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.Dd June 8, 2004
.Os
.Dt IFNET 9
.Sh NAME
.Nm ifnet ,
.Nm ifaddr ,
.Nm ifqueue ,
.Nm if_data
.Nd kernel interfaces for manipulating network interfaces
.Sh SYNOPSIS
.In sys/param.h
.In sys/time.h
.In sys/socket.h
.In net/if.h
.In net/if_var.h
.In net/if_types.h
.\"
.Ss "Interface Manipulation Functions"
.Ft void
.Fn if_attach "struct ifnet *ifp"
.Ft void
.Fn if_down "struct ifnet *ifp"
.Ft int
.Fn ifioctl "struct socket *so" "u_long cmd" "caddr_t data" "struct thread *td"
.Ft int
.Fn ifpromisc "struct ifnet *ifp" "int pswitch"
.Ft int
.Fn if_allmulti "struct ifnet *ifp" "int amswitch"
.Ft "struct ifnet *"
.Fn ifunit "const char *name"
.Ft void
.Fn if_up "struct ifnet *ifp"
.\"
.Ss "Interface Address Functions"
.Ft "struct ifaddr *"
.Fn ifa_ifwithaddr "struct sockaddr *addr"
.Ft "struct ifaddr *"
.Fn ifa_ifwithdstaddr "struct sockaddr *addr"
.Ft "struct ifaddr *"
.Fn ifa_ifwithnet "struct sockaddr *addr"
.Ft "struct ifaddr *"
.Fn ifaof_ifpforaddr "struct sockaddr *addr" "struct ifnet *ifp"
.Ft void
.Fn ifafree "struct ifaddr *ifa"
.Fn IFAFREE "struct ifaddr *ifa"
.\"
.Ss "Interface Multicast Address Functions"
.Ft int
.Fn if_addmulti "struct ifnet *ifp" "struct sockaddr *sa" "struct ifmultiaddr **ifmap"
.Ft int
.Fn if_delmulti "struct ifnet *ifp" "struct sockaddr *sa"
.Ft "struct ifmultiaddr *"
.Fn ifmaof_ifpforaddr "struct sockaddr *addr" "struct ifnet *ifp"
.Ss "Output queue macros"
.Fn IF_DEQUEUE "struct ifqueue *ifq" "struct mbuf *m"
.\"
.Ss "struct ifnet Member Functions"
.Ft void
.Fn \*(lp*if_input\*(rp "struct ifnet *ifp" "struct mbuf *m"
.Ft int
.Fo \*(lp*if_output\*(rp
.Fa "struct ifnet *ifp" "struct mbuf *m"
.Fa "struct sockaddr *dst" "struct rtentry *rt"
.Fc
.Ft void
.Fn \*(lp*if_start\*(rp "struct ifnet *ifp"
.Ft int
.Fn \*(lp*if_done\*(rp "struct ifnet *ifp"
.Ft int
.Fn \*(lp*if_ioctl\*(rp "struct ifnet *ifp" "int cmd" "caddr_t data"
.Ft void
.Fn \*(lp*if_watchdog\*(rp "struct ifnet *ifp"
.Ft int
.Fn \*(lp*if_poll_recv\*(rp "struct ifnet *ifp" "int *quotap"
.Ft int
.Fn \*(lp*if_poll_xmit\*(rp "struct ifnet *ifp" "int *quotap"
.Ft void
.Fn \*(lp*if_poll_inttrn\*(rp "struct ifnet *ifp"
.Ft void
.Fn \*(lp*if_poll_slowinput\*(rp "struct ifnet *ifp" "struct mbuf *m"
.Ft void
.Fn \*(lp*if_init\*(rp "void *if_softc"
.Ft int
.Fo \*(lp*if_resolvemulti\*(rp
.Fa "struct ifnet *ifp" "struct sockaddr **retsa" "struct sockaddr *addr"
.Fc
.Ss "struct ifaddr member function"
.Ft void
.Fo \*(lp*ifa_rtrequest\*(rp
.Fa "int cmd" "struct rtentry *rt" "struct sockaddr *dst"
.Fc
.\"
.Ss "Global Variables"
.Vt extern struct ifnethead ifnet ;
.Vt extern struct ifaddr **ifnet_addrs ;
.Vt extern int if_index ;
.Vt extern int ifqmaxlen ;
.Sh DATA STRUCTURES
The kernel mechanisms for handling network interfaces reside primarily
in the
.Vt ifnet , if_data , ifaddr ,
and
.Vt ifmultiaddr
structures in
.In net/if.h
and
.In net/if_var.h
and the functions named above and defined in
.Pa /sys/net/if.c .
Those interfaces which are intended to be used by user programs
are defined in
.In net/if.h ;
these include the interface flags, the
.Vt if_data
structure, and the structures defining the appearance of
interface-related messages on the
.Xr route 4
routing socket and in
.Xr sysctl 3 .
The header file
.In net/if_var.h
defines the kernel-internal interfaces, including the
.Vt ifnet , ifaddr ,
and
.Vt ifmultiaddr
structures and the functions which manipulate them.
(A few user programs will need
.In net/if_var.h
because it is the prerequisite of some other header file like
.In netinet/if_ether.h .
Most references to those two files in particular can be replaced by
.In net/ethernet.h . )
.Pp
The system keeps a linked list of interfaces using the
.Li TAILQ
macros defined in
.Xr queue 3 ;
this list is headed by a
.Vt "struct ifnethead"
called
.Va ifnet .
The elements of this list are of type
.Vt "struct ifnet" ,
and most kernel routines which manipulate interface as such accept or
return pointers to these structures.
Each interface structure
contains an
.Vt if_data
structure, which contains statistics and identifying information used
by management programs, and which is exported to user programs by way
of the
.Xr ifmib 4
branch of the
.Xr sysctl 3
MIB.
Each interface also has a
.Li TAILQ
of interface addresses, described by
.Vt ifaddr
structures; the head of the queue is always an
.Dv AF_LINK
address
(see
.Xr link_addr 3 )
describing the link layer implemented by the interface (if any).
(Some trivial interfaces do not provide any link layer addresses;
this structure, while still present, serves only to identify the
interface name and index.)
.Pp
Finally, those interfaces supporting reception of multicast datagrams
have a
.Li TAILQ
of multicast group memberships, described by
.Vt ifmultiaddr
structures.
These memberships are reference-counted.
.Pp
Interfaces are also associated with an output queue, defined as a
.Vt "struct ifqueue" ;
this structure is used to hold packets while the interface is in the
process of sending another.
.Pp
.Ss The Vt ifnet Ss structure
The fields of
.Vt "struct ifnet"
are as follows:
.Bl -tag -width ".Va if_capabilities" -offset indent
.It Va if_softc
.Pq Vt "void *"
A pointer to the driver's private state block.
(Initialized by driver.)
.It Va if_link
.Pq Fn TAILQ_ENTRY ifnet
.Xr queue 3
macro glue.
.It Va if_xname
.Pq Vt "char *"
The name of the interface,
(e.g.,
.Dq Li fxp0
or
.Dq Li lo0 ) .
(Initialized by driver.)
.It Va if_dname
.Pq Vt "const char *"
The name of the driver.
(Initialized by driver.)
.It Va if_dunit
.Pq Vt int
A unique number assigned to each interface managed by a particular
driver.
Drivers may choose to set this to
.Dv IF_DUNIT_NONE
if a unit number is not associated with the device.
(Initialized by driver.)
.It Va if_addrhead
.Pq Vt "struct ifaddrhead"
The head of the
.Xr queue 3
.Li TAILQ
containing the list of addresses assigned to this interface.
.It Va if_pcount
.Pq Vt int
A count of promiscuous listeners on this interface, used to
reference-count the
.Dv IFF_PROMISC
flag.
.It Va if_bpf
.Pq Vt "struct bpf_if *"
Opaque per-interface data for the packet filter,
.Xr bpf 4 .
(Initialized by
.Fn bpf_attach . )
.It Va if_index
.Pq Vt u_short
A unique number assigned to each interface in sequence as it is
attached.
This number can be used in a
.Vt "struct sockaddr_dl"
to refer to a particular interface by index
(see
.Xr link_addr 3 ) .
.It Va if_timer
.Pq Vt short
Number of seconds until the watchdog timer
.Fn if_watchdog
is called, or zero if the timer is disabled.
(Set by driver,
decremented by generic watchdog code.)
.It Va if_flags
.Pq Vt int
Flags describing operational parameters of this interface (see below).
(Manipulated by both driver and generic code.)
.It Va if_capabilities
.Pq Vt int
Flags describing the capabilities the interface supports (see below).
.It Va if_capenable
.Pq Vt int
Flags describing the enabled capabilities of the interface (see below).
.\" .It Va if_ipending
.\" Interrupt-pending bits for polled operation:
.\" .Dv IFI_XMIT
.\" (transmit complete interrupt)
.\" and
.\" .Dv IFI_RECV
.\" (received packet ready interrupt).
.\" See the
.\" .Sx Polling
.\" section, below.
.\" (Manipulated by driver.)
.It Va if_linkmib
.Pq Vt "void *"
A pointer to an interface-specific MIB structure exported by
.Xr ifmib 4 .
(Initialized by driver.)
.It Va if_linkmiblen
.Pq Vt size_t
The size of said structure.
(Initialized by driver.)
.It Va if_data
.Pq Vt "struct if_data"
More statistics and information; see
.Sx "The if_data structure" ,
below.
(Initialized by driver, manipulated by both driver and generic
code.)
.It Va if_snd
.Pq Vt "struct ifqueue"
The output queue.
(Manipulated by driver.)
.\".It Va if_poll_slowq
.\".Pq Vt "struct ifqueue *"
.\"A pointer to the input queue for devices which do not support polling
.\"well.
.\"See the
.\".Sx Polling
.\"section, below.
.\"(Initialized by driver.)
.El
.Pp
There are in addition a number of function pointers which the driver
must initialize to complete its interface with the generic interface
layer:
.Bl -ohang -offset indent
.It Fn if_input
Pass a packet to an appropriate upper layer as determined
from the link-layer header of the packet.
This routine is to be called from an interrupt handler or
used to emulate reception of a packet on this interface.
A single function implementing
.Fn if_input
can be shared among multiple drivers utilizing the same link-layer
framing, e.g., Ethernet.
.It Fn if_output
Output a packet on interface
.Fa ifp ,
or queue it on the output queue if the interface is already active.
.It Fn if_start
Start queued output on an interface.
This function is exposed in
order to provide for some interface classes to share a
.Fn if_output
among all drivers.
.Fn if_start
may only be called when the
.Dv IFF_OACTIVE
flag is not set.
(Thus,
.Dv IFF_OACTIVE
does not literally mean that output is active, but rather that the
device's internal output queue is full.)
.It Fn if_done
Not used.
We are not even sure what it was ever for.
The prototype is faked.
.It Fn if_ioctl
Process interface-related
.Xr ioctl 2
requests
(defined in
.In sys/sockio.h ) .
Preliminary processing is done by the generic routine
.Fn ifioctl
to check for appropriate privileges, locate the interface being
manipulated, and perform certain generic operations like twiddling
flags and flushing queues.
See the description of
.Fn ifioctl
below for more information.
.It Fn if_watchdog
Routine called by the generic code when the watchdog timer,
.Va if_timer ,
expires.
Usually this will reset the interface.
.\" .It Fn if_poll_recv
.\" .It Fn if_poll_xmit
.\" .It Fn if_poll_slowinput
.\" .It Fn if_poll_intren
.\" See the
.\" .Sx Polling
.\" section, below.
.It Fn if_init
Initialize and bring up the hardware,
e.g., reset the chip and the watchdog timer and enable the receiver unit.
Should mark the interface running,
but not active
.Dv ( IFF_RUNNING , ~IIF_OACTIVE ) .
.It Fn if_resolvemulti
Check the requested multicast group membership,
.Fa addr ,
for validity, and if necessary compute a link-layer group which
corresponds to that address which is returned in
.Fa *retsa .
Returns zero on success, or an error code on failure.
.El
.Ss "Interface Flags"
Interface flags are used for a number of different purposes.
Some
flags simply indicate information about the type of interface and its
capabilities; others are dynamically manipulated to reflect the
current state of the interface.
Flags of the former kind are marked
.Aq S
in this table; the latter are marked
.Aq D .
.Pp
The macro
.Dv IFF_CANTCHANGE
defines the bits which cannot be set by a user program using the
.Dv SIOCSIFFLAGS
command to
.Xr ioctl 2 ;
these are indicated by an asterisk
.Pq Ql *
in the following listing.
.Pp
.Bl -tag -width ".Dv IFF_POINTOPOINT" -offset indent -compact
.It Dv IFF_UP
.Aq D
The interface has been configured up by the user-level code.
.It Dv IFF_BROADCAST
.Aq S*
The interface supports broadcast.
.It Dv IFF_DEBUG
.Aq D
Used to enable/disable driver debugging code.
.It Dv IFF_LOOPBACK
.Aq S
The interface is a loopback device.
.It Dv IFF_POINTOPOINT
.Aq S*
The interface is point-to-point;
.Dq broadcast
address is actually the address of the other end.
.It Dv IFF_RUNNING
.Aq D*
The interface has been configured and dynamic resources were
successfully allocated.
Probably only useful internal to the
interface.
.It Dv IFF_NOARP
.Aq D
Disable network address resolution on this interface.
.It Dv IFF_PROMISC
.Aq D*
This interface is in promiscuous mode.
.It Dv IFF_PPROMISC
.Aq D
This interface is in the permanently promiscuous mode (implies
.Dv IFF_PROMISC ) .
.It Dv IFF_ALLMULTI
.Aq D*
This interface is in all-multicasts mode (used by multicast routers).
.It Dv IFF_OACTIVE
.Aq D*
The interface's hardware output queue (if any) is full; output packets
are to be queued.
.It Dv IFF_SIMPLEX
.Aq S*
The interface cannot hear its own transmissions.
.It Dv IFF_LINK0
.It Dv IFF_LINK1
.It Dv IFF_LINK2
.Aq D
Control flags for the link layer.
(Currently abused to select among
multiple physical layers on some devices.)
.It Dv IFF_MULTICAST
.Aq S*
This interface supports multicast.
.It Dv IFF_POLLING
.Aq D*
The interface is in
.Xr polling 4
mode.
See
.Sx Interface Capabilities Flags
for details.
.El
.Ss "Interface Capabilities Flags"
Interface capabilities are specialized features an interface may
or may not support.
These capabilities are very hardware-specific
and allow, when enabled,
to offload specific network processing to the interface
or to offer a particular feature for use by other kernel parts.
.Pp
It should be stressed that a capability can be completely
uncontrolled (i.e., stay always enabled with no way to disable it)
or allow limited control over itself (e.g., depend on another
capability's state.)
Such peculiarities are determined solely by the hardware and driver
of a particular interface.
Only the driver possesses
the knowledge on whether and how the interface capabilities
can be controlled.
Consequently, capabilities flags in
.Va if_capenable
should never be modified directly by kernel code other than
the interface driver.
The command
.Dv SIOCSIFCAP
to
.Fn ifioctl
is the dedicated means to attempt altering
.Va if_capenable
on an interface.
Userland code shall use
.Xr ioctl 2 .
.Pp
The following capabilities are currently supported by the system:
.Bl -tag -width ".Dv IFCAP_VLAN_HWTAGGING" -offset indent
.It Dv IFCAP_NETCONS
This interface can be a network console.
.It Dv IFCAP_POLLING
This interface supports
.Xr polling 4 .
See below for details.
.It Dv IFCAP_RXCSUM
This interface can do checksum validation on receiving data.
Some interfaces do not have sufficient buffer storage to store frames
above a certain MTU-size completely.
The driver for the interface might disable hardware checksum validation
if the MTU is set above the hardcoded limit.
.It Dv IFCAP_TXCSUM
This interface can do checksum calculation on transmitting data.
.It Dv IFCAP_HWCSUM
A shorthand for
.Pq Dv IFCAP_RXCSUM | IFCAP_TXCSUM .
.It Dv IFCAP_VLAN_HWTAGGING
This interface can do VLAN tagging on output and
demultiplex frames by their VLAN tag on input.
.It Dv IFCAP_VLAN_MTU
The
.Xr vlan 4
driver can operate over this interface in software tagging mode
without having to decrease MTU on
.Xr vlan 4
interfaces below 1500 bytes.
This implies the ability of this interface to cope with frames somewhat
longer than permitted by the Ethernet specification.
.It Dv IFCAP_JUMBO_MTU
This Ethernet interface can transmit and receive frames up to
9000 bytes long.
.El
.Pp
The ability of advanced network interfaces to offload certain
computational tasks from the host CPU to the board is limited
mostly to TCP/IP.
Therefore a separate field associated with an interface
(see
.Va ifnet.if_data.ifi_hwassist
below)
keeps a detailed description of its enabled capabilities
specific to TCP/IP processing.
The TCP/IP module consults the field to see which tasks
can be done on an
.Em outgoing
packet by the interface.
The flags defined for that field are a superset of those for
.Va mbuf.m_pkthdr.csum_flags ,
namely:
.Bl -tag -width ".Dv CSUM_FRAGMENT" -offset indent
.It Dv CSUM_IP
The interface will compute IP checksums.
.It Dv CSUM_TCP
The interface will compute TCP checksums.
.It Dv CSUM_UDP
The interface will compute UDP checksums.
.It Dv CSUM_IP_FRAGS
The interface can compute a TCP or UDP checksum for a packet
fragmented by the host CPU.
Makes sense only along with
.Dv CSUM_TCP
or
.Dv CSUM_UDP .
.It Dv CSUM_FRAGMENT
The interface will do the fragmentation of IP packets if necessary.
The host CPU does not need to care about MTU on this interface
as long as a packet to transmit through it is an IP one and it
does not exceed the size of the hardware buffer.
.El
.Pp
An interface notifies the TCP/IP module about the tasks
the former has performed on an
.Em incoming
packet by setting the corresponding flags in the field
.Va mbuf.m_pkthdr.csum_flags
of the
.Vt mbuf chain
containing the packet.
See
.Xr mbuf 9
for details.
.Pp
The capability of a network interface to operate in
.Xr polling 4
mode involves several flags in different
global variables and per-interface fields.
First, there is a system-wide
.Xr sysctl 8
master switch named
.Va kern.polling.enable ,
which can toggle
.Xr polling 4
globally.
If that variable is set to non-zero,
.Xr polling 4
will be used on those devices where it is enabled individually.
Otherwise,
.Xr polling 4
will not be used in the system.
Second, the capability flag
.Dv IFCAP_POLLING
set in interface's
.Va if_capabilities
indicates support for
.Xr polling 4
on the particular interface.
If set in
.Va if_capabilities ,
the same flag can be marked or cleared in the interface's
.Va if_capenable ,
thus initiating switch of the interface to
.Xr polling 4
mode or interrupt
mode, respectively.
The actual mode change will occur at an implementation-specific moment
in the future, e.g., during the next interrupt or
.Xr polling 4
cycle.
And finally, if the mode transition has been successful, the flag
.Dv IFF_POLLING
is marked or cleared in the interface's
.Va if_flags
to indicate the current mode of the interface.
.Ss The Vt if_data Ss Structure
In
.Bx 4.4 ,
a subset of the interface information believed to be of interest to
management stations was segregated from the
.Vt ifnet
structure and moved into its own
.Vt if_data
structure to facilitate its use by user programs.
The following elements of the
.Vt if_data
structure are initialized by the interface and are not expected to change
significantly over the course of normal operation:
.Bl -tag -width ".Va ifi_lastchange" -offset indent
.It Va ifi_type
.Pq Vt u_char
The type of the interface, as defined in
.In net/if_types.h
and described below in the
.Sx "Interface Types"
section.
.It Va ifi_physical
.Pq Vt u_char
Intended to represent a selection of physical layers on devices which
support more than one; never implemented.
.It Va ifi_addrlen
.Pq Vt u_char
Length of a link-layer address on this device, or zero if there are
none.
Used to initialized the address length field in
.Vt sockaddr_dl
structures referring to this interface.
.It Va ifi_hdrlen
.Pq Vt u_char
Maximum length of any link-layer header which might be prepended by
the driver to a packet before transmission.
The generic code computes
the maximum over all interfaces and uses that value to influence the
placement of data in
.Vt mbuf Ns s
to attempt to ensure that there is always
sufficient space to prepend a link-layer header without allocating an
additional
.Vt mbuf .
.\" (See
.\" .Xr mbuf 9 . )
.\" .It Va ifi_recvquota
.\" .Pq Vt u_char
.\" Number of packets the interface is permitted to receive at one time
.\" when in polled mode.
.\" .It Va ifi_xmitquota
.\" .Pq Vt u_char
.\" Number of packets the interface is permitted to queue for transmission
.\" at one time when in polled mode.
.\" There is some controversy over
.\" whether such a restriction makes any sense at all.
.It Va ifi_datalen
.Pq Vt u_char
Length of the
.Vt if_data
structure.
Allows some stabilization of the routing socket ABI in the face of
increases in the length of
.Vt struct ifdata .
.It Va ifi_mtu
.Pq Vt u_long
The maximum transmission unit of the medium, exclusive of any
link-layer overhead.
.It Va ifi_metric
.Pq Vt u_long
A dimensionless metric interpreted by a user-mode routing process.
.It Va ifi_baudrate
.Pq Vt u_long
The line rate of the interface, in bits per second.
.It Va ifi_hwassist
.Pq Vt u_long
A detailed interpretation of the capabilities
to offload computational tasks for
.Em outgoing
packets.
The interface driver must keep this field in accord with
the current value of
.Va if_capenable .
.It ifi_epoch
.Pq Vt time_t
The time the interface was attached or the last time the statistics
below were reset.
.Va ifi_epoch
is intended to be used to set the SNMP variable
.Va ifCounterDiscontinuityTime .
It may also be used to determine if two successive queries for an
interface of the same index have returned results for the same
interface.
.El
.Pp
The structure additionally contains generic statistics applicable to a
variety of different interface types (except as noted, all members are
of type
.Vt u_long ) :
.Bl -tag -width ".Va ifi_lastchange" -offset indent
.It Va ifi_link_state
.Pq Vt u_char
The current link state of Ethernet interfaces.
See the
.Sx Interface Link States
section for possible values.
.It Va ifi_ipackets
Number of packets received.
.It Va ifi_ierrors
Number of receive errors detected (e.g., FCS errors, DMA overruns,
etc.).
More detailed breakdowns can often be had by way of a
link-specific MIB.
.It Va ifi_opackets
Number of packets transmitted.
.It Va ifi_oerrors
Number of output errors detected (e.g., late collisions, DMA overruns,
etc.).
More detailed breakdowns can often be had by way of a
link-specific MIB.
.It Va ifi_collisions
Total number of collisions detected on output for CSMA interfaces.
(This member is sometimes [ab]used by other types of interfaces for
other output error counts.)
.It Va ifi_ibytes
Total traffic received, in bytes.
.It Va ifi_obytes
Total traffic transmitted, in bytes.
.It Va ifi_imcasts
Number of packets received which were sent by link-layer multicast.
.It Va ifi_omcasts
Number of packets sent by link-layer multicast.
.It Va ifi_iqdrops
Number of packets dropped on input.
Rarely implemented.
.It Va ifi_noproto
Number of packets received for unknown network-layer protocol.
.\" .It Va ifi_recvtiming
.\" Amount of time, in microseconds, spent to receive an average packet on
.\" this interface.
.\" See the
.\" .Sx Polling
.\" section, below.
.\" .It Va ifi_xmittiming
.\" Amount of time, in microseconds, spent to service a transmit-complete
.\" interrupt on this interface.
.\" See the
.\" .Sx Polling
.\" section, below.
.It Va ifi_lastchange
.Pq Vt "struct timeval"
The time of the last administrative change to the interface (as required
for
.Tn SNMP ) .
.El
.Ss Interface Types
The header file
.In net/if_types.h
defines symbolic constants for a number of different types of
interfaces.
The most common are:
.Pp
.Bl -tag -offset indent -width ".Dv IFT_PROPVIRTUAL" -compact
.It Dv IFT_OTHER
none of the following
.It Dv IFT_ETHER
Ethernet
.It Dv IFT_ISO88023
ISO 8802-3 CSMA/CD
.It Dv IFT_ISO88024
ISO 8802-4 Token Bus
.It Dv IFT_ISO88025
ISO 8802-5 Token Ring
.It Dv IFT_ISO88026
ISO 8802-6 DQDB MAN
.It Dv IFT_FDDI
FDDI
.It Dv IFT_PPP
Internet Point-to-Point Protocol
.Pq Xr ppp 8
.It Dv IFT_LOOP
The loopback
.Pq Xr lo 4
interface
.It Dv IFT_SLIP
Serial Line IP
.It Dv IFT_PARA
Parallel-port IP
.Pq Dq Tn PLIP
.It Dv IFT_ATM
Asynchronous Transfer Mode
.El
.Ss Interface Link States
The following link states are currently defined:
.Pp
.Bl -tag -offset indent -width ".Dv LINK_STATE_UNKNOWN" -compact
.It Dv LINK_STATE_UNKNOWN
The link is in an invalid or unknown state.
.It Dv LINK_STATE_DOWN
The link is down.
.It Dv LINK_STATE_UP
The link is up.
.El
.Ss The Vt ifaddr Ss Structure
Every interface is associated with a list
(or, rather, a
.Li TAILQ )
of addresses, rooted at the interface structure's
.Va if_addrlist
member.
The first element in this list is always an
.Dv AF_LINK
address representing the interface itself; multi-access network
drivers should complete this structure by filling in their link-layer
addresses after calling
.Fn if_attach .
Other members of the structure represent network-layer addresses which
have been configured by means of the
.Dv SIOCAIFADDR
command to
.Xr ioctl 2 ,
called on a socket of the appropriate protocol family.
The elements of this list consist of
.Vt ifaddr
structures.
Most protocols will declare their own protocol-specific
interface address structures, but all begin with a
.Vt "struct ifaddr"
which provides the most-commonly-needed functionality across all
protocols.
Interface addresses are reference-counted.
.Pp
The members of
.Vt "struct ifaddr"
are as follows:
.Bl -tag -width ".Va ifa_rtrequest" -offset indent
.It Va ifa_addr
.Pq Vt "struct sockaddr *"
The local address of the interface.
.It Va ifa_dstaddr
.Pq Vt "struct sockaddr *"
The remote address of point-to-point interfaces, and the broadcast
address of broadcast interfaces.
.Va ( ifa_broadaddr
is a macro for
.Va ifa_dstaddr . )
.It Va ifa_netmask
.Pq Vt "struct sockaddr *"
The network mask for multi-access interfaces, and the confusion
generator for point-to-point interfaces.
.It Va ifa_ifp
.Pq Vt "struct ifnet *"
A link back to the interface structure.
.It Va ifa_link
.Pq Fn TAILQ_ENTRY ifaddr
.Xr queue 3
glue for list of addresses on each interface.
.It Va ifa_rtrequest
See below.
.It Va ifa_flags
.Pq Vt u_short
Some of the flags which would be used for a route representing this
address in the route table.
.It Va ifa_refcnt
.Pq Vt short
The reference count.
.It Va ifa_metric
.Pq Vt int
A metric associated with this interface address, for the use of some
external routing protocol.
.El
.Pp
References to
.Vt ifaddr
structures are gained manually, by incrementing the
.Va ifa_refcnt
member.
References are released by calling either the
.Fn ifafree
function or the
.Fn IFAFREE
macro.
.Pp
.Fn ifa_rtrequest
is a pointer to a function which receives callouts from the routing
code
.Pq Fn rtrequest
to perform link-layer-specific actions upon requests to add, resolve,
or delete routes.
The
.Fa cmd
argument indicates the request in question:
.Dv RTM_ADD , RTM_RESOLVE ,
or
.Dv RTM_DELETE .
The
.Fa rt
argument is the route in question; the
.Fa dst
argument is the specific destination being manipulated
for
.Dv RTM_RESOLVE ,
or a null pointer otherwise.
.Sh FUNCTIONS
The functions provided by the generic interface code can be divided
into two groups: those which manipulate interfaces, and those which
manipulate interface addresses.
In addition to these functions, there
may also be link-layer support routines which are used by a number of
drivers implementing a specific link layer over different hardware;
see the documentation for that link layer for more details.
.Ss The Vt ifmultiaddr Ss Structure
Every multicast-capable interface is associated with a list of
multicast group memberships, which indicate at a low level which
link-layer multicast addresses (if any) should be accepted, and at a
high level, in which network-layer multicast groups a user process has
expressed interest.
.Pp
The elements of the structure are as follows:
.Bl -tag -width ".Va ifma_refcount" -offset indent
.It Va ifma_link
.Pq Fn LIST_ENTRY ifmultiaddr
.Xr queue 3
macro glue.
.It Va ifma_addr
.Pq Vt "struct sockaddr *"
A pointer to the address which this record represents.
The
memberships for various address families are stored in arbitrary
order.
.It Va ifma_lladdr
.Pq Vt "struct sockaddr *"
A pointer to the link-layer multicast address, if any, to which the
network-layer multicast address in
.Va ifma_addr
is mapped, else a null pointer.
If this element is non-nil, this
membership also holds an invisible reference to another membership for
that link-layer address.
.It Va ifma_refcount
.Pq Vt u_int
A reference count of requests for this particular membership.
.El
.Ss Interface Manipulation Functions
.Bl -ohang -offset indent
.It Fn if_attach
Link the specified interface
.Fa ifp
into the list of network interfaces.
Also initialize the list of
addresses on that interface, and create a link-layer
.Vt ifaddr
structure to be the first element in that list.
(A pointer to
this address structure is saved in the global array
.Va ifnet_addrs . )
.It Fn if_down
Mark the interface
.Fa ifp
as down (i.e.,
.Dv IFF_UP
is not set),
flush its output queue, notify protocols of the transition,
and generate a message from the
.Xr route 4
routing socket.
.It Fn if_up
Mark the interface
.Fa ifp
as up, notify protocols of the transition,
and generate a message from the
.Xr route 4
routing socket.
.It Fn ifpromisc
Add or remove a promiscuous reference to
.Fa ifp .
If
.Fa pswitch
is true, add a reference;
if it is false, remove a reference.
On reference count transitions
from zero to one and one to zero, set the
.Dv IFF_PROMISC
flag appropriately and call
.Fn if_ioctl
to set up the interface in the desired mode.
.It Fn if_allmulti
As
.Fn ifpromisc ,
but for the all-multicasts
.Pq Dv IFF_ALLMULTI
flag instead of the promiscuous flag.
.It Fn ifunit
Return an
.Vt ifnet
pointer for the interface named
.Fa name .
.It Fn ifioctl
Process the ioctl request
.Fa cmd ,
issued on socket
.Fa so
by thread
.Fa td ,
with data parameter
.Fa data .
This is the main routine for handling all interface configuration
requests from user mode.
It is ordinarily only called from the socket-layer
.Xr ioctl 2
handler, and only for commands with class
.Sq Li i .
Any unrecognized commands will be passed down to socket
.Fa so Ns 's
protocol for
further interpretation.
The following commands are handled by
.Fn ifioctl :
.Pp
.Bl -tag -width ".Dv OSIOCGIFNETMASK" -offset indent -compact
.It Dv SIOCGIFCONF
.It Dv OSIOCGIFCONF
Get interface configuration.
(No call-down to driver.)
.Pp
.It Dv SIOCSIFNAME
Set the interface name.
.Dv RTM_IFANNOUNCE
departure and arrival messages are sent so that
routing code that relies on the interface name will update its interface
list.
Caller must have appropriate privilege.
(No call-down to driver.)
.It Dv SIOCGIFCAP
.It Dv SIOCGIFFLAGS
.It Dv SIOCGIFMETRIC
.It Dv SIOCGIFMTU
.It Dv SIOCGIFPHYS
Get interface capabilities, flags, metric, MTU, medium selection.
(No call-down to driver.)
.Pp
.It Dv SIOCSIFCAP
Enable or disable interface capabilities.
Caller must have appropriate privilege.
Before a call to the driver-specific
.Fn if_ioctl
routine, the requested mask for enabled capabilities is checked
against the mask of capabilities supported by the interface,
.Va if_capabilities .
Requesting to enable an unsupported capability is invalid.
The rest is supposed to be done by the driver,
which includes updating
.Va if_capenable
and
.Va if_data.ifi_hwassist
appropriately.
.Pp
.It Dv SIOCSIFFLAGS
Change interface flags.
Caller must have appropriate privilege.
If a change to the
.Dv IFF_UP
flag is requested,
.Fn if_up
or
.Fn if_down
is called as appropriate.
Flags listed in
.Dv IFF_CANTCHANGE
are masked off, and the field
.Va if_flags
in the interface structure is updated.
Finally, the driver
.Fn if_ioctl
routine is called to perform any setup
requested.
.Pp
.It Dv SIOCSIFMETRIC
.It Dv SIOCSIFPHYS
Change interface metric or medium.
Caller must have appropriate privilege.
.Pp
.It Dv SIOCSIFMTU
Change interface MTU.
Caller must have appropriate privilege.
MTU
values less than 72 or greater than 65535 are considered invalid.
The driver
.Fn if_ioctl
routine is called to implement the change; it is responsible for any
additional sanity checking and for actually modifying the MTU in the
interface structure.
.Pp
.It Dv SIOCADDMULTI
.It Dv SIOCDELMULTI
Add or delete permanent multicast group memberships on the interface.
Caller must have appropriate privilege.
The
.Fn if_addmulti
or
.Fn if_delmulti
function is called to perform the operation; qq.v.
.Pp
.It Dv SIOCSIFDSTADDR
.It Dv SIOCSIFADDR
.It Dv SIOCSIFBRDADDR
.It Dv SIOCSIFNETMASK
The socket's protocol control routine is called to implement the
requested action.
.Pp
.It Dv OSIOGIFADDR
.It Dv OSIOCGIFDSTADDR
.It Dv OSIOCGIFBRDADDR
.It Dv OSIOCGIFNETMASK
The socket's protocol control routine is called to implement the
requested action.
On return,
.Vt sockaddr
structures are converted into old-style (no
.Va sa_len
member).
.El
.El
.Pp
.Fn if_down ,
.Fn ifioctl ,
.Fn ifpromisc ,
and
.Fn if_up
must be called at
.Fn splnet
or higher.
.Ss "Interface Address Functions"
Several functions exist to look up an interface address structure
given an address.
.Fn ifa_ifwithaddr
returns an interface address with either a local address or a
broadcast address precisely matching the parameter
.Fa addr .
.Fn ifa_ifwithdstaddr
returns an interface address for a point-to-point interface whose
remote
.Pq Dq destination
address is
.Fa addr .
.Pp
.Fn ifa_ifwithnet
returns the most specific interface address which matches the
specified address,
.Fa addr ,
subject to its configured netmask, or a point-to-point interface
address whose remote address is
.Fa addr
if one is found.
.Pp
.Fn ifaof_ifpforaddr
returns the most specific address configured on interface
.Fa ifp
which matches address
.Fa addr ,
subject to its configured netmask.
If the interface is
point-to-point, only an interface address whose remote address is
precisely
.Fa addr
will be returned.
.Pp
All of these functions return a null pointer if no such address can be
found.
.Ss "Interface Multicast Address Functions"
The
.Fn if_addmulti ,
.Fn if_delmulti ,
and
.Fn ifmaof_ifpforaddr
functions provide support for requesting and relinquishing multicast
group memberships, and for querying an interface's membership list,
respectively.
The
.Fn if_addmulti
function takes a pointer to an interface,
.Fa ifp ,
and a generic address,
.Fa sa .
It also takes a pointer to a
.Vt "struct ifmultiaddr *"
which is filled in on successful return with the address of the
group membership control block.
The
.Fn if_addmulti
function performs the following four-step process:
.Bl -enum -offset indent
.It
Call the interface's
.Fn if_resolvemulti
entry point to determine the link-layer address, if any, corresponding
to this membership request, and also to give the link layer an
opportunity to veto this membership request should it so desire.
.It
Check the interface's group membership list for a pre-existing
membership for this group.
If one is not found, allocate a new one;
if one is, increment its reference count.
.It
If the
.Fn if_resolvemulti
routine returned a link-layer address corresponding to the group,
repeat the previous step for that address as well.
.It
If the interface's multicast address filter needs to be changed
because a new membership was added, call the interface's
.Fn if_ioctl
routine
(with a
.Fa cmd
argument of
.Dv SIOCADDMULTI )
to request that it do so.
.El
.Pp
The
.Fn if_delmulti
function, given an interface
.Fa ifp
and an address,
.Fa sa ,
reverses this process.
Both functions return zero on success, or a
standard error number on failure.
.Pp
The
.Fn ifmaof_ifpforaddr
function examines the membership list of interface
.Fa ifp
for an address matching
.Fa addr ,
and returns a pointer to that
.Vt "struct ifmultiaddr"
if one is found, else it returns a null pointer.
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr link_addr 3 ,
.Xr queue 3 ,
.Xr sysctl 3 ,
.Xr bpf 4 ,
.Xr ifmib 4 ,
.Xr lo 4 ,
.Xr netintro 4 ,
.Xr polling 4 ,
.Xr config 8 ,
.Xr ppp 8 ,
.Xr mbuf 9 ,
.Xr rtentry 9
.Rs
.%A Gary R. Wright
.%A W. Richard Stevens
.%B TCP/IP Illustrated
.%V Vol. 2
.%O Addison-Wesley, ISBN 0-201-63354-X
.Re
.Sh AUTHORS
This manual page was written by
.An Garrett A. Wollman .