and result shows packet is to be forwarded, the  neighbor  tables
                     are  searched  for  the  nexthop.   If  successful  (ie.,  FIB  lookup shows
                     forwarding and nexthop is resolved), the  nexthop  address  is  returned  in
                     ipv4_dst  or  ipv6_dst based on family, smac is set to mac address of egress
                     device, dmac is set to nexthop mac address, rt_metric is set to metric  from
                     route  (IPv4/IPv6  only),  and  ifindex  is  set  to the device index of the
                     nexthop from the FIB lookup.

                     plen argument is the size of the passed in struct.  flags argument can be  a
                     combination of one or more of the following values:

                     BPF_FIB_LOOKUP_DIRECT
                            Do a direct table lookup vs full lookup using FIB rules.

                     BPF_FIB_LOOKUP_OUTPUT
                            Perform lookup from an egress perspective (default is ingress).

                     ctx  is  either  struct xdp_md for XDP programs or struct sk_buff tc cls_act
                     programs.

              Return

                     · < 0 if any input argument is invalid

                     · 0 on success (packet is forwarded, nexthop neighbor exists)

                     · > 0 one of BPF_FIB_LKUP_RET_  codes  explaining  why  the  packet  is  not
                       forwarded or needs assist from full stack

       long  bpf_sock_hash_update(struct bpf_sock_ops *skops, struct bpf_map *map, void *key, u64
       flags)

              Description
                     Add an entry to, or update a sockhash map referencing sockets.  The skops is
                     used as a new value for the entry associated to key. flags is one of:

                     BPF_NOEXIST
                            The entry for key must not exist in the map.

                     BPF_EXIST
                            The entry for key must already exist in the map.

                     BPF_ANY
                            No condition on the existence of the entry for key.

                     If  the  map has eBPF programs (parser and verdict), those will be inherited
                     by the socket being added.  If  the  socket  is  already  attached  to  eBPF
                     programs, this results in an error.

              Return 0 on success, or a negative error in case of failure.

       long  bpf_msg_redirect_hash(struct  sk_msg_buff  *msg, struct bpf_map *map, void *key, u64
       flags)

              Description
                     This helper is used in programs implementing policies at the  socket  level.
                     If  the  message  msg  is  allowed to pass (i.e. if the verdict eBPF program
                     returns SK_PASS), redirect it to the  socket  referenced  by  map  (of  type
                     BPF_MAP_TYPE_SOCKHASH)  using  hash  key. Both ingress and egress interfaces
                     can be used for redirection. The BPF_F_INGRESS value in  flags  is  used  to
                     make  the  distinction  (ingress  path  is  selected if the flag is present,
                     egress path otherwise). This is the only flag supported for now.

              Return SK_PASS on success, or SK_DROP on error.

       long bpf_sk_redirect_hash(struct sk_buff *skb, struct bpf_map *map, void *key, u64 flags)

              Description
                     This helper is used in programs implementing  policies  at  the  skb  socket
                     level.  If  the  sk_buff  skb  is allowed to pass (i.e.  if the verdict eBPF
                     program returns SK_PASS), redirect it to the socket referenced  by  map  (of
                     type   BPF_MAP_TYPE_SOCKHASH)  using  hash  key.  Both  ingress  and  egress
                     interfaces can be used for redirection. The BPF_F_INGRESS value in flags  is
                     used  to  make  the  distinction  (ingress  path  is selected if the flag is
                     present, egress otherwise). This is the only flag supported for now.

              Return SK_PASS on success, or SK_DROP on error.

       long bpf_lwt_push_encap(struct sk_buff *skb, u32 type, void *hdr, u32 len)

              Description
                     Encapsulate the packet associated to skb within a Layer 3  protocol  header.
                     This  header  is provided in the buffer at address hdr, with len its size in
                     bytes. type indicates the protocol of the header and can be one of:

                     BPF_LWT_ENCAP_SEG6
                            IPv6 encapsulation with Segment Routing Header (struct  ipv6_sr_hdr).
                            hdr only contains the SRH, the IPv6 header is computed by the kernel.

                     BPF_LWT_ENCAP_SEG6_INLINE
                            Only  works  if skb contains an IPv6 packet. Insert a Segment Routing
                            Header (struct ipv6_sr_hdr) inside the IPv6 header.

                     BPF_LWT_ENCAP_IP
                            IP encapsulation (GRE/GUE/IPIP/etc). The outer header must be IPv4 or
                            IPv6,   followed   by   zero   or  more  additional  headers,  up  to
                            LWT_BPF_MAX_HEADROOM total bytes in  all  prepended  headers.  Please
                            note that if skb_is_gso(skb) is true, no more than two headers can be
                            prepended, and the inner header, if present, should be either GRE  or
                            UDP/GUE.

                     BPF_LWT_ENCAP_SEG6*   types   can   be   called  by  BPF  programs  of  type
                     BPF_PROG_TYPE_LWT_IN; BPF_LWT_ENCAP_IP type can be called by bpf programs of
                     types BPF_PROG_TYPE_LWT_IN and BPF_PROG_TYPE_LWT_XMIT.

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore, at load time, all checks  on  pointers  previously  done  by  the
                     verifier  are invalidated and must be performed again, if the helper is used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       long bpf_lwt_seg6_store_bytes(struct sk_buff *skb, u32 offset, const void *from, u32 len)

              Description
                     Store len bytes from address from into the  packet  associated  to  skb,  at
                     offset.  Only  the  flags,  tag  and  TLVs inside the outermost IPv6 Segment
                     Routing Header can be modified through this helper.

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore,  at  load  time,  all  checks  on pointers previously done by the
                     verifier are invalidated and must be performed again, if the helper is  used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       long bpf_lwt_seg6_adjust_srh(struct sk_buff *skb, u32 offset, s32 delta)

              Description
                     Adjust  the  size  allocated  to  TLVs in the outermost IPv6 Segment Routing
                     Header contained in the packet associated to  skb,  at  position  offset  by
                     delta  bytes.  Only offsets after the segments are accepted. delta can be as
                     well positive (growing) as negative (shrinking).

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore,  at  load  time,  all  checks  on pointers previously done by the
                     verifier are invalidated and must be performed again, if the helper is  used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       long bpf_lwt_seg6_action(struct sk_buff *skb, u32 action, void *param, u32 param_len)

              Description
                     Apply an IPv6 Segment Routing action of type action to the packet associated
                     to skb. Each action takes a parameter contained at  address  param,  and  of
                     length param_len bytes.  action can be one of:

                     SEG6_LOCAL_ACTION_END_X
                            End.X  action:  Endpoint  with Layer-3 cross-connect.  Type of param:
                            struct in6_addr.

                     SEG6_LOCAL_ACTION_END_T
                            End.T action: Endpoint with specific  IPv6  table  lookup.   Type  of
                            param: int.

                     SEG6_LOCAL_ACTION_END_B6
                            End.B6  action:  Endpoint  bound  to  an SRv6 policy.  Type of param:
                            struct ipv6_sr_hdr.

                     SEG6_LOCAL_ACTION_END_B6_ENCAP
                            End.B6.Encap action: Endpoint bound to an SRv6 encapsulation  policy.
                            Type of param: struct ipv6_sr_hdr.

                     A call to this helper is susceptible to change the underlying packet buffer.
                     Therefore, at load time, all checks  on  pointers  previously  done  by  the
                     verifier  are invalidated and must be performed again, if the helper is used
                     in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       long bpf_rc_repeat(void *ctx)

              Description
                     This helper is used in  programs  implementing  IR  decoding,  to  report  a
                     successfully decoded repeat key message. This delays the generation of a key
                     up event for previously generated key down event.

                     Some IR protocols like NEC have a special  IR  message  for  repeating  last
                     button, for when a button is held down.

                     The ctx should point to the lirc sample as passed into the program.

                     This  helper  is  only  available  is  the  kernel  was  compiled  with  the
                     CONFIG_BPF_LIRC_MODE2 configuration option set to "y".

              Return 0

       long bpf_rc_keydown(void *ctx, u32 protocol, u64 scancode, u32 toggle)

              Description
                     This helper is used in  programs  implementing  IR  decoding,  to  report  a
                     successfully  decoded  key  press  with  scancode, toggle value in the given
                     protocol. The scancode will be translated to a keycode using the rc  keymap,
                     and  reported  as  an input key down event. After a period a key up event is
                     generated. This period can be extended by  calling  either  bpf_rc_keydown()
                     again with the same values, or calling bpf_rc_repeat().

                     Some  protocols  include  a  toggle bit, in case the button was released and
                     pressed again between consecutive scancodes.

                     The ctx should point to the lirc sample as passed into the program.

                     The protocol is the decoded protocol number  (see  enum  rc_proto  for  some
                     predefined values).

                     This  helper  is  only  available  is  the  kernel  was  compiled  with  the
                     CONFIG_BPF_LIRC_MODE2 configuration option set to "y".

              Return 0

       u64 bpf_skb_cgroup_id(struct sk_buff *skb)

              Description
                     Return the cgroup v2 id of the socket associated  with  the  skb.   This  is
                     roughly  similar  to  the  bpf_get_cgroup_classid()  helper for cgroup v1 by
                     providing a tag resp. identifier that can be matched  on  or  used  for  map
                     lookups  e.g.  to  implement policy. The cgroup v2 id of a given path in the
                     hierarchy is exposed in user space through the f_handle API in order to  get
                     to the same 64-bit id.

                     This  helper  can  be  used  on  TC  egress path, but not on ingress, and is
                     available only if the kernel was compiled with  the  CONFIG_SOCK_CGROUP_DATA
                     configuration option.

              Return The id is returned or 0 in case the id could not be retrieved.

       u64 bpf_get_current_cgroup_id(void)

              Return A 64-bit integer containing the current cgroup id based on the cgroup within
                     which the current task is running.

       void *bpf_get_local_storage(void *map, u64 flags)

              Description
                     Get the pointer to the local storage area.  The type and  the  size  of  the
                     local storage is defined by the map argument.  The flags meaning is specific
                     for each map type, and has to be 0 for cgroup local storage.

                     Depending on the BPF program type,  a  local  storage  area  can  be  shared
                     between multiple instances of the BPF program, running simultaneously.

                     A  user  should  care about the synchronization by himself.  For example, by
                     using the BPF_STX_XADD instruction to alter the shared data.

              Return A pointer to the local storage area.

       long bpf_sk_select_reuseport(struct sk_reuseport_md  *reuse,  struct  bpf_map  *map,  void
       *key, u64 flags)

              Description
                     Select  a  SO_REUSEPORT  socket from a BPF_MAP_TYPE_REUSEPORT_ARRAY map.  It
                     checks the selected socket is matching the incoming request  in  the  socket
                     buffer.

              Return 0 on success, or a negative error in case of failure.

       u64 bpf_skb_ancestor_cgroup_id(struct sk_buff *skb, int ancestor_level)

              Description
                     Return id of cgroup v2 that is ancestor of cgroup associated with the skb at
                     the ancestor_level.  The root cgroup is at ancestor_level zero and each step
                     down  the  hierarchy  increments  the  level.  If ancestor_level == level of
                     cgroup associated with skb, then return  value  will  be  same  as  that  of
                     bpf_skb_cgroup_id().

                     The  helper  is useful to implement policies based on cgroups that are upper
                     in hierarchy than immediate cgroup associated with skb.

                     The  format  of  returned  id  and  helper  limitations  are  same   as   in
                     bpf_skb_cgroup_id().

              Return The id is returned or 0 in case the id could not be retrieved.

       struct   bpf_sock   *bpf_sk_lookup_tcp(void   *ctx,   struct  bpf_sock_tuple  *tuple,  u32
       tuple_size, u64 netns, u64 flags)

              Description
                     Look for TCP socket matching tuple, optionally in a child network  namespace
                     netns.  The  return  value  must  be  checked, and if non-NULL, released via
                     bpf_sk_release().

                     The ctx should point to the context of the  program,  such  as  the  skb  or
                     socket  (depending  on  the hook in use). This is used to determine the base
                     network namespace for the lookup.

                     tuple_size must be one of:

                     sizeof(tuple->ipv4)
                            Look for an IPv4 socket.

                     sizeof(tuple->ipv6)
                            Look for an IPv6 socket.

                     If the netns is a negative signed 32-bit integer,  then  the  socket  lookup
                     table  in  the netns associated with the ctx will be used. For the TC hooks,
                     this is the netns of the device in the skb. For socket hooks,  this  is  the
                     netns of the socket.  If netns is any other signed 32-bit value greater than
                     or equal to zero then it specifies the ID of the netns relative to the netns
                     associated  with  the  ctx. netns values beyond the range of 32-bit integers
                     are reserved for future use.

                     All values for flags are reserved for future usage,  and  must  be  left  at
                     zero.

                     This  helper  is  available  only if the kernel was compiled with CONFIG_NET
                     configuration option.

              Return Pointer to struct bpf_sock, or NULL in case of failure.   For  sockets  with
                     reuseport  option,  the  struct bpf_sock result is from reuse->socks[] using
                     the hash of the tuple.

       struct  bpf_sock  *bpf_sk_lookup_udp(void  *ctx,   struct   bpf_sock_tuple   *tuple,   u32
       tuple_size, u64 netns, u64 flags)

              Description
                     Look  for UDP socket matching tuple, optionally in a child network namespace
                     netns. The return value must be  checked,  and  if  non-NULL,  released  via
                     bpf_sk_release().

                     The  ctx  should  point  to  the  context of the program, such as the skb or
                     socket (depending on the hook in use). This is used to  determine  the  base
                     network namespace for the lookup.

                     tuple_size must be one of:

                     sizeof(tuple->ipv4)
                            Look for an IPv4 socket.

                     sizeof(tuple->ipv6)
                            Look for an IPv6 socket.

                     If  the  netns  is  a negative signed 32-bit integer, then the socket lookup
                     table in the netns associated with the ctx will be used. For the  TC  hooks,
                     this  is  the  netns of the device in the skb. For socket hooks, this is the
                     netns of the socket.  If netns is any other signed 32-bit value greater than
                     or equal to zero then it specifies the ID of the netns relative to the netns
                     associated with the ctx. netns values beyond the range  of  32-bit  integers
                     are reserved for future use.

                     All  values  for  flags  are  reserved for future usage, and must be left at
                     zero.

                     This helper is available only if the kernel  was  compiled  with  CONFIG_NET
                     configuration option.

              Return Pointer  to  struct  bpf_sock, or NULL in case of failure.  For sockets with
                     reuseport option, the struct bpf_sock result is  from  reuse->socks[]  using
                     the hash of the tuple.

       long bpf_sk_release(struct bpf_sock *sock)

              Description
                     Release the reference held by sock. sock must be a non-NULL pointer that was
                     returned from bpf_sk_lookup_xxx().

              Return 0 on success, or a negative error in case of failure.

       long bpf_map_push_elem(struct bpf_map *map, const void *value, u64 flags)

              Description
                     Push an element value in map. flags is one of:

                     BPF_EXIST
                            If the queue/stack is full, the oldest element  is  removed  to  make
                            room for this.

              Return 0 on success, or a negative error in case of failure.

       long bpf_map_pop_elem(struct bpf_map *map, void *value)

              Description
                     Pop an element from map.

              Return 0 on success, or a negative error in case of failure.

       long bpf_map_peek_elem(struct bpf_map *map, void *value)

              Description
                     Get an element from map without removing it.

              Return 0 on success, or a negative error in case of failure.

       long bpf_msg_push_data(struct sk_msg_buff *msg, u32 start, u32 len, u64 flags)

              Description
                     For socket policies, insert len bytes into msg at offset start.

                     If  a  program  of  type BPF_PROG_TYPE_SK_MSG is run on a msg it may want to
                     insert metadata or options into the msg.  This can later be read and used by
                     any of the lower layer BPF hooks.

                     This  helper  may  fail  if  under memory pressure (a malloc fails) in these
                     cases BPF programs will get an appropriate error and BPF programs will  need
                     to handle them.

              Return 0 on success, or a negative error in case of failure.

       long bpf_msg_pop_data(struct sk_msg_buff *msg, u32 start, u32 len, u64 flags)

              Description
                     Will remove len bytes from a msg starting at byte start.  This may result in
                     ENOMEM errors under  certain  situations  if  an  allocation  and  copy  are
                     required  due  to a full ring buffer.  However, the helper will try to avoid
                     doing the allocation if possible. Other errors can occur if input parameters
                     are  invalid  either  due  to start byte not being valid part of msg payload
                     and/or pop value being to large.

              Return 0 on success, or a negative error in case of failure.

       long bpf_rc_pointer_rel(void *ctx, s32 rel_x, s32 rel_y)

              Description
                     This helper is used in  programs  implementing  IR  decoding,  to  report  a
                     successfully decoded pointer movement.

                     The ctx should point to the lirc sample as passed into the program.

                     This  helper  is  only  available  is  the  kernel  was  compiled  with  the
                     CONFIG_BPF_LIRC_MODE2 configuration option set to "y".

              Return 0

       long bpf_spin_lock(struct bpf_spin_lock *lock)

              Description
                     Acquire a spinlock represented by the pointer lock, which is stored as  part
                     of a value of a map. Taking the lock allows to safely update the rest of the
                     fields in that value. The spinlock can (and must) later be released  with  a
                     call to bpf_spin_unlock(lock).

                     Spinlocks   in   BPF  programs  come  with  a  number  of  restrictions  and
                     constraints:

                     · bpf_spin_lock  objects   are   only   allowed   inside   maps   of   types
                       BPF_MAP_TYPE_HASH  and  BPF_MAP_TYPE_ARRAY (this list could be extended in
                       the future).

                     · BTF description of the map is mandatory.

                     · The BPF program can take ONE lock at a time,  since  taking  two  or  more
                       could cause dead locks.

                     · Only one struct bpf_spin_lock is allowed per map element.

                     · When  the  lock  is  taken,  calls  (either BPF to BPF or helpers) are not
                       allowed.

                     · The BPF_LD_ABS and  BPF_LD_IND  instructions  are  not  allowed  inside  a
                       spinlock-ed region.

                     · The  BPF  program  MUST call bpf_spin_unlock() to release the lock, on all
                       execution paths, before it returns.

                     · The  BPF  program  can  access   struct   bpf_spin_lock   only   via   the
                       bpf_spin_lock()  and  bpf_spin_unlock()  helpers.  Loading or storing data
                       into the struct bpf_spin_lock lock; field of a map is not allowed.

                     · To use the bpf_spin_lock() helper, the BTF description of  the  map  value
                       must  be  a struct and have struct bpf_spin_lock anyname; field at the top
                       level.  Nested lock inside another struct is not allowed.

                     · The struct bpf_spin_lock lock field in a map value must be  aligned  on  a
                       multiple of 4 bytes in that value.

                     · Syscall  with  command BPF_MAP_LOOKUP_ELEM does not copy the bpf_spin_lock
                       field to user space.

                     · Syscall with command BPF_MAP_UPDATE_ELEM, or update from a BPF program, do
                       not update the bpf_spin_lock field.

                     · bpf_spin_lock cannot be on the stack or inside a networking packet (it can
                       only be inside of a map values).

                     · bpf_spin_lock is available to root only.

                     · Tracing programs and socket filter programs cannot use bpf_spin_lock() due
                       to insufficient preemption checks (but this may change in the future).

                     · bpf_spin_lock is not allowed in inner maps of map-in-map.

              Return 0

       long bpf_spin_unlock(struct bpf_spin_lock *lock)

              Description
                     Release the lock previously locked by a call to bpf_spin_lock(lock).

              Return 0

       struct bpf_sock *bpf_sk_fullsock(struct bpf_sock *sk)

              Description
                     This  helper gets a struct bpf_sock pointer such that all the fields in this
                     bpf_sock can be accessed.

              Return A struct bpf_sock pointer on success, or NULL in case of failure.

       struct bpf_tcp_sock *bpf_tcp_sock(struct bpf_sock *sk)

              Description
                     This helper gets a  struct  bpf_tcp_sock  pointer  from  a  struct  bpf_sock
                     pointer.

              Return A struct bpf_tcp_sock pointer on success, or NULL in case of failure.

       long bpf_skb_ecn_set_ce(struct sk_buff *skb)

              Description
                     Set  ECN  (Explicit  Congestion  Notification)  field  of  IP  header  to CE
                     (Congestion Encountered) if current value is ECT  (ECN  Capable  Transport).
                     Otherwise, do nothing. Works with IPv6 and IPv4.

              Return 1 if the CE flag is set (either by the current helper call or because it was
                     already present), 0 if it is not set.

       struct bpf_sock *bpf_get_listener_sock(struct bpf_sock *sk)

              Description
                     Return a struct bpf_sock pointer in TCP_LISTEN state.   bpf_sk_release()  is
                     unnecessary and not allowed.

              Return A struct bpf_sock pointer on success, or NULL in case of failure.

       struct   bpf_sock   *bpf_skc_lookup_tcp(void   *ctx,  struct  bpf_sock_tuple  *tuple,  u32
       tuple_size, u64 netns, u64 flags)

              Description
                     Look for TCP socket matching tuple, optionally in a child network  namespace
                     netns.  The  return  value  must  be  checked, and if non-NULL, released via
                     bpf_sk_release().

                     This function is identical  to  bpf_sk_lookup_tcp(),  except  that  it  also
                     returns timewait or request sockets. Use bpf_sk_fullsock() or bpf_tcp_sock()
                     to access the full structure.

                     This helper is available only if the kernel  was  compiled  with  CONFIG_NET
                     configuration option.

              Return Pointer  to  struct  bpf_sock, or NULL in case of failure.  For sockets with
                     reuseport option, the struct bpf_sock result is  from  reuse->socks[]  using
                     the hash of the tuple.

       long  bpf_tcp_check_syncookie(struct  bpf_sock  *sk, void *iph, u32 iph_len, struct tcphdr
       *th, u32 th_len)

              Description
                     Check whether iph and th contain a valid SYN cookie ACK  for  the  listening
                     socket in sk.

                     iph  points  to the start of the IPv4 or IPv6 header, while iph_len contains
                     sizeof(struct iphdr) or sizeof(struct ip6hdr).

                     th  points  to  the  start  of  the  TCP  header,  while   th_len   contains
                     sizeof(struct tcphdr).

              Return 0 if iph and th are a valid SYN cookie ACK, or a negative error otherwise.

       long bpf_sysctl_get_name(struct bpf_sysctl *ctx, char *buf, size_t buf_len, u64 flags)

              Description
                     Get name of sysctl in /proc/sys/ and copy it into provided by program buffer
                     buf of size buf_len.

                     The buffer is always NUL terminated, unless it's zero-sized.

                     If flags is  zero,  full  name  (e.g.  "net/ipv4/tcp_mem")  is  copied.  Use
                     BPF_F_SYSCTL_BASE_NAME flag to copy base name only (e.g. "tcp_mem").

              Return Number of character copied (not including the trailing NUL).

                     -E2BIG  if  the buffer wasn't big enough (buf will contain truncated name in
                     this case).

       long bpf_sysctl_get_current_value(struct bpf_sysctl *ctx, char *buf, size_t buf_len)

              Description
                     Get current value of sysctl as it is presented in /proc/sys (incl.  newline,
                     etc),  and  copy  it as a string into provided by program buffer buf of size
                     buf_len.

                     The whole value is copied, no matter what file position  user  space  issued
                     e.g. sys_read at.

                     The buffer is always NUL terminated, unless it's zero-sized.

              Return Number of character copied (not including the trailing NUL).

                     -E2BIG  if  the buffer wasn't big enough (buf will contain truncated name in
                     this case).

                     -EINVAL  if  current  value  was  unavailable,  e.g.   because   sysctl   is
                     uninitialized and read returns -EIO for it.

       long bpf_sysctl_get_new_value(struct bpf_sysctl *ctx, char *buf, size_t buf_len)

              Description
                     Get new value being written by user space to sysctl (before the actual write
                     happens) and copy it as a string into provided by program buffer buf of size
                     buf_len.

                     User space may write new value at file position > 0.

                     The buffer is always NUL terminated, unless it's zero-sized.

              Return Number of character copied (not including the trailing NUL).

                     -E2BIG  if  the buffer wasn't big enough (buf will contain truncated name in
                     this case).

                     -EINVAL if sysctl is being read.

       long bpf_sysctl_set_new_value(struct bpf_sysctl *ctx, const char *buf, size_t buf_len)

              Description
                     Override new value being written by user space to sysctl with value provided
                     by program in buffer buf of size buf_len.

                     buf should contain a string in same form as provided by user space on sysctl
                     write.

                     User space may write new value at file position > 0. To override  the  whole
                     sysctl value file position should be set to zero.

              Return 0 on success.

                     -E2BIG if the buf_len is too big.

                     -EINVAL if sysctl is being read.

       long bpf_strtol(const char *buf, size_t buf_len, u64 flags, long *res)

              Description
                     Convert  the initial part of the string from buffer buf of size buf_len to a
                     long integer according to the given base and save the result in res.

                     The string may begin with an arbitrary amount of white space (as  determined
                     by isspace(3)) followed by a single optional '-' sign.

                     Five  least  significant bits of flags encode base, other bits are currently
                     unused.

                     Base must be either 8, 10, 16 or 0 to detect  it  automatically  similar  to
                     user space strtol(3).

              Return Number  of characters consumed on success. Must be positive but no more than
                     buf_len.

                     -EINVAL if no valid digits were found or unsupported base was provided.

                     -ERANGE if resulting value was out of range.

       long bpf_strtoul(const char *buf, size_t buf_len, u64 flags, unsigned long *res)

              Description
                     Convert the initial part of the string from buffer buf of size buf_len to an
                     unsigned  long  integer  according  to the given base and save the result in
                     res.

                     The string may begin with an arbitrary amount of white space (as  determined
                     by isspace(3)).

                     Five  least  significant bits of flags encode base, other bits are currently
                     unused.

                     Base must be either 8, 10, 16 or 0 to detect  it  automatically  similar  to
                     user space strtoul(3).

              Return Number  of characters consumed on success. Must be positive but no more than
                     buf_len.

                     -EINVAL if no valid digits were found or unsupported base was provided.

                     -ERANGE if resulting value was out of range.

       void *bpf_sk_storage_get(struct bpf_map *map, struct bpf_sock *sk, void *value, u64 flags)

              Description
                     Get a bpf-local-storage from a sk.

                     Logically, it could be thought of getting the value from a map  with  sk  as
                     the  key.   From  this  perspective,   the  usage is not much different from
                     bpf_map_lookup_elem(map, &sk) except this helper enforces the key must be  a
                     full socket and the map must be a BPF_MAP_TYPE_SK_STORAGE also.

                     Underneath,  the  value is stored locally at sk instead of the map.  The map
                     is used as the bpf-local-storage "type". The bpf-local-storage "type"  (i.e.
                     the map) is searched against all bpf-local-storages residing at sk.

                     An  optional flags (BPF_SK_STORAGE_GET_F_CREATE) can be used such that a new
                     bpf-local-storage will be created if one does not exist.  value can be  used
                     together  with BPF_SK_STORAGE_GET_F_CREATE to specify the initial value of a
                     bpf-local-storage.  If value is NULL, the new bpf-local-storage will be zero
                     initialized.

              Return A bpf-local-storage pointer is returned on success.

                     NULL if not found or there was an error in adding a new bpf-local-storage.

       long bpf_sk_storage_delete(struct bpf_map *map, struct bpf_sock *sk)

              Description
                     Delete a bpf-local-storage from a sk.

              Return 0 on success.

                     -ENOENT if the bpf-local-storage cannot be found.

       long bpf_send_signal(u32 sig)

              Description
                     Send  signal  sig  to  the  process  of the current task.  The signal may be
                     delivered to any of this process's threads.

              Return 0 on success or successfully queued.

                     -EBUSY if work queue under nmi is full.

                     -EINVAL if sig is invalid.

                     -EPERM if no permission to send the sig.

                     -EAGAIN if bpf program can try again.

       s64 bpf_tcp_gen_syncookie(struct bpf_sock *sk, void *iph, u32 iph_len, struct tcphdr  *th,
       u32 th_len)

              Description
                     Try  to issue a SYN cookie for the packet with corresponding IP/TCP headers,
                     iph and th, on the listening socket in sk.

                     iph points to the start of the IPv4 or IPv6 header, while  iph_len  contains
                     sizeof(struct iphdr) or sizeof(struct ip6hdr).

                     th  points  to the start of the TCP header, while th_len contains the length
                     of the TCP header.

              Return On success, lower 32 bits hold the generated SYN cookie in  followed  by  16
                     bits  which  hold  the  MSS  value  for that cookie, and the top 16 bits are
                     unused.

                     On failure, the returned value is one of the following:

                     -EINVAL SYN cookie cannot be issued due to error

                     -ENOENT SYN cookie should not be issued (no SYN flood)

                     -EOPNOTSUPP kernel configuration does not enable SYN cookies

                     -EPROTONOSUPPORT IP packet version is not 4 or 6

       long bpf_skb_output(void *ctx, struct bpf_map *map, u64 flags, void *data, u64 size)

              Description
                     Write raw data blob into a special BPF  perf  event  held  by  map  of  type
                     BPF_MAP_TYPE_PERF_EVENT_ARRAY.  This  perf  event  must  have  the following
                     attributes: PERF_SAMPLE_RAW as sample_type, PERF_TYPE_SOFTWARE as type,  and
                     PERF_COUNT_SW_BPF_OUTPUT as config.

                     The  flags are used to indicate the index in map for which the value must be
                     put, masked with BPF_F_INDEX_MASK.   Alternatively,  flags  can  be  set  to
                     BPF_F_CURRENT_CPU  to indicate that the index of the current CPU core should
                     be used.

                     The value to write, of size, is passed through eBPF  stack  and  pointed  by
                     data.

                     ctx is a pointer to in-kernel struct sk_buff.

                     This   helper  is  similar  to  bpf_perf_event_output()  but  restricted  to
                     raw_tracepoint bpf programs.

              Return 0 on success, or a negative error in case of failure.

       long bpf_probe_read_user(void *dst, u32 size, const void *unsafe_ptr)

              Description
                     Safely attempt to read size bytes from user  space  address  unsafe_ptr  and
                     store the data in dst.

              Return 0 on success, or a negative error in case of failure.

       long bpf_probe_read_kernel(void *dst, u32 size, const void *unsafe_ptr)

              Description
                     Safely  attempt  to read size bytes from kernel space address unsafe_ptr and
                     store the data in dst.

              Return 0 on success, or a negative error in case of failure.

       long bpf_probe_read_user_str(void *dst, u32 size, const void *unsafe_ptr)

              Description
                     Copy a NUL terminated string from an unsafe user address unsafe_ptr to  dst.
                     The  size should include the terminating NUL byte. In case the string length
                     is smaller than size, the target is not padded with further  NUL  bytes.  If
                     the  string length is larger than size, just size-1 bytes are copied and the
                     last byte is set to NUL.

                     On success, the length of the copied string is  returned.  This  makes  this
                     helper  useful in tracing programs for reading strings, and more importantly
                     to get its length at runtime. See the following snippet:

                        SEC("kprobe/sys_open")
                        void bpf_sys_open(struct pt_regs *ctx)
                        {
                                char buf[PATHLEN]; // PATHLEN is defined to 256
                                int res = bpf_probe_read_user_str(buf, sizeof(buf),
                                                                  ctx->di);

                                // Consume buf, for example push it to
                                // userspace via bpf_perf_event_output(); we
                                // can use res (the string length) as event
                                // size, after checking its boundaries.
                        }

                     In comparison, using bpf_probe_read_user() helper here instead to  read  the
                     string would require to estimate the length at compile time, and would often
                     result in copying more memory than necessary.

                     Another useful use case is when  parsing  individual  process  arguments  or
                     individual   environment  variables  navigating  current->mm->arg_start  and
                     current->mm->env_start: using this helper and  the  return  value,  one  can
                     quickly iterate at the right offset of the memory area.

              Return On  success,  the  strictly  positive  length  of  the string, including the
                     trailing NUL character. On error, a negative value.

       long bpf_probe_read_kernel_str(void *dst, u32 size, const void *unsafe_ptr)

              Description
                     Copy a NUL terminated string from an unsafe  kernel  address  unsafe_ptr  to
                     dst. Same semantics as with bpf_probe_read_user_str() apply.

              Return On  success,  the  strictly  positive  length  of  the string, including the
                     trailing NUL character. On error, a negative value.

       long bpf_tcp_send_ack(void *tp, u32 rcv_nxt)

              Description
                     Send out a tcp-ack. tp is the in-kernel struct  tcp_sock.   rcv_nxt  is  the
                     ack_seq to be sent out.

              Return 0 on success, or a negative error in case of failure.

       long bpf_send_signal_thread(u32 sig)

              Description
                     Send signal sig to the thread corresponding to the current task.

              Return 0 on success or successfully queued.

                     -EBUSY if work queue under nmi is full.

                     -EINVAL if sig is invalid.

                     -EPERM if no permission to send the sig.

                     -EAGAIN if bpf program can try again.

       u64 bpf_jiffies64(void)

              Description
                     Obtain the 64bit jiffies

              Return The 64 bit jiffies

       long  bpf_read_branch_records(struct  bpf_perf_event_data  *ctx,  void *buf, u32 size, u64
       flags)

              Description
                     For an eBPF program attached to a perf event, retrieve  the  branch  records
                     (struct  perf_branch_entry)  associated  to  ctx  and store it in the buffer
                     pointed by buf up to size size bytes.

              Return On success, number of bytes written to buf. On error, a negative value.

                     The flags can be set to BPF_F_GET_BRANCH_RECORDS_SIZE to instead return  the
                     number  of  bytes  required to store all the branch entries. If this flag is
                     set, buf may be NULL.

                     -EINVAL if arguments  invalid  or  size  not  a  multiple  of  sizeof(struct
                     perf_branch_entry).

                     -ENOENT if architecture does not support branch records.

       long  bpf_get_ns_current_pid_tgid(u64  dev,  u64  ino,  struct bpf_pidns_info *nsdata, u32
       size)

              Description
                     Returns 0 on success, values for pid and  tgid  as  seen  from  the  current
                     namespace will be returned in nsdata.

              Return 0 on success, or one of the following in case of failure:

                     -EINVAL  if  dev  and  inum supplied don't match dev_t and inode number with
                     nsfs of current task, or if dev conversion to dev_t lost high bits.

                     -ENOENT if pidns does not exists for the current task.

       long bpf_xdp_output(void *ctx, struct bpf_map *map, u64 flags, void *data, u64 size)

              Description
                     Write raw data blob into a special BPF  perf  event  held  by  map  of  type
                     BPF_MAP_TYPE_PERF_EVENT_ARRAY.  This  perf  event  must  have  the following
                     attributes: PERF_SAMPLE_RAW as sample_type, PERF_TYPE_SOFTWARE as type,  and
                     PERF_COUNT_SW_BPF_OUTPUT as config.

                     The  flags are used to indicate the index in map for which the value must be
                     put, masked with BPF_F_INDEX_MASK.   Alternatively,  flags  can  be  set  to
                     BPF_F_CURRENT_CPU  to indicate that the index of the current CPU core should
                     be used.

                     The value to write, of size, is passed through eBPF  stack  and  pointed  by
                     data.

                     ctx is a pointer to in-kernel struct xdp_buff.

                     This   helper   is  similar  to  bpf_perf_eventoutput()  but  restricted  to
                     raw_tracepoint bpf programs.

              Return 0 on success, or a negative error in case of failure.

       u64 bpf_get_netns_cookie(void *ctx)

              Description
                     Retrieve the cookie (generated by the kernel) of the network  namespace  the
                     input  ctx  is  associated with. The network namespace cookie remains stable
                     for its lifetime and provides  a  global  identifier  that  can  be  assumed
                     unique.  If  ctx is NULL, then the helper returns the cookie for the initial
                     network  namespace.  The  cookie  itself  is  very  similar   to   that   of
                     bpf_get_socket_cookie()  helper,  but  for  network  namespaces  instead  of
                     sockets.

              Return A 8-byte long opaque number.

       u64 bpf_get_current_ancestor_cgroup_id(int ancestor_level)

              Description
                     Return id of cgroup v2 that is ancestor of the cgroup  associated  with  the
                     current  task  at  the  ancestor_level. The root cgroup is at ancestor_level
                     zero  and  each  step  down  the  hierarchy   increments   the   level.   If
                     ancestor_level  ==  level  of  cgroup associated with the current task, then
                     return value will be the same as that of bpf_get_current_cgroup_id().

                     The helper is useful to implement policies based on cgroups that  are  upper
                     in hierarchy than immediate cgroup associated with the current task.

                     The   format   of  returned  id  and  helper  limitations  are  same  as  in
                     bpf_get_current_cgroup_id().

              Return The id is returned or 0 in case the id could not be retrieved.

       long bpf_sk_assign(struct sk_buff *skb, struct bpf_sock *sk, u64 flags)

              Description
                     Helper is overloaded depending on BPF program type. This description applies
                     to BPF_PROG_TYPE_SCHED_CLS and BPF_PROG_TYPE_SCHED_ACT programs.

                     Assign   the   sk  to  the  skb.  When  combined  with  appropriate  routing
                     configuration to receive the packet towards the socket, will cause skb to be
                     delivered  to  the  specified  socket.   Subsequent  redirection  of skb via
                     bpf_redirect(), bpf_clone_redirect() or other methods  outside  of  BPF  may
                     interfere with successful delivery to the socket.

                     This operation is only valid from TC ingress path.

                     The flags argument must be zero.

              Return 0 on success, or a negative error in case of failure:

                     -EINVAL if specified flags are not supported.

                     -ENOENT if the socket is unavailable for assignment.

                     -ENETUNREACH if the socket is unreachable (wrong netns).

                     -EOPNOTSUPP  if  the  operation  is  not  supported, for example a call from
                     outside of TC ingress.

                     -ESOCKTNOSUPPORT if the socket type is not supported (reuseport).

       long bpf_sk_assign(struct bpf_sk_lookup *ctx, struct bpf_sock *sk, u64 flags)

              Description
                     Helper is overloaded depending on BPF program type. This description applies
                     to BPF_PROG_TYPE_SK_LOOKUP programs.

                     Select the sk as a result of a socket lookup.

                     For  the  operation  to  succeed  passed  socket must be compatible with the
                     packet description provided by the ctx object.

                     L4 protocol (IPPROTO_TCP or IPPROTO_UDP) must be an exact  match.  While  IP
                     family  (AF_INET  or AF_INET6) must be compatible, that is IPv6 sockets that
                     are not v6-only can be selected for IPv4 packets.

                     Only TCP listeners and UDP unconnected sockets can be selected. sk can  also
                     be NULL to reset any previous selection.

                     flags argument can combination of following values:

                     · BPF_SK_LOOKUP_F_REPLACE   to   override  the  previous  socket  selection,
                       potentially done by a BPF program that ran before us.

                     · BPF_SK_LOOKUP_F_NO_REUSEPORT to skip load-balancing within reuseport group
                       for the socket being selected.

                     On success ctx->sk will point to the selected socket.

              Return 0 on success, or a negative errno in case of failure.

                     · -EAFNOSUPPORT  if socket family (sk->family) is not compatible with packet
                       family (ctx->family).

                     · -EEXIST if socket  has  been  already  selected,  potentially  by  another
                       program, and BPF_SK_LOOKUP_F_REPLACE flag was not specified.

                     · -EINVAL if unsupported flags were specified.

                     · -EPROTOTYPE  if  socket  L4  protocol  (sk->protocol) doesn't match packet
                       protocol (ctx->protocol).

                     · -ESOCKTNOSUPPORT if socket is not in allowed state (TCP listening  or  UDP
                       unconnected).

       u64 bpf_ktime_get_boot_ns(void)

              Description
                     Return the time elapsed since system boot, in nanoseconds.  Does include the
                     time the system was suspended.  See: clock_gettime(CLOCK_BOOTTIME)

              Return Current ktime.

       long bpf_seq_printf(struct seq_file *m, const char *fmt, u32 fmt_size, const  void  *data,
       u32 data_len)

              Description
                     bpf_seq_printf()  uses seq_file seq_printf() to print out the format string.
                     The m represents the seq_file. The fmt  and  fmt_size  are  for  the  format
                     string  itself.  The data and data_len are format string arguments. The data
                     are a u64 array and corresponding format string values  are  stored  in  the
                     array.  For  strings  and  pointers  where  pointees  are accessed, only the
                     pointer values are stored in the data array.  The data_len is  the  size  of
                     data in bytes.

                     Formats  %s,  %p{i,I}{4,6}  requires  to read kernel memory.  Reading kernel
                     memory may fail due to either invalid address or valid address but requiring
                     a major memory fault. If reading kernel memory fails, the string for %s will
                     be an empty string, and the ip address  for  %p{i,I}{4,6}  will  be  0.  Not
                     returning  error  to  bpf program is consistent with what bpf_trace_printk()
                     does for now.

              Return 0 on success, or a negative error in case of failure:

                     -EBUSY if per-CPU memory copy buffer is busy, can try again by  returning  1
                     from bpf program.

                     -EINVAL if arguments are invalid, or if fmt is invalid/unsupported.

                     -E2BIG if fmt contains too many format specifiers.

                     -EOVERFLOW if an overflow happened: The same object will be tried again.

       long bpf_seq_write(struct seq_file *m, const void *data, u32 len)

              Description
                     bpf_seq_write()  uses  seq_file  seq_write()  to  write  the  data.   The  m
                     represents the seq_file. The data and len represent the  data  to  write  in
                     bytes.

              Return 0 on success, or a negative error in case of failure:

                     -EOVERFLOW if an overflow happened: The same object will be tried again.

       u64 bpf_sk_cgroup_id(struct bpf_sock *sk)

              Description
                     Return the cgroup v2 id of the socket sk.

                     sk  must  be  a  non-NULL  pointer  to a full socket, e.g. one returned from
                     bpf_sk_lookup_xxx(), bpf_sk_fullsock(), etc. The format of  returned  id  is
                     same as in bpf_skb_cgroup_id().

                     This  helper  is  available  only  if  the  kernel  was  compiled  with  the
                     CONFIG_SOCK_CGROUP_DATA configuration option.

              Return The id is returned or 0 in case the id could not be retrieved.

       u64 bpf_sk_ancestor_cgroup_id(struct bpf_sock *sk, int ancestor_level)

              Description
                     Return id of cgroup v2 that is ancestor of cgroup associated with the sk  at
                     the ancestor_level.  The root cgroup is at ancestor_level zero and each step
                     down the hierarchy increments the  level.  If  ancestor_level  ==  level  of
                     cgroup  associated  with  sk,  then  return  value  will  be same as that of
                     bpf_sk_cgroup_id().

                     The helper is useful to implement policies based on cgroups that  are  upper
                     in hierarchy than immediate cgroup associated with sk.

                     The   format   of  returned  id  and  helper  limitations  are  same  as  in
                     bpf_sk_cgroup_id().

              Return The id is returned or 0 in case the id could not be retrieved.

       long bpf_ringbuf_output(void *ringbuf, void *data, u64 size, u64 flags)

              Description
                     Copy size bytes from data into a ring buffer ringbuf.   If  BPF_RB_NO_WAKEUP
                     is specified in flags, no notification of new data availability is sent.  If
                     BPF_RB_FORCE_WAKEUP  is  specified  in  flags,  notification  of  new   data
                     availability is sent unconditionally.

              Return 0 on success, or a negative error in case of failure.

       void *bpf_ringbuf_reserve(void *ringbuf, u64 size, u64 flags)

              Description
                     Reserve size bytes of payload in a ring buffer ringbuf.

              Return Valid pointer with size bytes of memory available; NULL, otherwise.

       void bpf_ringbuf_submit(void *data, u64 flags)

              Description
                     Submit reserved ring buffer sample, pointed to by data.  If BPF_RB_NO_WAKEUP
                     is specified in flags, no notification of new data availability is sent.  If
                     BPF_RB_FORCE_WAKEUP   is  specified  in  flags,  notification  of  new  data
                     availability is sent unconditionally.

              Return Nothing. Always succeeds.

       void bpf_ringbuf_discard(void *data, u64 flags)

              Description
                     Discard  reserved  ring   buffer   sample,   pointed   to   by   data.    If
                     BPF_RB_NO_WAKEUP  is  specified  in  flags,  no  notification  of  new  data
                     availability  is  sent.   If  BPF_RB_FORCE_WAKEUP  is  specified  in  flags,
                     notification of new data availability is sent unconditionally.

              Return Nothing. Always succeeds.

       u64 bpf_ringbuf_query(void *ringbuf, u64 flags)

              Description
                     Query  various  characteristics  of  provided  ring  buffer. What exactly is
                     queries is determined by flags:

                     · BPF_RB_AVAIL_DATA: Amount of data not yet consumed.

                     · BPF_RB_RING_SIZE: The size of ring buffer.

                     · BPF_RB_CONS_POS: Consumer position (can wrap around).

                     · BPF_RB_PROD_POS: Producer(s) position (can wrap around).

                     Data returned is just a momentary snapshot of actual  values  and  could  be
                     inaccurate,  so  this  facility  should  be used to power heuristics and for
                     reporting, not to make 100% correct calculation.

              Return Requested value, or 0, if flags are not recognized.

       long bpf_csum_level(struct sk_buff *skb, u64 level)

              Description
                     Change the skbs checksum level by one layer up or down, or reset it entirely
                     to none in order to have the stack perform checksum validation. The level is
                     applicable to the following  protocols:  TCP,  UDP,  GRE,  SCTP,  FCOE.  For
                     example,  a  decap  of | ETH | IP | UDP | GUE | IP | TCP | into | ETH | IP |
                     TCP   |   through   bpf_skb_adjust_room()    helper    with    passing    in
                     BPF_F_ADJ_ROOM_NO_CSUM_RESET flag would require one call to bpf_csum_level()
                     with BPF_CSUM_LEVEL_DEC since the UDP header is removed. Similarly, an encap
                     of  the  latter  into  the  former  could be accompanied by a helper call to
                     bpf_csum_level() with BPF_CSUM_LEVEL_INC if the skb is still intended to  be
                     processed in higher layers of the stack instead of just egressing at tc.

                     There are three supported level settings at this time:

                     · BPF_CSUM_LEVEL_INC:    Increases    skb->csum_level    for    skbs    with
                       CHECKSUM_UNNECESSARY.

                     · BPF_CSUM_LEVEL_DEC:    Decreases    skb->csum_level    for    skbs    with
                       CHECKSUM_UNNECESSARY.

                     · BPF_CSUM_LEVEL_RESET:  Resets  skb->csum_level to 0 and sets CHECKSUM_NONE
                       to force checksum validation by the stack.

                     · BPF_CSUM_LEVEL_QUERY: No-op, returns the current skb->csum_level.

              Return 0 on success, or a negative error  in  case  of  failure.  In  the  case  of
                     BPF_CSUM_LEVEL_QUERY,  the  current skb->csum_level is returned or the error
                     code -EACCES in case the skb is not subject to CHECKSUM_UNNECESSARY.

       struct tcp6_sock *bpf_skc_to_tcp6_sock(void *sk)

              Description
                     Dynamically cast a sk pointer to a tcp6_sock pointer.

              Return sk if casting is valid, or NULL otherwise.

       struct tcp_sock *bpf_skc_to_tcp_sock(void *sk)

              Description
                     Dynamically cast a sk pointer to a tcp_sock pointer.

              Return sk if casting is valid, or NULL otherwise.

       struct tcp_timewait_sock *bpf_skc_to_tcp_timewait_sock(void *sk)

              Description
                     Dynamically cast a sk pointer to a tcp_timewait_sock pointer.

              Return sk if casting is valid, or NULL otherwise.

       struct tcp_request_sock *bpf_skc_to_tcp_request_sock(void *sk)

              Description
                     Dynamically cast a sk pointer to a tcp_request_sock pointer.

              Return sk if casting is valid, or NULL otherwise.

       struct udp6_sock *bpf_skc_to_udp6_sock(void *sk)

              Description
                     Dynamically cast a sk pointer to a udp6_sock pointer.

              Return sk if casting is valid, or NULL otherwise.

       long bpf_get_task_stack(struct task_struct *task, void *buf, u32 size, u64 flags)

              Description
                     Return a user or a kernel stack in bpf program provided buffer.  To  achieve
                     this, the helper needs task, which is a valid pointer to struct task_struct.
                     To store the stacktrace, the bpf program provides  buf  with  a  nonnegative
                     size.

                     The  last  argument, flags, holds the number of stack frames to skip (from 0
                     to 255), masked with BPF_F_SKIP_FIELD_MASK. The next bits can be used to set
                     the following flags:

                     BPF_F_USER_STACK
                            Collect a user space stack instead of a kernel stack.

                     BPF_F_USER_BUILD_ID
                            Collect  buildid+offset  instead of ips for user stack, only valid if
                            BPF_F_USER_STACK is also specified.

                     bpf_get_task_stack() can collect up to PERF_MAX_STACK_DEPTH both kernel  and
                     user  frames,  subject to sufficient large buffer size. Note that this limit
                     can be controlled with the sysctl program, and that it  should  be  manually
                     increased  in  order  to  profile  long user stacks (such as stacks for Java
                     programs). To do so, use:

                        # sysctl kernel.perf_event_max_stack=<new value>

              Return A non-negative value equal to or less than size on success,  or  a  negative
                     error in case of failure.

EXAMPLES

       Example usage for most of the eBPF helpers listed in this manual page are available within
       the Linux kernel sources, at the following locations:

       · samples/bpf/

       · tools/testing/selftests/bpf/

LICENSE

       eBPF programs can have an associated license, passed along with the bytecode  instructions
       to the kernel when the programs are loaded. The format for that string is identical to the
       one in use for kernel modules (Dual licenses, such as "Dual BSD/GPL", may be  used).  Some
       helper  functions are only accessible to programs that are compatible with the GNU Privacy
       License (GPL).

       In order to use such helpers, the eBPF program must be loaded  with  the  correct  license
       string  passed (via attr) to the bpf() system call, and this generally translates into the
       C source code of the program containing a line similar to the following:

          char ____license[] __attribute__((section("license"), used)) = "GPL";

IMPLEMENTATION

       This manual page is an effort to document the existing eBPF helper functions.  But  as  of
       this writing, the BPF sub-system is under heavy development. New eBPF program or map types
       are added, along with new helper functions. Some helpers are occasionally  made  available
       for additional program types. So in spite of the efforts of the community, this page might
       not be up-to-date. If you want to check by yourself what helper functions  exist  in  your
       kernel,  or  what types of programs they can support, here are some files among the kernel
       tree that you may be interested in:

       · include/uapi/linux/bpf.h is the main BPF header. It contains the full list of all helper
         functions, as well as many other BPF definitions including most of the flags, structs or
         constants used by the helpers.

       · net/core/filter.c contains the definition of most network-related helper functions,  and
         the list of program types from which they can be used.

       · kernel/trace/bpf_trace.c is the equivalent for most tracing program-related helpers.

       · kernel/bpf/verifier.c contains the functions used to check that valid types of eBPF maps
         are used with a given helper function.

       · kernel/bpf/ directory contains other files in which additional helpers are defined  (for
         cgroups, sockmaps, etc.).

       · The  bpftool  utility  can  be used to probe the availability of helper functions on the
         system (as well as supported program and map types, and a number of  other  parameters).
         To  do  so,  run  bpftool  feature  probe  (see bpftool-feature(8) for details). Add the
         unprivileged keyword to list features available to unprivileged users.

       Compatibility between helper functions and program types can generally  be  found  in  the
       files  where  helper functions are defined. Look for the struct bpf_func_proto objects and
       for functions returning them: these functions contain a  list  of  helpers  that  a  given
       program  type can call. Note that the default: label of the switch ... case used to filter
       helpers can call other functions, themselves allowing access to  additional  helpers.  The
       requirement for GPL license is also in those struct bpf_func_proto.

       Compatibility   between   helper   functions   and   map   types   can  be  found  in  the
       check_map_func_compatibility() function in file kernel/bpf/verifier.c.

       Helper functions that invalidate the checks on data  and  data_end  pointers  for  network
       processing are listed in function bpf_helper_changes_pkt_data() in file net/core/filter.c.

SEE ALSO

       bpf(2),   bpftool(8),   cgroups(7),   ip(8),  perf_event_open(2),  sendmsg(2),  socket(7),
       tc-bpf(8)

COLOPHON

       This page is part of release 5.10 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at https://www.kernel.org/doc/man-pages/.

                                                                                   BPF-HELPERS(7)