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 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 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 protocol, 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 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 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.