xref: /freebsd/share/man/man9/ifnet.9 (revision 273c26a3c3bea87a241d6879abd4f991db180bf0)
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31.Dd September 27, 2016
32.Dt IFNET 9
33.Os
34.Sh NAME
35.Nm ifnet ,
36.Nm ifaddr ,
37.Nm ifqueue ,
38.Nm if_data
39.Nd kernel interfaces for manipulating network interfaces
40.Sh SYNOPSIS
41.In sys/param.h
42.In sys/time.h
43.In sys/socket.h
44.In net/if.h
45.In net/if_var.h
46.In net/if_types.h
47.\"
48.Ss "Interface Manipulation Functions"
49.Ft "struct ifnet *"
50.Fn if_alloc "u_char type"
51.Ft void
52.Fn if_attach "struct ifnet *ifp"
53.Ft void
54.Fn if_detach "struct ifnet *ifp"
55.Ft void
56.Fn if_free "struct ifnet *ifp"
57.Ft void
58.Fn if_free_type "struct ifnet *ifp" "u_char type"
59.Ft void
60.Fn if_down "struct ifnet *ifp"
61.Ft int
62.Fn ifioctl "struct socket *so" "u_long cmd" "caddr_t data" "struct thread *td"
63.Ft int
64.Fn ifpromisc "struct ifnet *ifp" "int pswitch"
65.Ft int
66.Fn if_allmulti "struct ifnet *ifp" "int amswitch"
67.Ft "struct ifnet *"
68.Fn ifunit "const char *name"
69.Ft "struct ifnet *"
70.Fn ifunit_ref "const char *name"
71.Ft void
72.Fn if_up "struct ifnet *ifp"
73.\"
74.Ss "Interface Address Functions"
75.Ft "struct ifaddr *"
76.Fn ifaddr_byindex "u_short idx"
77.Ft "struct ifaddr *"
78.Fn ifa_ifwithaddr "struct sockaddr *addr"
79.Ft "struct ifaddr *"
80.Fn ifa_ifwithdstaddr "struct sockaddr *addr" "int fib"
81.Ft "struct ifaddr *"
82.Fn ifa_ifwithnet "struct sockaddr *addr" "int ignore_ptp" "int fib"
83.Ft "struct ifaddr *"
84.Fn ifaof_ifpforaddr "struct sockaddr *addr" "struct ifnet *ifp"
85.Ft void
86.Fn ifa_ref "struct ifaddr *ifa"
87.Ft void
88.Fn ifa_free "struct ifaddr *ifa"
89.\"
90.Ss "Interface Multicast Address Functions"
91.Ft int
92.Fn if_addmulti "struct ifnet *ifp" "struct sockaddr *sa" "struct ifmultiaddr **ifmap"
93.Ft int
94.Fn if_delmulti "struct ifnet *ifp" "struct sockaddr *sa"
95.Ft "struct ifmultiaddr *"
96.Fn if_findmulti "struct ifnet *ifp" "struct sockaddr *sa"
97.Ss "Output queue macros"
98.Fn IF_DEQUEUE "struct ifqueue *ifq" "struct mbuf *m"
99.\"
100.Ss "struct ifnet Member Functions"
101.Ft void
102.Fn \*(lp*if_input\*(rp "struct ifnet *ifp" "struct mbuf *m"
103.Ft int
104.Fo \*(lp*if_output\*(rp
105.Fa "struct ifnet *ifp" "struct mbuf *m"
106.Fa "const struct sockaddr *dst" "struct route *ro"
107.Fc
108.Ft void
109.Fn \*(lp*if_start\*(rp "struct ifnet *ifp"
110.Ft int
111.Fn \*(lp*if_transmit\*(rp "struct ifnet *ifp" "struct mbuf *m"
112.Ft void
113.Fn \*(lp*if_qflush\*(rp "struct ifnet *ifp"
114.Ft int
115.Fn \*(lp*if_ioctl\*(rp "struct ifnet *ifp" "u_long cmd" "caddr_t data"
116.Ft void
117.Fn \*(lp*if_init\*(rp "void *if_softc"
118.Ft int
119.Fo \*(lp*if_resolvemulti\*(rp
120.Fa "struct ifnet *ifp" "struct sockaddr **retsa" "struct sockaddr *addr"
121.Fc
122.Ss "struct ifaddr member function"
123.Ft void
124.Fo \*(lp*ifa_rtrequest\*(rp
125.Fa "int cmd" "struct rtentry *rt" "struct rt_addrinfo *info"
126.Fc
127.\"
128.Ss "Global Variables"
129.Vt extern struct ifnethead ifnet ;
130.\" extern struct ifindex_entry *ifindex_table ;
131.Vt extern int if_index ;
132.Vt extern int ifqmaxlen ;
133.Sh DATA STRUCTURES
134The kernel mechanisms for handling network interfaces reside primarily
135in the
136.Vt ifnet , if_data , ifaddr ,
137and
138.Vt ifmultiaddr
139structures in
140.In net/if.h
141and
142.In net/if_var.h
143and the functions named above and defined in
144.Pa /sys/net/if.c .
145Those interfaces which are intended to be used by user programs
146are defined in
147.In net/if.h ;
148these include the interface flags, the
149.Vt if_data
150structure, and the structures defining the appearance of
151interface-related messages on the
152.Xr route 4
153routing socket and in
154.Xr sysctl 3 .
155The header file
156.In net/if_var.h
157defines the kernel-internal interfaces, including the
158.Vt ifnet , ifaddr ,
159and
160.Vt ifmultiaddr
161structures and the functions which manipulate them.
162(A few user programs will need
163.In net/if_var.h
164because it is the prerequisite of some other header file like
165.In netinet/if_ether.h .
166Most references to those two files in particular can be replaced by
167.In net/ethernet.h . )
168.Pp
169The system keeps a linked list of interfaces using the
170.Li TAILQ
171macros defined in
172.Xr queue 3 ;
173this list is headed by a
174.Vt "struct ifnethead"
175called
176.Va ifnet .
177The elements of this list are of type
178.Vt "struct ifnet" ,
179and most kernel routines which manipulate interface as such accept or
180return pointers to these structures.
181Each interface structure
182contains an
183.Vt if_data
184structure used for statistics and information.
185Each interface also has a
186.Li TAILQ
187of interface addresses, described by
188.Vt ifaddr
189structures.
190An
191.Dv AF_LINK
192address
193(see
194.Xr link_addr 3 )
195describing the link layer implemented by the interface (if any)
196is accessed by the
197.Fn ifaddr_byindex
198function or
199.Va if_addr
200structure.
201(Some trivial interfaces do not provide any link layer addresses;
202this structure, while still present, serves only to identify the
203interface name and index.)
204.Pp
205Finally, those interfaces supporting reception of multicast datagrams
206have a
207.Li TAILQ
208of multicast group memberships, described by
209.Vt ifmultiaddr
210structures.
211These memberships are reference-counted.
212.Pp
213Interfaces are also associated with an output queue, defined as a
214.Vt "struct ifqueue" ;
215this structure is used to hold packets while the interface is in the
216process of sending another.
217.Pp
218.Ss The ifnet Structure
219The fields of
220.Vt "struct ifnet"
221are as follows:
222.Bl -tag -width ".Va if_capabilities" -offset indent
223.It Va if_softc
224.Pq Vt "void *"
225A pointer to the driver's private state block.
226(Initialized by driver.)
227.It Va if_l2com
228.Pq Vt "void *"
229A pointer to the common data for the interface's layer 2 protocol.
230(Initialized by
231.Fn if_alloc . )
232.It Va if_vnet
233.Pq Vt "struct vnet *"
234A pointer to the virtual network stack instance.
235(Initialized by
236.Fn if_attach . )
237.It Va if_home_vnet
238.Pq Vt "struct vnet *"
239A pointer to the parent virtual network stack, where this
240.Vt "struct ifnet"
241originates from.
242(Initialized by
243.Fn if_attach . )
244.It Va if_link
245.Pq Fn TAILQ_ENTRY ifnet
246.Xr queue 3
247macro glue.
248.It Va if_xname
249.Pq Vt "char *"
250The name of the interface,
251(e.g.,
252.Dq Li fxp0
253or
254.Dq Li lo0 ) .
255(Initialized by driver
256(usually via
257.Fn if_initname ) . )
258.It Va if_dname
259.Pq Vt "const char *"
260The name of the driver.
261(Initialized by driver
262(usually via
263.Fn if_initname ) . )
264.It Va if_dunit
265.Pq Vt int
266A unique number assigned to each interface managed by a particular
267driver.
268Drivers may choose to set this to
269.Dv IF_DUNIT_NONE
270if a unit number is not associated with the device.
271(Initialized by driver
272(usually via
273.Fn if_initname ) . )
274.It Va if_refcount
275.Pq Vt u_int
276The reference count.
277(Initialized by
278.Fn if_alloc . )
279.It Va if_addrhead
280.Pq Vt "struct ifaddrhead"
281The head of the
282.Xr queue 3
283.Li TAILQ
284containing the list of addresses assigned to this interface.
285.It Va if_pcount
286.Pq Vt int
287A count of promiscuous listeners on this interface, used to
288reference-count the
289.Dv IFF_PROMISC
290flag.
291.It Va if_carp
292.Pq Vt "struct carp_if *"
293A pointer to the CARP interface structure,
294.Xr carp 4 .
295(Initialized by the driver-specific
296.Fn if_ioctl
297routine.)
298.It Va if_bpf
299.Pq Vt "struct bpf_if *"
300Opaque per-interface data for the packet filter,
301.Xr bpf 4 .
302(Initialized by
303.Fn bpf_attach . )
304.It Va if_index
305.Pq Vt u_short
306A unique number assigned to each interface in sequence as it is
307attached.
308This number can be used in a
309.Vt "struct sockaddr_dl"
310to refer to a particular interface by index
311(see
312.Xr link_addr 3 ) .
313(Initialized by
314.Fn if_alloc . )
315.It Va if_vlantrunk
316.Pq Vt struct ifvlantrunk *
317A pointer to 802.1Q trunk structure,
318.Xr vlan 4 .
319(Initialized by the driver-specific
320.Fn if_ioctl
321routine.)
322.It Va if_flags
323.Pq Vt int
324Flags describing operational parameters of this interface (see below).
325(Manipulated by generic code.)
326.It Va if_drv_flags
327.Pq Vt int
328Flags describing operational status of this interface (see below).
329(Manipulated by driver.)
330.It Va if_capabilities
331.Pq Vt int
332Flags describing the capabilities the interface supports (see below).
333.It Va if_capenable
334.Pq Vt int
335Flags describing the enabled capabilities of the interface (see below).
336.It Va if_linkmib
337.Pq Vt "void *"
338A pointer to an interface-specific MIB structure exported by
339.Xr ifmib 4 .
340(Initialized by driver.)
341.It Va if_linkmiblen
342.Pq Vt size_t
343The size of said structure.
344(Initialized by driver.)
345.It Va if_data
346.Pq Vt "struct if_data"
347More statistics and information; see
348.Sx "The if_data structure" ,
349below.
350(Initialized by driver, manipulated by both driver and generic
351code.)
352.It Va if_multiaddrs
353.Pq Vt struct ifmultihead
354The head of the
355.Xr queue 3
356.Li TAILQ
357containing the list of multicast addresses assigned to this interface.
358.It Va if_amcount
359.Pq Vt int
360A number of multicast requests on this interface, used to
361reference-count the
362.Dv IFF_ALLMULTI
363flag.
364.It Va if_addr
365.Pq Vt "struct ifaddr *"
366A pointer to the link-level interface address.
367(Initialized by
368.Fn if_alloc . )
369.\" .It Va if_llsoftc
370.\" .Pq Vt "void *"
371.\" The purpose of the field is unclear.
372.It Va if_snd
373.Pq Vt "struct ifaltq"
374The output queue.
375(Manipulated by driver.)
376.It Va if_broadcastaddr
377.Pq Vt "const u_int8_t *"
378A link-level broadcast bytestring for protocols with variable address
379length.
380.It Va if_bridge
381.Pq Vt "void *"
382A pointer to the bridge interface structure,
383.Xr if_bridge 4 .
384(Initialized by the driver-specific
385.Fn if_ioctl
386routine.)
387.It Va if_label
388.Pq Vt "struct label *"
389A pointer to the MAC Framework label structure,
390.Xr mac 4 .
391(Initialized by
392.Fn if_alloc . )
393.It Va if_afdata
394.Pq Vt "void *"
395An address family dependent data region.
396.It Va if_afdata_initialized
397.Pq Vt int
398Used to track the current state of address family initialization.
399.It Va if_afdata_lock
400.Pq Vt "struct rwlock"
401An
402.Xr rwlock 9
403lock used to protect
404.Va if_afdata
405internals.
406.It Va if_linktask
407.Pq Vt "struct task"
408A
409.Xr taskqueue 9
410task scheduled for link state change events of the interface.
411.It Va if_addr_lock
412.Pq Vt "struct rwlock"
413An
414.Xr rwlock 9
415lock used to protect interface-related address lists.
416.It Va if_clones
417.Pq Fn LIST_ENTRY ifnet
418.Xr queue 3
419macro glue for the list of clonable network interfaces.
420.It Va if_groups
421.Pq Fn TAILQ_HEAD "" "ifg_list"
422The head of the
423.Xr queue 3
424.Li TAILQ
425containing the list of groups per interface.
426.It Va if_pf_kif
427.Pq Vt "void *"
428A pointer to the structure used for interface abstraction by
429.Xr pf 4 .
430.It Va if_lagg
431.Pq Vt "void *"
432A pointer to the
433.Xr lagg 4
434interface structure.
435.It Va if_alloctype
436.Pq Vt u_char
437The type of the interface as it was at the time of its allocation.
438It is used to cache the type passed to
439.Fn if_alloc ,
440but unlike
441.Va if_type ,
442it would not be changed by drivers.
443.El
444.Pp
445References to
446.Vt ifnet
447structures are gained by calling the
448.Fn if_ref
449function and released by calling the
450.Fn if_rele
451function.
452They are used to allow kernel code walking global interface lists
453to release the
454.Vt ifnet
455lock yet keep the
456.Vt ifnet
457structure stable.
458.Pp
459There are in addition a number of function pointers which the driver
460must initialize to complete its interface with the generic interface
461layer:
462.Bl -ohang -offset indent
463.It Fn if_input
464Pass a packet to an appropriate upper layer as determined
465from the link-layer header of the packet.
466This routine is to be called from an interrupt handler or
467used to emulate reception of a packet on this interface.
468A single function implementing
469.Fn if_input
470can be shared among multiple drivers utilizing the same link-layer
471framing, e.g., Ethernet.
472.It Fn if_output
473Output a packet on interface
474.Fa ifp ,
475or queue it on the output queue if the interface is already active.
476.It Fn if_transmit
477Transmit a packet on an interface or queue it if the interface is
478in use.
479This function will return
480.Dv ENOBUFS
481if the devices software and hardware queues are both full.
482This function must be installed after
483.Fn if_attach
484to override the default implementation.
485This function is exposed in order to allow drivers to manage their own queues
486and to reduce the latency caused by a frequently gratuitous enqueue / dequeue
487pair to ifq.
488The suggested internal software queueing mechanism is buf_ring.
489.It Fn if_qflush
490Free mbufs in internally managed queues when the interface is marked down.
491This function must be installed after
492.Fn if_attach
493to override the default implementation.
494This function is exposed in order to allow drivers to manage their own queues
495and to reduce the latency caused by a frequently gratuitous enqueue / dequeue
496pair to ifq.
497The suggested internal software queueing mechanism is buf_ring.
498.It Fn if_start
499Start queued output on an interface.
500This function is exposed in
501order to provide for some interface classes to share a
502.Fn if_output
503among all drivers.
504.Fn if_start
505may only be called when the
506.Dv IFF_DRV_OACTIVE
507flag is not set.
508(Thus,
509.Dv IFF_DRV_OACTIVE
510does not literally mean that output is active, but rather that the
511device's internal output queue is full.) Please note that this function
512will soon be deprecated.
513.It Fn if_ioctl
514Process interface-related
515.Xr ioctl 2
516requests
517(defined in
518.In sys/sockio.h ) .
519Preliminary processing is done by the generic routine
520.Fn ifioctl
521to check for appropriate privileges, locate the interface being
522manipulated, and perform certain generic operations like twiddling
523flags and flushing queues.
524See the description of
525.Fn ifioctl
526below for more information.
527.It Fn if_init
528Initialize and bring up the hardware,
529e.g., reset the chip and enable the receiver unit.
530Should mark the interface running,
531but not active
532.Dv ( IFF_DRV_RUNNING , ~IIF_DRV_OACTIVE ) .
533.It Fn if_resolvemulti
534Check the requested multicast group membership,
535.Fa addr ,
536for validity, and if necessary compute a link-layer group which
537corresponds to that address which is returned in
538.Fa *retsa .
539Returns zero on success, or an error code on failure.
540.El
541.Ss "Interface Flags"
542Interface flags are used for a number of different purposes.
543Some
544flags simply indicate information about the type of interface and its
545capabilities; others are dynamically manipulated to reflect the
546current state of the interface.
547Flags of the former kind are marked
548.Aq S
549in this table; the latter are marked
550.Aq D .
551Flags which begin with
552.Dq IFF_DRV_
553are stored in
554.Va if_drv_flags ;
555all other flags are stored in
556.Va if_flags .
557.Pp
558The macro
559.Dv IFF_CANTCHANGE
560defines the bits which cannot be set by a user program using the
561.Dv SIOCSIFFLAGS
562command to
563.Xr ioctl 2 ;
564these are indicated by an asterisk
565.Pq Ql *
566in the following listing.
567.Pp
568.Bl -tag -width ".Dv IFF_POINTOPOINT" -offset indent -compact
569.It Dv IFF_UP
570.Aq D
571The interface has been configured up by the user-level code.
572.It Dv IFF_BROADCAST
573.Aq S*
574The interface supports broadcast.
575.It Dv IFF_DEBUG
576.Aq D
577Used to enable/disable driver debugging code.
578.It Dv IFF_LOOPBACK
579.Aq S
580The interface is a loopback device.
581.It Dv IFF_POINTOPOINT
582.Aq S*
583The interface is point-to-point;
584.Dq broadcast
585address is actually the address of the other end.
586.It Dv IFF_DRV_RUNNING
587.Aq D*
588The interface has been configured and dynamic resources were
589successfully allocated.
590Probably only useful internal to the
591interface.
592.It Dv IFF_NOARP
593.Aq D
594Disable network address resolution on this interface.
595.It Dv IFF_PROMISC
596.Aq D*
597This interface is in promiscuous mode.
598.It Dv IFF_PPROMISC
599.Aq D
600This interface is in the permanently promiscuous mode (implies
601.Dv IFF_PROMISC ) .
602.It Dv IFF_ALLMULTI
603.Aq D*
604This interface is in all-multicasts mode (used by multicast routers).
605.It Dv IFF_DRV_OACTIVE
606.Aq D*
607The interface's hardware output queue (if any) is full; output packets
608are to be queued.
609.It Dv IFF_SIMPLEX
610.Aq S*
611The interface cannot hear its own transmissions.
612.It Dv IFF_LINK0
613.It Dv IFF_LINK1
614.It Dv IFF_LINK2
615.Aq D
616Control flags for the link layer.
617(Currently abused to select among
618multiple physical layers on some devices.)
619.It Dv IFF_MULTICAST
620.Aq S*
621This interface supports multicast.
622.It Dv IFF_CANTCONFIG
623.Aq S*
624The interface is not configurable in a meaningful way.
625Primarily useful for
626.Dv IFT_USB
627interfaces registered at the interface list.
628.It Dv IFF_MONITOR
629.Aq D
630This interface blocks transmission of packets and discards incoming
631packets after BPF processing.
632Used to monitor network traffic but not interact
633with the network in question.
634.It Dv IFF_STATICARP
635.Aq D
636Used to enable/disable ARP requests on this interface.
637.It Dv IFF_DYING
638.Aq D*
639Set when the
640.Vt ifnet
641structure of this interface is being released and still has
642.Va if_refcount
643references.
644.It Dv IFF_RENAMING
645.Aq D
646Set when this interface is being renamed.
647.El
648.Ss "Interface Capabilities Flags"
649Interface capabilities are specialized features an interface may
650or may not support.
651These capabilities are very hardware-specific
652and allow, when enabled,
653to offload specific network processing to the interface
654or to offer a particular feature for use by other kernel parts.
655.Pp
656It should be stressed that a capability can be completely
657uncontrolled (i.e., stay always enabled with no way to disable it)
658or allow limited control over itself (e.g., depend on another
659capability's state.)
660Such peculiarities are determined solely by the hardware and driver
661of a particular interface.
662Only the driver possesses
663the knowledge on whether and how the interface capabilities
664can be controlled.
665Consequently, capabilities flags in
666.Va if_capenable
667should never be modified directly by kernel code other than
668the interface driver.
669The command
670.Dv SIOCSIFCAP
671to
672.Fn ifioctl
673is the dedicated means to attempt altering
674.Va if_capenable
675on an interface.
676Userland code shall use
677.Xr ioctl 2 .
678.Pp
679The following capabilities are currently supported by the system:
680.Bl -tag -width ".Dv IFCAP_POLLING_NOCOUNT" -offset indent
681.It Dv IFCAP_RXCSUM
682This interface can do checksum validation on receiving data.
683Some interfaces do not have sufficient buffer storage to store frames
684above a certain MTU-size completely.
685The driver for the interface might disable hardware checksum validation
686if the MTU is set above the hardcoded limit.
687.It Dv IFCAP_TXCSUM
688This interface can do checksum calculation on transmitting data.
689.It Dv IFCAP_HWCSUM
690A shorthand for
691.Pq Dv IFCAP_RXCSUM | IFCAP_TXCSUM .
692.It Dv IFCAP_NETCONS
693This interface can be a network console.
694.It Dv IFCAP_VLAN_MTU
695The
696.Xr vlan 4
697driver can operate over this interface in software tagging mode
698without having to decrease MTU on
699.Xr vlan 4
700interfaces below 1500 bytes.
701This implies the ability of this interface to cope with frames somewhat
702longer than permitted by the Ethernet specification.
703.It Dv IFCAP_VLAN_HWTAGGING
704This interface can do VLAN tagging on output and
705demultiplex frames by their VLAN tag on input.
706.It Dv IFCAP_JUMBO_MTU
707This Ethernet interface can transmit and receive frames up to
7089000 bytes long.
709.It Dv IFCAP_POLLING
710This interface supports
711.Xr polling 4 .
712See below for details.
713.It Dv IFCAP_VLAN_HWCSUM
714This interface can do checksum calculation on both transmitting
715and receiving data on
716.Xr vlan 4
717interfaces (implies
718.Dv IFCAP_HWCSUM ) .
719.It Dv IFCAP_TSO4
720This Ethernet interface supports TCP4 Segmentation offloading.
721.It Dv IFCAP_TSO6
722This Ethernet interface supports TCP6 Segmentation offloading.
723.It Dv IFCAP_TSO
724A shorthand for
725.Pq Dv IFCAP_TSO4 | IFCAP_TSO6 .
726.It Dv IFCAP_TOE4
727This Ethernet interface supports TCP offloading.
728.It Dv IFCAP_TOE6
729This Ethernet interface supports TCP6 offloading.
730.It Dv IFCAP_TOE
731A shorthand for
732.Pq Dv IFCAP_TOE4 | IFCAP_TOE6 .
733.It Dv IFCAP_WOL_UCAST
734This Ethernet interface supports waking up on any Unicast packet.
735.It Dv IFCAP_WOL_MCAST
736This Ethernet interface supports waking up on any Multicast packet.
737.It Dv IFCAP_WOL_MAGIC
738This Ethernet interface supports waking up on any Magic packet such
739as those sent by
740.Xr wake 8 .
741.It Dv IFCAP_WOL
742A shorthand for
743.Pq Dv IFCAP_WOL_UCAST | IFCAP_WOL_MCAST | IFCAP_WOL_MAGIC .
744.It Dv IFCAP_TOE4
745This Ethernet interface supports TCP4 Offload Engine.
746.It Dv IFCAP_TOE6
747This Ethernet interface supports TCP6 Offload Engine.
748.It Dv IFCAP_TOE
749A shorthand for
750.Pq Dv IFCAP_TOE4 | IFCAP_TOE6 .
751.It Dv IFCAP_VLAN_HWFILTER
752This interface supports frame filtering in hardware on
753.Xr vlan 4
754interfaces.
755.It Dv IFCAP_POLLING_NOCOUNT
756The return value for the number of processed packets should be
757skipped for this interface.
758.It Dv IFCAP_VLAN_HWTSO
759This interface supports TCP Segmentation offloading on
760.Xr vlan 4
761interfaces (implies
762.Dv IFCAP_TSO ) .
763.It Dv IFCAP_LINKSTATE
764This Ethernet interface supports dynamic link state changes.
765.El
766.Pp
767The ability of advanced network interfaces to offload certain
768computational tasks from the host CPU to the board is limited
769mostly to TCP/IP.
770Therefore a separate field associated with an interface
771(see
772.Va ifnet.if_data.ifi_hwassist
773below)
774keeps a detailed description of its enabled capabilities
775specific to TCP/IP processing.
776The TCP/IP module consults the field to see which tasks
777can be done on an
778.Em outgoing
779packet by the interface.
780The flags defined for that field are a superset of those for
781.Va mbuf.m_pkthdr.csum_flags ,
782namely:
783.Bl -tag -width ".Dv CSUM_FRAGMENT" -offset indent
784.It Dv CSUM_IP
785The interface will compute IP checksums.
786.It Dv CSUM_TCP
787The interface will compute TCP checksums.
788.It Dv CSUM_UDP
789The interface will compute UDP checksums.
790.El
791.Pp
792An interface notifies the TCP/IP module about the tasks
793the former has performed on an
794.Em incoming
795packet by setting the corresponding flags in the field
796.Va mbuf.m_pkthdr.csum_flags
797of the
798.Vt mbuf chain
799containing the packet.
800See
801.Xr mbuf 9
802for details.
803.Pp
804The capability of a network interface to operate in
805.Xr polling 4
806mode involves several flags in different
807global variables and per-interface fields.
808The capability flag
809.Dv IFCAP_POLLING
810set in interface's
811.Va if_capabilities
812indicates support for
813.Xr polling 4
814on the particular interface.
815If set in
816.Va if_capabilities ,
817the same flag can be marked or cleared in the interface's
818.Va if_capenable
819within
820.Fn ifioctl ,
821thus initiating switch of the interface to
822.Xr polling 4
823mode or interrupt
824mode, respectively.
825The actual mode change is managed by the driver-specific
826.Fn if_ioctl
827routine.
828The
829.Xr polling
830handler returns the number of packets processed.
831.Ss The if_data Structure
832The
833.Vt if_data
834structure contains statistics and identifying information used
835by management programs, and which is exported to user programs by way
836of the
837.Xr ifmib 4
838branch of the
839.Xr sysctl 3
840MIB.
841The following elements of the
842.Vt if_data
843structure are initialized by the interface and are not expected to change
844significantly over the course of normal operation:
845.Bl -tag -width ".Va ifi_lastchange" -offset indent
846.It Va ifi_type
847.Pq Vt u_char
848The type of the interface, as defined in
849.In net/if_types.h
850and described below in the
851.Sx "Interface Types"
852section.
853.It Va ifi_physical
854.Pq Vt u_char
855Intended to represent a selection of physical layers on devices which
856support more than one; never implemented.
857.It Va ifi_addrlen
858.Pq Vt u_char
859Length of a link-layer address on this device, or zero if there are
860none.
861Used to initialized the address length field in
862.Vt sockaddr_dl
863structures referring to this interface.
864.It Va ifi_hdrlen
865.Pq Vt u_char
866Maximum length of any link-layer header which might be prepended by
867the driver to a packet before transmission.
868The generic code computes
869the maximum over all interfaces and uses that value to influence the
870placement of data in
871.Vt mbuf Ns s
872to attempt to ensure that there is always
873sufficient space to prepend a link-layer header without allocating an
874additional
875.Vt mbuf .
876.It Va ifi_datalen
877.Pq Vt u_char
878Length of the
879.Vt if_data
880structure.
881Allows some stabilization of the routing socket ABI in the face of
882increases in the length of
883.Vt struct ifdata .
884.It Va ifi_mtu
885.Pq Vt u_long
886The maximum transmission unit of the medium, exclusive of any
887link-layer overhead.
888.It Va ifi_metric
889.Pq Vt u_long
890A dimensionless metric interpreted by a user-mode routing process.
891.It Va ifi_baudrate
892.Pq Vt u_long
893The line rate of the interface, in bits per second.
894.It Va ifi_hwassist
895.Pq Vt u_long
896A detailed interpretation of the capabilities
897to offload computational tasks for
898.Em outgoing
899packets.
900The interface driver must keep this field in accord with
901the current value of
902.Va if_capenable .
903.It Va ifi_epoch
904.Pq Vt time_t
905The system uptime when interface was attached or the statistics
906below were reset.
907This is intended to be used to set the SNMP variable
908.Va ifCounterDiscontinuityTime .
909It may also be used to determine if two successive queries for an
910interface of the same index have returned results for the same
911interface.
912.El
913.Pp
914The structure additionally contains generic statistics applicable to a
915variety of different interface types (except as noted, all members are
916of type
917.Vt u_long ) :
918.Bl -tag -width ".Va ifi_lastchange" -offset indent
919.It Va ifi_link_state
920.Pq Vt u_char
921The current link state of Ethernet interfaces.
922See the
923.Sx Interface Link States
924section for possible values.
925.It Va ifi_ipackets
926Number of packets received.
927.It Va ifi_ierrors
928Number of receive errors detected (e.g., FCS errors, DMA overruns,
929etc.).
930More detailed breakdowns can often be had by way of a
931link-specific MIB.
932.It Va ifi_opackets
933Number of packets transmitted.
934.It Va ifi_oerrors
935Number of output errors detected (e.g., late collisions, DMA overruns,
936etc.).
937More detailed breakdowns can often be had by way of a
938link-specific MIB.
939.It Va ifi_collisions
940Total number of collisions detected on output for CSMA interfaces.
941(This member is sometimes [ab]used by other types of interfaces for
942other output error counts.)
943.It Va ifi_ibytes
944Total traffic received, in bytes.
945.It Va ifi_obytes
946Total traffic transmitted, in bytes.
947.It Va ifi_imcasts
948Number of packets received which were sent by link-layer multicast.
949.It Va ifi_omcasts
950Number of packets sent by link-layer multicast.
951.It Va ifi_iqdrops
952Number of packets dropped on input.
953Rarely implemented.
954.It Va ifi_noproto
955Number of packets received for unknown network-layer protocol.
956.It Va ifi_lastchange
957.Pq Vt "struct timeval"
958The time of the last administrative change to the interface (as required
959for
960.Tn SNMP ) .
961.El
962.Ss Interface Types
963The header file
964.In net/if_types.h
965defines symbolic constants for a number of different types of
966interfaces.
967The most common are:
968.Pp
969.Bl -tag -offset indent -width ".Dv IFT_PROPVIRTUAL" -compact
970.It Dv IFT_OTHER
971none of the following
972.It Dv IFT_ETHER
973Ethernet
974.It Dv IFT_ISO88023
975ISO 8802-3 CSMA/CD
976.It Dv IFT_ISO88024
977ISO 8802-4 Token Bus
978.It Dv IFT_ISO88025
979ISO 8802-5 Token Ring
980.It Dv IFT_ISO88026
981ISO 8802-6 DQDB MAN
982.It Dv IFT_FDDI
983FDDI
984.It Dv IFT_PPP
985Internet Point-to-Point Protocol
986.Pq Xr ppp 8
987.It Dv IFT_LOOP
988The loopback
989.Pq Xr lo 4
990interface
991.It Dv IFT_SLIP
992Serial Line IP
993.It Dv IFT_PARA
994Parallel-port IP
995.Pq Dq Tn PLIP
996.It Dv IFT_ATM
997Asynchronous Transfer Mode
998.It Dv IFT_USB
999USB Interface
1000.El
1001.Ss Interface Link States
1002The following link states are currently defined:
1003.Pp
1004.Bl -tag -offset indent -width ".Dv LINK_STATE_UNKNOWN" -compact
1005.It Dv LINK_STATE_UNKNOWN
1006The link is in an invalid or unknown state.
1007.It Dv LINK_STATE_DOWN
1008The link is down.
1009.It Dv LINK_STATE_UP
1010The link is up.
1011.El
1012.Ss The ifaddr Structure
1013Every interface is associated with a list
1014(or, rather, a
1015.Li TAILQ )
1016of addresses, rooted at the interface structure's
1017.Va if_addrhead
1018member.
1019The first element in this list is always an
1020.Dv AF_LINK
1021address representing the interface itself; multi-access network
1022drivers should complete this structure by filling in their link-layer
1023addresses after calling
1024.Fn if_attach .
1025Other members of the structure represent network-layer addresses which
1026have been configured by means of the
1027.Dv SIOCAIFADDR
1028command to
1029.Xr ioctl 2 ,
1030called on a socket of the appropriate protocol family.
1031The elements of this list consist of
1032.Vt ifaddr
1033structures.
1034Most protocols will declare their own protocol-specific
1035interface address structures, but all begin with a
1036.Vt "struct ifaddr"
1037which provides the most-commonly-needed functionality across all
1038protocols.
1039Interface addresses are reference-counted.
1040.Pp
1041The members of
1042.Vt "struct ifaddr"
1043are as follows:
1044.Bl -tag -width ".Va ifa_rtrequest" -offset indent
1045.It Va ifa_addr
1046.Pq Vt "struct sockaddr *"
1047The local address of the interface.
1048.It Va ifa_dstaddr
1049.Pq Vt "struct sockaddr *"
1050The remote address of point-to-point interfaces, and the broadcast
1051address of broadcast interfaces.
1052.Va ( ifa_broadaddr
1053is a macro for
1054.Va ifa_dstaddr . )
1055.It Va ifa_netmask
1056.Pq Vt "struct sockaddr *"
1057The network mask for multi-access interfaces, and the confusion
1058generator for point-to-point interfaces.
1059.It Va ifa_ifp
1060.Pq Vt "struct ifnet *"
1061A link back to the interface structure.
1062.It Va ifa_link
1063.Pq Fn TAILQ_ENTRY ifaddr
1064.Xr queue 3
1065glue for list of addresses on each interface.
1066.It Va ifa_rtrequest
1067See below.
1068.It Va ifa_flags
1069.Pq Vt u_short
1070Some of the flags which would be used for a route representing this
1071address in the route table.
1072.It Va ifa_refcnt
1073.Pq Vt short
1074The reference count.
1075.El
1076.Pp
1077References to
1078.Vt ifaddr
1079structures are gained by calling the
1080.Fn ifa_ref
1081function and released by calling the
1082.Fn ifa_free
1083function.
1084.Pp
1085.Fn ifa_rtrequest
1086is a pointer to a function which receives callouts from the routing
1087code
1088.Pq Fn rtrequest
1089to perform link-layer-specific actions upon requests to add,
1090or delete routes.
1091The
1092.Fa cmd
1093argument indicates the request in question:
1094.Dv RTM_ADD ,
1095or
1096.Dv RTM_DELETE .
1097The
1098.Fa rt
1099argument is the route in question; the
1100.Fa info
1101argument contains the specific destination being manipulated.
1102.Sh FUNCTIONS
1103The functions provided by the generic interface code can be divided
1104into two groups: those which manipulate interfaces, and those which
1105manipulate interface addresses.
1106In addition to these functions, there
1107may also be link-layer support routines which are used by a number of
1108drivers implementing a specific link layer over different hardware;
1109see the documentation for that link layer for more details.
1110.Ss The ifmultiaddr Structure
1111Every multicast-capable interface is associated with a list of
1112multicast group memberships, which indicate at a low level which
1113link-layer multicast addresses (if any) should be accepted, and at a
1114high level, in which network-layer multicast groups a user process has
1115expressed interest.
1116.Pp
1117The elements of the structure are as follows:
1118.Bl -tag -width ".Va ifma_refcount" -offset indent
1119.It Va ifma_link
1120.Pq Fn LIST_ENTRY ifmultiaddr
1121.Xr queue 3
1122macro glue.
1123.It Va ifma_addr
1124.Pq Vt "struct sockaddr *"
1125A pointer to the address which this record represents.
1126The
1127memberships for various address families are stored in arbitrary
1128order.
1129.It Va ifma_lladdr
1130.Pq Vt "struct sockaddr *"
1131A pointer to the link-layer multicast address, if any, to which the
1132network-layer multicast address in
1133.Va ifma_addr
1134is mapped, else a null pointer.
1135If this element is non-nil, this
1136membership also holds an invisible reference to another membership for
1137that link-layer address.
1138.It Va ifma_refcount
1139.Pq Vt u_int
1140A reference count of requests for this particular membership.
1141.El
1142.Ss Interface Manipulation Functions
1143.Bl -ohang -offset indent
1144.It Fn if_alloc
1145Allocate and initialize
1146.Vt "struct ifnet" .
1147Initialization includes the allocation of an interface index and may
1148include the allocation of a
1149.Fa type
1150specific structure in
1151.Va if_l2com .
1152.It Fn if_attach
1153Link the specified interface
1154.Fa ifp
1155into the list of network interfaces.
1156Also initialize the list of
1157addresses on that interface, and create a link-layer
1158.Vt ifaddr
1159structure to be the first element in that list.
1160(A pointer to
1161this address structure is saved in the
1162.Vt ifnet
1163structure and is accessed by the
1164.Fn ifaddr_byindex
1165function.)
1166The
1167.Fa ifp
1168must have been allocated by
1169.Fn if_alloc .
1170.It Fn if_detach
1171Shut down and unlink the specified
1172.Fa ifp
1173from the interface list.
1174.It Fn if_free
1175Free the given
1176.Fa ifp
1177back to the system.
1178The interface must have been previously detached if it was ever attached.
1179.It Fn if_free_type
1180Identical to
1181.Fn if_free
1182except that the given
1183.Fa type
1184is used to free
1185.Va if_l2com
1186instead of the type in
1187.Va if_type .
1188This is intended for use with drivers that change their interface type.
1189.It Fn if_down
1190Mark the interface
1191.Fa ifp
1192as down (i.e.,
1193.Dv IFF_UP
1194is not set),
1195flush its output queue, notify protocols of the transition,
1196and generate a message from the
1197.Xr route 4
1198routing socket.
1199.It Fn if_up
1200Mark the interface
1201.Fa ifp
1202as up, notify protocols of the transition,
1203and generate a message from the
1204.Xr route 4
1205routing socket.
1206.It Fn ifpromisc
1207Add or remove a promiscuous reference to
1208.Fa ifp .
1209If
1210.Fa pswitch
1211is true, add a reference;
1212if it is false, remove a reference.
1213On reference count transitions
1214from zero to one and one to zero, set the
1215.Dv IFF_PROMISC
1216flag appropriately and call
1217.Fn if_ioctl
1218to set up the interface in the desired mode.
1219.It Fn if_allmulti
1220As
1221.Fn ifpromisc ,
1222but for the all-multicasts
1223.Pq Dv IFF_ALLMULTI
1224flag instead of the promiscuous flag.
1225.It Fn ifunit
1226Return an
1227.Vt ifnet
1228pointer for the interface named
1229.Fa name .
1230.It Fn ifunit_ref
1231Return a reference-counted (via
1232.Fn ifa_ref )
1233.Vt ifnet
1234pointer for the interface named
1235.Fa name .
1236This is the preferred function over
1237.Fn ifunit .
1238The caller is responsible for releasing the reference with
1239.Fn if_rele
1240when it is finished with the ifnet.
1241.It Fn ifioctl
1242Process the ioctl request
1243.Fa cmd ,
1244issued on socket
1245.Fa so
1246by thread
1247.Fa td ,
1248with data parameter
1249.Fa data .
1250This is the main routine for handling all interface configuration
1251requests from user mode.
1252It is ordinarily only called from the socket-layer
1253.Xr ioctl 2
1254handler, and only for commands with class
1255.Sq Li i .
1256Any unrecognized commands will be passed down to socket
1257.Fa so Ns 's
1258protocol for
1259further interpretation.
1260The following commands are handled by
1261.Fn ifioctl :
1262.Pp
1263.Bl -tag -width ".Dv SIOCGIFNETMASK" -offset indent -compact
1264.It Dv SIOCGIFCONF
1265Get interface configuration.
1266(No call-down to driver.)
1267.Pp
1268.It Dv SIOCSIFNAME
1269Set the interface name.
1270.Dv RTM_IFANNOUNCE
1271departure and arrival messages are sent so that
1272routing code that relies on the interface name will update its interface
1273list.
1274Caller must have appropriate privilege.
1275(No call-down to driver.)
1276.It Dv SIOCGIFCAP
1277.It Dv SIOCGIFFIB
1278.It Dv SIOCGIFFLAGS
1279.It Dv SIOCGIFMETRIC
1280.It Dv SIOCGIFMTU
1281.It Dv SIOCGIFPHYS
1282Get interface capabilities, FIB, flags, metric, MTU, medium selection.
1283(No call-down to driver.)
1284.Pp
1285.It Dv SIOCSIFCAP
1286Enable or disable interface capabilities.
1287Caller must have appropriate privilege.
1288Before a call to the driver-specific
1289.Fn if_ioctl
1290routine, the requested mask for enabled capabilities is checked
1291against the mask of capabilities supported by the interface,
1292.Va if_capabilities .
1293Requesting to enable an unsupported capability is invalid.
1294The rest is supposed to be done by the driver,
1295which includes updating
1296.Va if_capenable
1297and
1298.Va if_data.ifi_hwassist
1299appropriately.
1300.Pp
1301.It Dv SIOCSIFFIB
1302Sets interface FIB.
1303Caller must have appropriate privilege.
1304FIB values start at 0 and values greater or equals than
1305.Va net.fibs
1306are considered invalid.
1307.It Dv SIOCSIFFLAGS
1308Change interface flags.
1309Caller must have appropriate privilege.
1310If a change to the
1311.Dv IFF_UP
1312flag is requested,
1313.Fn if_up
1314or
1315.Fn if_down
1316is called as appropriate.
1317Flags listed in
1318.Dv IFF_CANTCHANGE
1319are masked off, and the field
1320.Va if_flags
1321in the interface structure is updated.
1322Finally, the driver
1323.Fn if_ioctl
1324routine is called to perform any setup
1325requested.
1326.Pp
1327.It Dv SIOCSIFMETRIC
1328.It Dv SIOCSIFPHYS
1329Change interface metric or medium.
1330Caller must have appropriate privilege.
1331.Pp
1332.It Dv SIOCSIFMTU
1333Change interface MTU.
1334Caller must have appropriate privilege.
1335MTU
1336values less than 72 or greater than 65535 are considered invalid.
1337The driver
1338.Fn if_ioctl
1339routine is called to implement the change; it is responsible for any
1340additional sanity checking and for actually modifying the MTU in the
1341interface structure.
1342.Pp
1343.It Dv SIOCADDMULTI
1344.It Dv SIOCDELMULTI
1345Add or delete permanent multicast group memberships on the interface.
1346Caller must have appropriate privilege.
1347The
1348.Fn if_addmulti
1349or
1350.Fn if_delmulti
1351function is called to perform the operation; qq.v.
1352.Pp
1353.It Dv SIOCAIFADDR
1354.It Dv SIOCDIFADDR
1355The socket's protocol control routine is called to implement the
1356requested action.
1357.El
1358.El
1359.Pp
1360.Fn if_down ,
1361.Fn ifioctl ,
1362.Fn ifpromisc ,
1363and
1364.Fn if_up
1365must be called at
1366.Fn splnet
1367or higher.
1368.Ss "Interface Address Functions"
1369Several functions exist to look up an interface address structure
1370given an address.
1371.Fn ifa_ifwithaddr
1372returns an interface address with either a local address or a
1373broadcast address precisely matching the parameter
1374.Fa addr .
1375.Fn ifa_ifwithdstaddr
1376returns an interface address for a point-to-point interface whose
1377remote
1378.Pq Dq destination
1379address is
1380.Fa addr
1381and a fib is
1382.Fa fib .
1383If
1384.Fa fib
1385is
1386.Dv RT_ALL_FIBS ,
1387then the first interface address matching
1388.Fa addr
1389will be returned.
1390.Pp
1391.Fn ifa_ifwithnet
1392returns the most specific interface address which matches the
1393specified address,
1394.Fa addr ,
1395subject to its configured netmask, or a point-to-point interface
1396address whose remote address is
1397.Fa addr
1398if one is found.
1399If
1400.Fa ignore_ptp
1401is true, skip point-to-point interface addresses.
1402The
1403.Fa fib
1404parameter is handled the same way as by
1405.Fn ifa_ifwithdstaddr .
1406.Pp
1407.Fn ifaof_ifpforaddr
1408returns the most specific address configured on interface
1409.Fa ifp
1410which matches address
1411.Fa addr ,
1412subject to its configured netmask.
1413If the interface is
1414point-to-point, only an interface address whose remote address is
1415precisely
1416.Fa addr
1417will be returned.
1418.Pp
1419.Fn ifaddr_byindex
1420returns the link-level address of the interface with the given index
1421.Fa idx .
1422.Pp
1423All of these functions return a null pointer if no such address can be
1424found.
1425.Ss "Interface Multicast Address Functions"
1426The
1427.Fn if_addmulti ,
1428.Fn if_delmulti ,
1429and
1430.Fn if_findmulti
1431functions provide support for requesting and relinquishing multicast
1432group memberships, and for querying an interface's membership list,
1433respectively.
1434The
1435.Fn if_addmulti
1436function takes a pointer to an interface,
1437.Fa ifp ,
1438and a generic address,
1439.Fa sa .
1440It also takes a pointer to a
1441.Vt "struct ifmultiaddr *"
1442which is filled in on successful return with the address of the
1443group membership control block.
1444The
1445.Fn if_addmulti
1446function performs the following four-step process:
1447.Bl -enum -offset indent
1448.It
1449Call the interface's
1450.Fn if_resolvemulti
1451entry point to determine the link-layer address, if any, corresponding
1452to this membership request, and also to give the link layer an
1453opportunity to veto this membership request should it so desire.
1454.It
1455Check the interface's group membership list for a pre-existing
1456membership for this group.
1457If one is not found, allocate a new one;
1458if one is, increment its reference count.
1459.It
1460If the
1461.Fn if_resolvemulti
1462routine returned a link-layer address corresponding to the group,
1463repeat the previous step for that address as well.
1464.It
1465If the interface's multicast address filter needs to be changed
1466because a new membership was added, call the interface's
1467.Fn if_ioctl
1468routine
1469(with a
1470.Fa cmd
1471argument of
1472.Dv SIOCADDMULTI )
1473to request that it do so.
1474.El
1475.Pp
1476The
1477.Fn if_delmulti
1478function, given an interface
1479.Fa ifp
1480and an address,
1481.Fa sa ,
1482reverses this process.
1483Both functions return zero on success, or a
1484standard error number on failure.
1485.Pp
1486The
1487.Fn if_findmulti
1488function examines the membership list of interface
1489.Fa ifp
1490for an address matching
1491.Fa sa ,
1492and returns a pointer to that
1493.Vt "struct ifmultiaddr"
1494if one is found, else it returns a null pointer.
1495.Sh SEE ALSO
1496.Xr ioctl 2 ,
1497.Xr link_addr 3 ,
1498.Xr queue 3 ,
1499.Xr sysctl 3 ,
1500.Xr bpf 4 ,
1501.Xr ifmib 4 ,
1502.Xr lo 4 ,
1503.Xr netintro 4 ,
1504.Xr polling 4 ,
1505.Xr config 8 ,
1506.Xr ppp 8 ,
1507.Xr mbuf 9 ,
1508.Xr rtentry 9
1509.Rs
1510.%A Gary R. Wright
1511.%A W. Richard Stevens
1512.%B TCP/IP Illustrated
1513.%V Vol. 2
1514.%O Addison-Wesley, ISBN 0-201-63354-X
1515.Re
1516.Sh AUTHORS
1517This manual page was written by
1518.An Garrett A. Wollman .
1519