NAME

       netisr — Kernel network dispatch service

SYNOPSIS

       #include <net/netisr.h>

       void
       netisr_register(const struct netisr_handler *nhp);

       void
       netisr_unregister(const struct netisr_handler *nhp);

       int
       netisr_dispatch(u_int proto, struct mbuf *m);

       int
       netisr_dispatch_src(u_int proto, uintptr_t source, struct mbuf *m);

       int
       netisr_queue(u_int proto, struct mbuf *m);

       int
       netisr_queue_src(u_int proto, uintptr_t source, struct mbuf *m);

       void
       netisr_clearqdrops(const struct netisr_handler *nhp);

       void
       netisr_getqdrops(const struct netisr_handler *nhp, u_int64_t *qdropsp);

       void
       netisr_getqlimit(const struct netisr_handler *nhp, u_int *qlimitp);

       int
       netisr_setqlimit(const struct netisr_handler *nhp, u_int qlimit);

       u_int
       netisr_default_flow2cpu(u_int flowid);

       u_int
       netisr_get_cpucount(void);

       u_int
       netisr_get_cpuid(u_int cpunumber);

DESCRIPTION

       The  netisr  kernel interface suite allows device drivers (and other packet sources) to direct packets to
       protocols for directly  dispatched  or  deferred  processing.   Protocol  registration  and  work  stream
       statistics may be monitored using netstat(1).

   Protocol registration
       Protocols  register and unregister handlers using netisr_register() and netisr_unregister(), and may also
       manage   queue   limits   and   statistics   using    the    netisr_clearqdrops(),    netisr_getqdrops(),
       netisr_getqlimit(), and netisr_setqlimit().

       netisr supports multi-processor execution of handlers, and relies on a combination of source ordering and
       protocol-specific  ordering  and  work-placement  policies to decide how do distribute work across one or
       more worker threads.  Registering protocols will declare one of three policies:

       NETISR_POLICY_SOURCE  netisr should maintain source ordering without advice from  the  protocol.   netisr
                             will  ignore  any  flow  IDs  present  on  mbuf  headers  for  the purposes of work
                             placement.

       NETISR_POLICY_FLOW    netisr should maintain flow ordering as defined by the mbuf header flow  ID  field.
                             If  the  protocol  implements nh_m2flow, then netisr will query the protocol in the
                             event that the mbuf doesn't have a flow ID, falling back on source ordering.

       NETISR_POLICY_CPU     netisr will entirely  delegate  all  work  placement  decisions  to  the  protocol,
                             querying nh_m2cpuid for each packet.

       Registration is declared using struct netisr_handler, whose fields are defined as follows:

       const char * nh_name         Unique  character  string  name  of  the  protocol, which may be included in
                                    sysctl(2) MIB names, so should not contain whitespace.

       netisr_handler_t nh_handler  Protocol handler function that will be invoked on each packet  received  for
                                    the protocol.

       netisr_m2flow_t nh_m2flow    Optional  protocol  function  to  generate  a  flow  ID and set M_FLOWID for
                                    packets that do not enter netisr with M_FLOWID defined.  Will be  used  only
                                    with NETISR_POLICY_FLOW.

       netisr_m2cpuid_t nh_m2cpuid  Protocol  function  to  determine  what CPU a packet should be processed on.
                                    Will be used only with NETISR_POLICY_CPU.

       netisr_drainedcpu_t nh_drainedcpu
                                    Optional callback function that will be invoked when  a  per-CPU  queue  was
                                    drained.   It will never fire for directly dispatched packets.  Unless fully
                                    understood, this special-purpose function should not be used.

       u_int nh_proto               Protocol number used by both protocols to identify themselves to netisr, and
                                    by packet sources to select what handler will be used to process packets.  A
                                    table of supported  protocol  numbers  appears  below.   For  implementation
                                    reasons, protocol numbers great than 15 are currently unsupported.

       u_int nh_qlimit              The   maximum  per-CPU  queue  depth  for  the  protocol;  due  to  internal
                                    implementation details, the effective queue depth may be as  much  as  twice
                                    this number.

       u_int nh_policy              The  ordering  and  work  placement  policy  for  the protocol, as described
                                    earlier.

   Packet source interface
       Packet sources, such as network interfaces, may request protocol processing using  the  netisr_dispatch()
       and netisr_queue() interfaces.  Both accept a protocol number and mbuf argument, but while netisr_queue()
       will  always  execute  the  protocol handler asynchronously in a deferred context, netisr_dispatch() will
       optionally direct dispatch if permitted by global and per-protocol policy.

       In order to provide additional load balancing and flow information, packet sources may  also  specify  an
       opaque  source identifier, which in practice might be a network interface number or socket pointer, using
       the netisr_dispatch_src() and netisr_queue_src() variants.

   Protocol number constants
       The follow protocol numbers are currently defined:

       NETISR_IP      IPv4

       NETISR_IGMP    IGMPv3 loopback

       NETISR_ROUTE   Routing socket loopback

       NETISR_AARP    Appletalk AARP

       NETISR_ATALK1  Appletalk phase 1

       NETISR_ATALK2  Appletalk phase 2

       NETISR_ARP     ARP

       NETISR_IPX     IPX/SPX

       NETISR_IPV6    IPv6

       NETISR_NATM    ATM

       NETISR_EPAIR   netstat(1), epair(4)

AUTHORS

       This manual page and the netisr implementation were written by Robert N. M. Watson.

Debian                                          February 22, 2010                                      NETISR(9)