netisr_dispatch (9)

Leading comments

Copyright (c) 2009 Robert N. M. Watson
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(The comments found at the beginning of the groff file "man9/netisr_dispatch.9freebsd".)

NAME

netisr - Kernel network dispatch service

SYNOPSIS

In net/netisr.h Ft void Fn netisr_register const struct netisr_handler *nhp Ft void Fn netisr_unregister const struct netisr_handler *nhp Ft int Fn netisr_dispatch u_int proto struct mbuf *m Ft int Fn netisr_dispatch_src u_int proto uintptr_t source struct mbuf *m Ft int Fn netisr_queue u_int proto struct mbuf *m Ft int Fn netisr_queue_src u_int proto uintptr_t source struct mbuf *m Ft void Fn netisr_clearqdrops const struct netisr_handler *nhp Ft void Fn netisr_getqdrops const struct netisr_handler *nhp uint64_t *qdropsp Ft void Fn netisr_getqlimit const struct netisr_handler *nhp u_int *qlimitp Ft int Fn netisr_setqlimit const struct netisr_handler *nhp u_int qlimit Ft u_int Fn netisr_default_flow2cpu u_int flowid Ft u_int Fn netisr_get_cpucount void Ft u_int Fn netisr_get_cpuid u_int cpunumber

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

options VIMAGE

Ft void Fn netisr_register_vnet const struct netisr_handler *nhp Ft void Fn netisr_unregister_vnet const struct netisr_handler *nhp

DESCRIPTION

The 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 Fn netisr_register and Fn netisr_unregister , and may also manage queue limits and statistics using the Fn netisr_clearqdrops , Fn netisr_getqdrops , Fn netisr_getqlimit , and Fn netisr_setqlimit .

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

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

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

NETISR_POLICY_FLOW

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

NETISR_POLICY_CPU

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

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

Vt const char * nh_name

Unique character string name of the protocol, which may be included in sysctl(3) MIB names, so should not contain whitespace.

Vt netisr_handler_t nh_handler

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

Vt netisr_m2flow_t nh_m2flow

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

Vt 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

Vt 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.

Vt u_int nh_proto

Protocol number used by both protocols to identify themselves to , 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.

Vt 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.

Vt 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 Fn netisr_dispatch and Fn netisr_queue interfaces. Both accept a protocol number and Vt mbuf argument, but while Fn netisr_queue will always execute the protocol handler asynchronously in a deferred context, Fn 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 Fn netisr_dispatch_src and Fn 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_ARP

ARP

NETISR_IPV6

IPv6

NETISR_NATM

ATM

NETISR_EPAIR

netstat(1), epair(4)

AUTHORS

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