xref: /freebsd/share/man/man9/ifnet.9 (revision c6db8143eda5c775467145ac73e8ebec47afdd8f)
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31.Dd July 29, 2014
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 Vt ifnet Ss 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.It Dv CSUM_IP_FRAGS
791The interface can compute a TCP or UDP checksum for a packet
792fragmented by the host CPU.
793Makes sense only along with
794.Dv CSUM_TCP
795or
796.Dv CSUM_UDP .
797.It Dv CSUM_FRAGMENT
798The interface will do the fragmentation of IP packets if necessary.
799The host CPU does not need to care about MTU on this interface
800as long as a packet to transmit through it is an IP one and it
801does not exceed the size of the hardware buffer.
802.El
803.Pp
804An interface notifies the TCP/IP module about the tasks
805the former has performed on an
806.Em incoming
807packet by setting the corresponding flags in the field
808.Va mbuf.m_pkthdr.csum_flags
809of the
810.Vt mbuf chain
811containing the packet.
812See
813.Xr mbuf 9
814for details.
815.Pp
816The capability of a network interface to operate in
817.Xr polling 4
818mode involves several flags in different
819global variables and per-interface fields.
820The capability flag
821.Dv IFCAP_POLLING
822set in interface's
823.Va if_capabilities
824indicates support for
825.Xr polling 4
826on the particular interface.
827If set in
828.Va if_capabilities ,
829the same flag can be marked or cleared in the interface's
830.Va if_capenable
831within
832.Fn ifioctl ,
833thus initiating switch of the interface to
834.Xr polling 4
835mode or interrupt
836mode, respectively.
837The actual mode change is managed by the driver-specific
838.Fn if_ioctl
839routine.
840The
841.Xr polling
842handler returns the number of packets processed.
843.Ss The Vt if_data Ss Structure
844The
845.Vt if_data
846structure contains statistics and identifying information used
847by management programs, and which is exported to user programs by way
848of the
849.Xr ifmib 4
850branch of the
851.Xr sysctl 3
852MIB.
853The following elements of the
854.Vt if_data
855structure are initialized by the interface and are not expected to change
856significantly over the course of normal operation:
857.Bl -tag -width ".Va ifi_lastchange" -offset indent
858.It Va ifi_type
859.Pq Vt u_char
860The type of the interface, as defined in
861.In net/if_types.h
862and described below in the
863.Sx "Interface Types"
864section.
865.It Va ifi_physical
866.Pq Vt u_char
867Intended to represent a selection of physical layers on devices which
868support more than one; never implemented.
869.It Va ifi_addrlen
870.Pq Vt u_char
871Length of a link-layer address on this device, or zero if there are
872none.
873Used to initialized the address length field in
874.Vt sockaddr_dl
875structures referring to this interface.
876.It Va ifi_hdrlen
877.Pq Vt u_char
878Maximum length of any link-layer header which might be prepended by
879the driver to a packet before transmission.
880The generic code computes
881the maximum over all interfaces and uses that value to influence the
882placement of data in
883.Vt mbuf Ns s
884to attempt to ensure that there is always
885sufficient space to prepend a link-layer header without allocating an
886additional
887.Vt mbuf .
888.It Va ifi_datalen
889.Pq Vt u_char
890Length of the
891.Vt if_data
892structure.
893Allows some stabilization of the routing socket ABI in the face of
894increases in the length of
895.Vt struct ifdata .
896.It Va ifi_mtu
897.Pq Vt u_long
898The maximum transmission unit of the medium, exclusive of any
899link-layer overhead.
900.It Va ifi_metric
901.Pq Vt u_long
902A dimensionless metric interpreted by a user-mode routing process.
903.It Va ifi_baudrate
904.Pq Vt u_long
905The line rate of the interface, in bits per second.
906.It Va ifi_hwassist
907.Pq Vt u_long
908A detailed interpretation of the capabilities
909to offload computational tasks for
910.Em outgoing
911packets.
912The interface driver must keep this field in accord with
913the current value of
914.Va if_capenable .
915.It Va ifi_epoch
916.Pq Vt time_t
917The system uptime when interface was attached or the statistics
918below were reset.
919This is intended to be used to set the SNMP variable
920.Va ifCounterDiscontinuityTime .
921It may also be used to determine if two successive queries for an
922interface of the same index have returned results for the same
923interface.
924.El
925.Pp
926The structure additionally contains generic statistics applicable to a
927variety of different interface types (except as noted, all members are
928of type
929.Vt u_long ) :
930.Bl -tag -width ".Va ifi_lastchange" -offset indent
931.It Va ifi_link_state
932.Pq Vt u_char
933The current link state of Ethernet interfaces.
934See the
935.Sx Interface Link States
936section for possible values.
937.It Va ifi_ipackets
938Number of packets received.
939.It Va ifi_ierrors
940Number of receive errors detected (e.g., FCS errors, DMA overruns,
941etc.).
942More detailed breakdowns can often be had by way of a
943link-specific MIB.
944.It Va ifi_opackets
945Number of packets transmitted.
946.It Va ifi_oerrors
947Number of output errors detected (e.g., late collisions, DMA overruns,
948etc.).
949More detailed breakdowns can often be had by way of a
950link-specific MIB.
951.It Va ifi_collisions
952Total number of collisions detected on output for CSMA interfaces.
953(This member is sometimes [ab]used by other types of interfaces for
954other output error counts.)
955.It Va ifi_ibytes
956Total traffic received, in bytes.
957.It Va ifi_obytes
958Total traffic transmitted, in bytes.
959.It Va ifi_imcasts
960Number of packets received which were sent by link-layer multicast.
961.It Va ifi_omcasts
962Number of packets sent by link-layer multicast.
963.It Va ifi_iqdrops
964Number of packets dropped on input.
965Rarely implemented.
966.It Va ifi_noproto
967Number of packets received for unknown network-layer protocol.
968.It Va ifi_lastchange
969.Pq Vt "struct timeval"
970The time of the last administrative change to the interface (as required
971for
972.Tn SNMP ) .
973.El
974.Ss Interface Types
975The header file
976.In net/if_types.h
977defines symbolic constants for a number of different types of
978interfaces.
979The most common are:
980.Pp
981.Bl -tag -offset indent -width ".Dv IFT_PROPVIRTUAL" -compact
982.It Dv IFT_OTHER
983none of the following
984.It Dv IFT_ETHER
985Ethernet
986.It Dv IFT_ISO88023
987ISO 8802-3 CSMA/CD
988.It Dv IFT_ISO88024
989ISO 8802-4 Token Bus
990.It Dv IFT_ISO88025
991ISO 8802-5 Token Ring
992.It Dv IFT_ISO88026
993ISO 8802-6 DQDB MAN
994.It Dv IFT_FDDI
995FDDI
996.It Dv IFT_PPP
997Internet Point-to-Point Protocol
998.Pq Xr ppp 8
999.It Dv IFT_LOOP
1000The loopback
1001.Pq Xr lo 4
1002interface
1003.It Dv IFT_SLIP
1004Serial Line IP
1005.It Dv IFT_PARA
1006Parallel-port IP
1007.Pq Dq Tn PLIP
1008.It Dv IFT_ATM
1009Asynchronous Transfer Mode
1010.It Dv IFT_USB
1011USB Interface
1012.El
1013.Ss Interface Link States
1014The following link states are currently defined:
1015.Pp
1016.Bl -tag -offset indent -width ".Dv LINK_STATE_UNKNOWN" -compact
1017.It Dv LINK_STATE_UNKNOWN
1018The link is in an invalid or unknown state.
1019.It Dv LINK_STATE_DOWN
1020The link is down.
1021.It Dv LINK_STATE_UP
1022The link is up.
1023.El
1024.Ss The Vt ifaddr Ss Structure
1025Every interface is associated with a list
1026(or, rather, a
1027.Li TAILQ )
1028of addresses, rooted at the interface structure's
1029.Va if_addrlist
1030member.
1031The first element in this list is always an
1032.Dv AF_LINK
1033address representing the interface itself; multi-access network
1034drivers should complete this structure by filling in their link-layer
1035addresses after calling
1036.Fn if_attach .
1037Other members of the structure represent network-layer addresses which
1038have been configured by means of the
1039.Dv SIOCAIFADDR
1040command to
1041.Xr ioctl 2 ,
1042called on a socket of the appropriate protocol family.
1043The elements of this list consist of
1044.Vt ifaddr
1045structures.
1046Most protocols will declare their own protocol-specific
1047interface address structures, but all begin with a
1048.Vt "struct ifaddr"
1049which provides the most-commonly-needed functionality across all
1050protocols.
1051Interface addresses are reference-counted.
1052.Pp
1053The members of
1054.Vt "struct ifaddr"
1055are as follows:
1056.Bl -tag -width ".Va ifa_rtrequest" -offset indent
1057.It Va ifa_addr
1058.Pq Vt "struct sockaddr *"
1059The local address of the interface.
1060.It Va ifa_dstaddr
1061.Pq Vt "struct sockaddr *"
1062The remote address of point-to-point interfaces, and the broadcast
1063address of broadcast interfaces.
1064.Va ( ifa_broadaddr
1065is a macro for
1066.Va ifa_dstaddr . )
1067.It Va ifa_netmask
1068.Pq Vt "struct sockaddr *"
1069The network mask for multi-access interfaces, and the confusion
1070generator for point-to-point interfaces.
1071.It Va ifa_ifp
1072.Pq Vt "struct ifnet *"
1073A link back to the interface structure.
1074.It Va ifa_link
1075.Pq Fn TAILQ_ENTRY ifaddr
1076.Xr queue 3
1077glue for list of addresses on each interface.
1078.It Va ifa_rtrequest
1079See below.
1080.It Va ifa_flags
1081.Pq Vt u_short
1082Some of the flags which would be used for a route representing this
1083address in the route table.
1084.It Va ifa_refcnt
1085.Pq Vt short
1086The reference count.
1087.El
1088.Pp
1089References to
1090.Vt ifaddr
1091structures are gained by calling the
1092.Fn ifa_ref
1093function and released by calling the
1094.Fn ifa_free
1095function.
1096.Pp
1097.Fn ifa_rtrequest
1098is a pointer to a function which receives callouts from the routing
1099code
1100.Pq Fn rtrequest
1101to perform link-layer-specific actions upon requests to add,
1102or delete routes.
1103The
1104.Fa cmd
1105argument indicates the request in question:
1106.Dv RTM_ADD ,
1107or
1108.Dv RTM_DELETE .
1109The
1110.Fa rt
1111argument is the route in question; the
1112.Fa info
1113argument contains the specific destination being manipulated.
1114.Sh FUNCTIONS
1115The functions provided by the generic interface code can be divided
1116into two groups: those which manipulate interfaces, and those which
1117manipulate interface addresses.
1118In addition to these functions, there
1119may also be link-layer support routines which are used by a number of
1120drivers implementing a specific link layer over different hardware;
1121see the documentation for that link layer for more details.
1122.Ss The Vt ifmultiaddr Ss Structure
1123Every multicast-capable interface is associated with a list of
1124multicast group memberships, which indicate at a low level which
1125link-layer multicast addresses (if any) should be accepted, and at a
1126high level, in which network-layer multicast groups a user process has
1127expressed interest.
1128.Pp
1129The elements of the structure are as follows:
1130.Bl -tag -width ".Va ifma_refcount" -offset indent
1131.It Va ifma_link
1132.Pq Fn LIST_ENTRY ifmultiaddr
1133.Xr queue 3
1134macro glue.
1135.It Va ifma_addr
1136.Pq Vt "struct sockaddr *"
1137A pointer to the address which this record represents.
1138The
1139memberships for various address families are stored in arbitrary
1140order.
1141.It Va ifma_lladdr
1142.Pq Vt "struct sockaddr *"
1143A pointer to the link-layer multicast address, if any, to which the
1144network-layer multicast address in
1145.Va ifma_addr
1146is mapped, else a null pointer.
1147If this element is non-nil, this
1148membership also holds an invisible reference to another membership for
1149that link-layer address.
1150.It Va ifma_refcount
1151.Pq Vt u_int
1152A reference count of requests for this particular membership.
1153.El
1154.Ss Interface Manipulation Functions
1155.Bl -ohang -offset indent
1156.It Fn if_alloc
1157Allocate and initialize
1158.Vt "struct ifnet" .
1159Initialization includes the allocation of an interface index and may
1160include the allocation of a
1161.Fa type
1162specific structure in
1163.Va if_l2com .
1164.It Fn if_attach
1165Link the specified interface
1166.Fa ifp
1167into the list of network interfaces.
1168Also initialize the list of
1169addresses on that interface, and create a link-layer
1170.Vt ifaddr
1171structure to be the first element in that list.
1172(A pointer to
1173this address structure is saved in the
1174.Vt ifnet
1175structure and shall be accessed by the
1176.Fn ifaddr_byindex
1177function.)
1178The
1179.Fa ifp
1180must have been allocated by
1181.Fn if_alloc .
1182.It Fn if_detach
1183Shut down and unlink the specified
1184.Fa ifp
1185from the interface list.
1186.It Fn if_free
1187Free the given
1188.Fa ifp
1189back to the system.
1190The interface must have been previously detached if it was ever attached.
1191.It Fn if_free_type
1192Identical to
1193.Fn if_free
1194except that the given
1195.Fa type
1196is used to free
1197.Va if_l2com
1198instead of the type in
1199.Va if_type .
1200This is intended for use with drivers that change their interface type.
1201.It Fn if_down
1202Mark the interface
1203.Fa ifp
1204as down (i.e.,
1205.Dv IFF_UP
1206is not set),
1207flush its output queue, notify protocols of the transition,
1208and generate a message from the
1209.Xr route 4
1210routing socket.
1211.It Fn if_up
1212Mark the interface
1213.Fa ifp
1214as up, notify protocols of the transition,
1215and generate a message from the
1216.Xr route 4
1217routing socket.
1218.It Fn ifpromisc
1219Add or remove a promiscuous reference to
1220.Fa ifp .
1221If
1222.Fa pswitch
1223is true, add a reference;
1224if it is false, remove a reference.
1225On reference count transitions
1226from zero to one and one to zero, set the
1227.Dv IFF_PROMISC
1228flag appropriately and call
1229.Fn if_ioctl
1230to set up the interface in the desired mode.
1231.It Fn if_allmulti
1232As
1233.Fn ifpromisc ,
1234but for the all-multicasts
1235.Pq Dv IFF_ALLMULTI
1236flag instead of the promiscuous flag.
1237.It Fn ifunit
1238Return an
1239.Vt ifnet
1240pointer for the interface named
1241.Fa name .
1242.It Fn ifunit_ref
1243Return a reference-counted (via
1244.Fn ifa_ref )
1245.Vt ifnet
1246pointer for the interface named
1247.Fa name .
1248This is the preferred function over
1249.Fn ifunit .
1250The caller is responsible for releasing the reference with
1251.Fn if_rele
1252when it is finished with the ifnet.
1253.It Fn ifioctl
1254Process the ioctl request
1255.Fa cmd ,
1256issued on socket
1257.Fa so
1258by thread
1259.Fa td ,
1260with data parameter
1261.Fa data .
1262This is the main routine for handling all interface configuration
1263requests from user mode.
1264It is ordinarily only called from the socket-layer
1265.Xr ioctl 2
1266handler, and only for commands with class
1267.Sq Li i .
1268Any unrecognized commands will be passed down to socket
1269.Fa so Ns 's
1270protocol for
1271further interpretation.
1272The following commands are handled by
1273.Fn ifioctl :
1274.Pp
1275.Bl -tag -width ".Dv SIOCGIFNETMASK" -offset indent -compact
1276.It Dv SIOCGIFCONF
1277Get interface configuration.
1278(No call-down to driver.)
1279.Pp
1280.It Dv SIOCSIFNAME
1281Set the interface name.
1282.Dv RTM_IFANNOUNCE
1283departure and arrival messages are sent so that
1284routing code that relies on the interface name will update its interface
1285list.
1286Caller must have appropriate privilege.
1287(No call-down to driver.)
1288.It Dv SIOCGIFCAP
1289.It Dv SIOCGIFFIB
1290.It Dv SIOCGIFFLAGS
1291.It Dv SIOCGIFMETRIC
1292.It Dv SIOCGIFMTU
1293.It Dv SIOCGIFPHYS
1294Get interface capabilities, FIB, flags, metric, MTU, medium selection.
1295(No call-down to driver.)
1296.Pp
1297.It Dv SIOCSIFCAP
1298Enable or disable interface capabilities.
1299Caller must have appropriate privilege.
1300Before a call to the driver-specific
1301.Fn if_ioctl
1302routine, the requested mask for enabled capabilities is checked
1303against the mask of capabilities supported by the interface,
1304.Va if_capabilities .
1305Requesting to enable an unsupported capability is invalid.
1306The rest is supposed to be done by the driver,
1307which includes updating
1308.Va if_capenable
1309and
1310.Va if_data.ifi_hwassist
1311appropriately.
1312.Pp
1313.It Dv SIOCSIFFIB
1314Sets interface FIB.
1315Caller must have appropriate privilege.
1316FIB values start at 0 and values greater or equals than
1317.Va net.fibs
1318are considered invalid.
1319.It Dv SIOCSIFFLAGS
1320Change interface flags.
1321Caller must have appropriate privilege.
1322If a change to the
1323.Dv IFF_UP
1324flag is requested,
1325.Fn if_up
1326or
1327.Fn if_down
1328is called as appropriate.
1329Flags listed in
1330.Dv IFF_CANTCHANGE
1331are masked off, and the field
1332.Va if_flags
1333in the interface structure is updated.
1334Finally, the driver
1335.Fn if_ioctl
1336routine is called to perform any setup
1337requested.
1338.Pp
1339.It Dv SIOCSIFMETRIC
1340.It Dv SIOCSIFPHYS
1341Change interface metric or medium.
1342Caller must have appropriate privilege.
1343.Pp
1344.It Dv SIOCSIFMTU
1345Change interface MTU.
1346Caller must have appropriate privilege.
1347MTU
1348values less than 72 or greater than 65535 are considered invalid.
1349The driver
1350.Fn if_ioctl
1351routine is called to implement the change; it is responsible for any
1352additional sanity checking and for actually modifying the MTU in the
1353interface structure.
1354.Pp
1355.It Dv SIOCADDMULTI
1356.It Dv SIOCDELMULTI
1357Add or delete permanent multicast group memberships on the interface.
1358Caller must have appropriate privilege.
1359The
1360.Fn if_addmulti
1361or
1362.Fn if_delmulti
1363function is called to perform the operation; qq.v.
1364.Pp
1365.It Dv SIOCAIFADDR
1366.It Dv SIOCDIFADDR
1367The socket's protocol control routine is called to implement the
1368requested action.
1369.El
1370.El
1371.Pp
1372.Fn if_down ,
1373.Fn ifioctl ,
1374.Fn ifpromisc ,
1375and
1376.Fn if_up
1377must be called at
1378.Fn splnet
1379or higher.
1380.Ss "Interface Address Functions"
1381Several functions exist to look up an interface address structure
1382given an address.
1383.Fn ifa_ifwithaddr
1384returns an interface address with either a local address or a
1385broadcast address precisely matching the parameter
1386.Fa addr .
1387.Fn ifa_ifwithdstaddr
1388returns an interface address for a point-to-point interface whose
1389remote
1390.Pq Dq destination
1391address is
1392.Fa addr
1393and a fib is
1394.Fa fib .
1395If
1396.Fa fib
1397is
1398.Dv RT_ALL_FIBS ,
1399then the first interface address matching
1400.Fa addr
1401will be returned.
1402.Pp
1403.Fn ifa_ifwithnet
1404returns the most specific interface address which matches the
1405specified address,
1406.Fa addr ,
1407subject to its configured netmask, or a point-to-point interface
1408address whose remote address is
1409.Fa addr
1410if one is found.
1411If
1412.Fa ignore_ptp
1413is true, skip point-to-point interface addresses.  The
1414.Fa fib
1415parameter is handled the same way as by
1416.Fn ifa_ifwithdstaddr .
1417.Pp
1418.Fn ifaof_ifpforaddr
1419returns the most specific address configured on interface
1420.Fa ifp
1421which matches address
1422.Fa addr ,
1423subject to its configured netmask.
1424If the interface is
1425point-to-point, only an interface address whose remote address is
1426precisely
1427.Fa addr
1428will be returned.
1429.Pp
1430.Fn ifaddr_byindex
1431returns the link-level address of the interface with the given index
1432.Fa idx .
1433.Pp
1434All of these functions return a null pointer if no such address can be
1435found.
1436.Ss "Interface Multicast Address Functions"
1437The
1438.Fn if_addmulti ,
1439.Fn if_delmulti ,
1440and
1441.Fn if_findmulti
1442functions provide support for requesting and relinquishing multicast
1443group memberships, and for querying an interface's membership list,
1444respectively.
1445The
1446.Fn if_addmulti
1447function takes a pointer to an interface,
1448.Fa ifp ,
1449and a generic address,
1450.Fa sa .
1451It also takes a pointer to a
1452.Vt "struct ifmultiaddr *"
1453which is filled in on successful return with the address of the
1454group membership control block.
1455The
1456.Fn if_addmulti
1457function performs the following four-step process:
1458.Bl -enum -offset indent
1459.It
1460Call the interface's
1461.Fn if_resolvemulti
1462entry point to determine the link-layer address, if any, corresponding
1463to this membership request, and also to give the link layer an
1464opportunity to veto this membership request should it so desire.
1465.It
1466Check the interface's group membership list for a pre-existing
1467membership for this group.
1468If one is not found, allocate a new one;
1469if one is, increment its reference count.
1470.It
1471If the
1472.Fn if_resolvemulti
1473routine returned a link-layer address corresponding to the group,
1474repeat the previous step for that address as well.
1475.It
1476If the interface's multicast address filter needs to be changed
1477because a new membership was added, call the interface's
1478.Fn if_ioctl
1479routine
1480(with a
1481.Fa cmd
1482argument of
1483.Dv SIOCADDMULTI )
1484to request that it do so.
1485.El
1486.Pp
1487The
1488.Fn if_delmulti
1489function, given an interface
1490.Fa ifp
1491and an address,
1492.Fa sa ,
1493reverses this process.
1494Both functions return zero on success, or a
1495standard error number on failure.
1496.Pp
1497The
1498.Fn if_findmulti
1499function examines the membership list of interface
1500.Fa ifp
1501for an address matching
1502.Fa sa ,
1503and returns a pointer to that
1504.Vt "struct ifmultiaddr"
1505if one is found, else it returns a null pointer.
1506.Sh SEE ALSO
1507.Xr ioctl 2 ,
1508.Xr link_addr 3 ,
1509.Xr queue 3 ,
1510.Xr sysctl 3 ,
1511.Xr bpf 4 ,
1512.Xr ifmib 4 ,
1513.Xr lo 4 ,
1514.Xr netintro 4 ,
1515.Xr polling 4 ,
1516.Xr config 8 ,
1517.Xr ppp 8 ,
1518.Xr mbuf 9 ,
1519.Xr rtentry 9
1520.Rs
1521.%A Gary R. Wright
1522.%A W. Richard Stevens
1523.%B TCP/IP Illustrated
1524.%V Vol. 2
1525.%O Addison-Wesley, ISBN 0-201-63354-X
1526.Re
1527.Sh AUTHORS
1528This manual page was written by
1529.An Garrett A. Wollman .
1530