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     netisr — Kernel network dispatch service


     #include <net/netisr.h>

     netisr_register(const struct netisr_handler *nhp);

     netisr_unregister(const struct netisr_handler *nhp);

     netisr_dispatch(u_int proto, struct mbuf *m);

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

     netisr_queue(u_int proto, struct mbuf *m);

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

     netisr_clearqdrops(const struct netisr_handler *nhp);

     netisr_getqdrops(const struct netisr_handler *nhp, uint64_t *qdropsp);

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

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

     netisr_default_flow2cpu(u_int flowid);


     netisr_get_cpuid(u_int cpunumber);


     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 to
     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

     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_IPV6    IPv6


     NETISR_EPAIR   netstat(1), epair(4)


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