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NETISR(9) FreeBSD 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, uint64_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);
With optional virtual network stack support enabled via the following
kernel compile option:
options VIMAGE
void
netisr_register_vnet(const struct netisr_handler *nhp);
void
netisr_unregister_vnet(const struct netisr_handler *nhp);
DESCRIPTION
The netisr kernel interface suite allows device drivers (and other packet
using the netisr_clearqdrops(), netisr_getqdrops(), netisr_getqlimit(),
and netisr_setqlimit().
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
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(3)
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 a valid hashtype for packets
that enter the netisr with M_HASHTYPE_GET(m)
equal to M_HASHTYPE_NONE. 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
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_ARP ARP
NETISR_IPV6 IPv6
AUTHORS
This manual page and the netisr implementation were written by Robert N.
M. Watson.
FreeBSD 14.0-RELEASE-p6 April 12, 2023 FreeBSD 14.0-RELEASE-p6