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NETISR(9) 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 sources) to direct packets to protocols for directly dispatched or deferred processing. Protocol registration and work stream statis- tics 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 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 outstand- ing 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- cies: 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 proto- col 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 proto- col, which may be included in sysctl(3) MIB names, so should not contain white- space. netisr_handler_t nh_handler Protocol handler function that will be in- voked on each packet received for the pro- tocol. netisr_m2flow_t nh_m2flow Optional protocol function to generate a flow ID and set a valid hashtype for pack- ets 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 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 num- bers great than 15 are currently unsup- ported. 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 pro- cessing 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 dis- patch 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 14.3 April 12, 2023 NETISR(9)
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