NETISR(9) BSD Kernel Developer's Manual NETISR(9)
netisr -- Kernel network dispatch service
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);
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 and work stream statistics may be monitored using netstat(1).
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 to distribute work across one or more worker threads. Registering protocols will declare one of three
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
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(2) MIB names, so should not con-
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
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 implementa-
tion 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 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_IGMP IGMPv3 loopback
NETISR_ROUTE Routing socket loopback
NETISR_EPAIR netstat(1), epair(4)
This manual page and the netisr implementation were written by Robert N. M. Watson.
January 11, 2015 BSD