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

     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);

     With optional virtual network stack support enabled via the following
     kernel compile option:

	   options VIMAGE

     netisr_register_vnet(const	struct netisr_handler *nhp);

     netisr_unregister_vnet(const struct netisr_handler	*nhp);

     The netisr	kernel interface suite allows device drivers (and other	packet
     sources) to direct	packets	to protocols for directly dispatched or	de-
     ferred 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 us-
     ing the netisr_clearqdrops(), netisr_getqdrops(), netisr_getqlimit(), and

     In	case of	VIMAGE kernels each virtual network stack (vnet), that is not
     the default base system network stack, calls netisr_register_vnet() and
     netisr_unregister_vnet() to enable	or disable packet processing by	the
     netisr for	each protocol.	Disabling will also purge any outstanding
     packet from the protocol queue.

     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 poli-

     NETISR_POLICY_SOURCE  netisr should maintain source ordering without ad-
			   vice	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 im-
			   plements nh_m2flow, then netisr will	query the pro-
			   tocol 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 proto-
				  col, which may be included in	sysctl(3) MIB
				  names, so should not contain whitespace.

     netisr_handler_t nh_handler  Protocol handler function that will be in-
				  voked	on each	packet received	for the	proto-

     netisr_m2flow_t nh_m2flow	  Optional protocol function to	generate a
				  flow ID and set a valid hashtype for packets
				  that enter the netisr	with M_HASHTYPE_GET(m)
				  equal	to M_HASHTYPE_NONE.  Will be used only

     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 in-
				  voked	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	de-
				  tails, 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 ac-
     cept 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_IPV6   IPv6

     NETISR_EPAIR  netstat(1), epair(4)

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

FreeBSD	13.0			April 25, 2017			  FreeBSD 13.0


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