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NETISR(9)		 BSD Kernel Developer's Manual		     NETISR(9)

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
     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 poli‐
     cies:

     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 evet 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 proto‐
				  col, which may be included in 2(sysctl) 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 pro‐
				  tocol.

     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 spe‐
				  cial-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 imple‐
				  mentation reasons, protocol numbers great
				  than 15 are currently unsupported.

     u_int nh_qlimit		  The maximum per-CPU queue depth for the pro‐
				  tocol; 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 process‐
     ing 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 asynchonously 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   epair(4)

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

BSD				 July 26, 2009				   BSD
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