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NAME    [Toc]    [Back]

     ifnet, ifaddr, ifqueue, if_data -- kernel interfaces for manipulating
     network interfaces

SYNOPSIS    [Toc]    [Back]

     #include <sys/param.h>
     #include <sys/time.h>
     #include <sys/socket.h>
     #include <net/if.h>
     #include <net/if_var.h>
     #include <net/if_types.h>

   Interface Manipulation Functions    [Toc]    [Back]
     if_attach(struct ifnet *ifp);

     if_down(struct ifnet *ifp);

     ifioctl(struct socket *so, u_long cmd, caddr_t data, struct thread *td);

     ifpromisc(struct ifnet *ifp, int pswitch);

     if_allmulti(struct ifnet *ifp, int amswitch);

     struct ifnet *
     ifunit(const char *name);

     if_up(struct ifnet *ifp);

   Interface Address Functions    [Toc]    [Back]
     struct ifaddr *
     ifa_ifwithaddr(struct sockaddr *addr);

     struct ifaddr *
     ifa_ifwithdstaddr(struct sockaddr *addr);

     struct ifaddr *
     ifa_ifwithnet(struct sockaddr *addr);

     struct ifaddr *
     ifaof_ifpforaddr(struct sockaddr *addr, struct ifnet *ifp);

     ifafree(struct ifaddr *ifa);

     IFAFREE(struct ifaddr *ifa);

   Interface Multicast Address Functions    [Toc]    [Back]
     if_addmulti(struct ifnet *ifp, struct sockaddr *sa,
	 struct ifmultiaddr **ifmap);

     if_delmulti(struct ifnet *ifp, struct sockaddr *sa);

     struct ifmultiaddr *
     ifmaof_ifpforaddr(struct sockaddr *addr, struct ifnet *ifp);

   Output queue macros    [Toc]    [Back]
     IF_DEQUEUE(struct ifqueue *ifq, struct mbuf *m);

   struct ifnet Member Functions
     (*if_output)(struct ifnet *ifp, struct mbuf *m, struct sockaddr *dst,
	 struct rtentry *rt);

     (*if_start)(struct ifnet *ifp);

     (*if_done)(struct ifnet *ifp);

     (*if_ioctl)(struct ifnet *ifp, int cmd, caddr_t data);

     (*if_watchdog)(struct ifnet *ifp);

     (*if_poll_recv)(struct ifnet *ifp, int *quotap);

     (*if_poll_xmit)(struct ifnet *ifp, int *quotap);

     (*if_poll_inttrn)(struct ifnet *ifp);

     (*if_poll_slowinput)(struct ifnet *ifp, struct mbuf *m);

     (*if_init)(void *if_softc);

     (*if_resolvemulti)(struct ifnet *ifp, struct sockaddr **retsa,
	 struct sockaddr *addr);

   struct ifaddr member function
     (*ifa_rtrequest)(int cmd, struct rtentry *rt, struct sockaddr *dst);

   Global Variables    [Toc]    [Back]
     extern struct ifnethead ifnet;
     extern struct ifaddr **ifnet_addrs;
     extern int if_index;
     extern int ifqmaxlen;

DATA STRUCTURES    [Toc]    [Back]

     The kernel mechanisms for handling network interfaces reside primarily in
     the ifnet, if_data, ifaddr, and ifmultiaddr structures in <net/if.h> and
     <net/if_var.h> and the functions named above and defined in
     /sys/net/if.c.  Those interfaces which are intended to be used by user
     programs are defined in <net/if.h>; these include the interface flags,
     the if_data structure, and the structures defining the appearance of
     interface-related messages on the route(4) routing socket and in
     sysctl(3).  The header file <net/if_var.h> defines the kernel-internal
     interfaces, including the ifnet, ifaddr, and ifmultiaddr structures and
     the functions which manipulate them.  (A few user programs will need
     <net/if_var.h> because it is the prerequisite of some other header file
     like <netinet/if_ether.h>.  Most references to those two files in particular
 can be replaced by <net/ethernet.h>.)

     The system keeps a linked list of interfaces using the TAILQ macros
     defined in queue(3); this list is headed by a struct ifnethead called
     ifnet.  The elements of this list are of type struct ifnet, and most kernel
 routines which manipulate interface as such accept or return pointers
     to these structures.  Each interface structure contains an if_data structure,
 which contains statistics and identifying information used by management
 programs, and which is exported to user programs by way of the
     ifmib(4) branch of the sysctl(3) MIB.  Each interface also has a TAILQ of
     interface addresses, described by ifaddr structures; the head of the
     queue is always an AF_LINK address (see 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.)

     Finally, those interfaces supporting reception of multicast datagrams
     have a TAILQ of multicast group memberships, described by ifmultiaddr
     structures.  These memberships are reference-counted.

     Interfaces are also associated with an output queue, defined as a struct
     ifqueue; this structure is used to hold packets while the interface is in
     the process of sending another.

   The ifnet structure
     The fields of struct ifnet are as follows:

	   if_softc	    (void *) A pointer to the driver's private state
			    block.  (Initialized by driver.)

	   if_link	    (TAILQ_ENTRY(ifnet)) queue(3) macro glue.

	   if_xname	    (char *) The name of the interface, (e.g.,
			    ``fxp0'' or ``lo0)''.  (Initialized by driver.)

	   if_dname	    (const char *) The name of the driver.  (Initialized
 by driver.)

	   if_dunit	    (int) A unique number assigned to each interface
			    managed by a particular driver.  Drivers may
			    choose to set this to IF_DUNIT_NONE if a unit number
 is not associated with the device.  (Initialized
 by driver.)

	   if_addrhead	    (struct ifaddrhead) The head of the queue(3) TAILQ
			    containing the list of addresses assigned to this

	   if_pcount	    (int) A count of promiscuous listeners on this
			    interface, used to reference-count the IFF_PROMISC

	   if_bpf	    (struct bpf_if *) Opaque per-interface data for
			    the packet filter, bpf(4).	(Initialized by

	   if_index	    (u_short) A unique number assigned to each interface
 in sequence as it is attached.  This number
			    can be used in a struct sockaddr_dl to refer to a
			    particular interface by index (see link_addr(3)).

	   if_timer	    (short) Number of seconds until the watchdog timer
			    if_watchdog() is called, or zero if the timer is
			    disabled.  (Set by driver, decremented by generic
			    watchdog code.)

	   if_flags	    (int) Flags describing operational parameters of
			    this interface (see below).  (Manipulated by both
			    driver and generic code.)

	   if_capabilities  (int) Flags describing the capabilities the interface
 supports (see below).

	   if_capenable     (int) Flags describing the enabled capabilities of
			    the interface (see below).

	   if_linkmib	    (void *) A pointer to an interface-specific MIB
			    structure exported by ifmib(4).  (Initialized by

	   if_linkmiblen    (size_t) The size of said structure.  (Initialized
			    by driver.)

	   if_data	    (struct if_data) More statistics and information;
			    see The if_data structure, below.  (Initialized by
			    driver, manipulated by both driver and generic

	   if_snd	    (struct ifqueue) The output queue.	(Manipulated
			    by driver.)

     There are in addition a number of function pointers which the driver must
     initialize to complete its interface with the generic interface layer:

	   Output a packet on interface ifp, or queue it on the output queue
	   if the interface is already active.

	   Start queued output on an interface.  This function is exposed in
	   order to provide for some interface classes to share a if_output()
	   among all drivers.  if_start() may only be called when the
	   IFF_OACTIVE flag is not set.  (Thus, IFF_OACTIVE does not literally
	   mean that output is active, but rather that the device's internal
	   output queue is full.)

	   Not used.  We are not even sure what it was ever for.  The prototype
 is faked.

	   Process interface-related ioctl(2) requests (defined in
	   <sys/sockio.h>).  Preliminary processing is done by the generic
	   routine 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
	   ifioctl() below for more information.

	   Routine called by the generic code when the watchdog timer,
	   if_timer, expires.  Usually this will reset the interface.

	   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 (IFF_RUNNING, ~IIF_OACTIVE).

	   Check the requested multicast group membership, addr, for validity,
	   and if necessary compute a link-layer group which corresponds to
	   that address which is returned in *retsa.  Returns zero on success,
	   or an error code on failure.

   Interface Flags    [Toc]    [Back]
     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 <S> in this table;
     the latter are marked <D>.

	   IFF_UP	    <D> The interface has been configured up by the
			    user-level code.
	   IFF_BROADCAST    <S*> The interface supports broadcast.
	   IFF_DEBUG	    <D> Used to enable/disable driver debugging code.
	   IFF_LOOPBACK     <S> The interface is a loopback device.
	   IFF_POINTOPOINT  <S*> The interface is point-to-point;
			    ``broadcast'' address is actually the address of
			    the other end.
	   IFF_RUNNING	    <D*> The interface has been configured and dynamic
			    resources were successfully allocated.  Probably
			    only useful internal to the interface.
	   IFF_NOARP	    <D> Disable network address resolution on this
	   IFF_PROMISC	    <D*> This interface is in promiscuous mode.
	   IFF_PPROMISC     <D> This interface is in the permanently promiscuous
 mode (implies IFF_PROMISC).
	   IFF_ALLMULTI     <D*> This interface is in all-multicasts mode
			    (used by multicast routers).
	   IFF_OACTIVE	    <D*> The interface's hardware output queue (if
			    any) is full; output packets are to be queued.
	   IFF_SIMPLEX	    <S*> The interface cannot hear its own transmissions.

	   IFF_LINK2	    <D> Control flags for the link layer.  (Currently
			    abused to select among multiple physical layers on
			    some devices.)
	   IFF_MULTICAST    <S*> This interface supports multicast.

     The macro IFF_CANTCHANGE defines the bits which cannot be set by a user
     program using the SIOCSIFFLAGS command to ioctl(2); these are indicated
     by an asterisk in the listing above.

   Interface Capabilities Flags    [Toc]    [Back]
     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.

	   IFCAP_NETCONS  This interface can be a network console.

	   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 MTUsize
 completely.  The driver for the interface might
			  disable hardware checksum validation if the MTU is
			  set above the hardcoded limit.

	   IFCAP_TXCSUM   This interface can do checksum calculation on transmitting

   The if_data Structure
     In 4.4BSD, a subset of the interface information believed to be of interest
 to management stations was segregated from the ifnet structure and
     moved into its own if_data structure to facilitate its use by user programs.
  The following elements of the if_data structure are initialized
     by the interface and are not expected to change significantly over the
     course of normal operation:

	   ifi_type	   (u_char) The type of the interface, as defined in
			   <net/if_types.h> and described below in the
			   Interface Types section.

	   ifi_physical    (u_char) Intended to represent a selection of physical
 layers on devices which support more than one;
			   never implemented.

	   ifi_addrlen	   (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 sockaddr_dl
			   structures referring to this interface.

	   ifi_hdrlen	   (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 mbufs to attempt
			   to ensure that there is always sufficient space to
			   prepend a link-layer header without allocating an
			   additional mbuf.

	   ifi_mtu	   (u_long) The maximum transmission unit of the
			   medium, exclusive of any link-layer overhead.

	   ifi_metric	   (u_long) A dimensionless metric interpreted by a
			   user-mode routing process.

	   ifi_baudrate    (u_long) The line rate of the interface, in bits
			   per second.

     The structure additionally contains generic statistics applicable to a
     variety of different interface types (except as noted, all members are of
     type u_long):

	   ifi_ipackets    Number of packets received.

	   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

	   ifi_opackets    Number of packets transmitted.

	   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

	   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.)

	   ifi_ibytes	   Total traffic received, in bytes.

	   ifi_obytes	   Total traffic transmitted, in bytes.

	   ifi_imcasts	   Number of packets received which were sent by linklayer

	   ifi_omcasts	   Number of packets sent by link-layer multicast.

	   ifi_iqdrops	   Number of packets dropped on input.	Rarely implemented.

	   ifi_noproto	   Number of packets received for unknown networklayer

	   ifi_lastchange  (struct timeval) The time of the last administrative
 change to the interface (as required for

   Interface Types    [Toc]    [Back]
     The header file <net/if_types.h> defines symbolic constants for a number
     of different types of interfaces.	The most common are:

	   IFT_OTHER	    none of the following
	   IFT_ETHER	    Ethernet
	   IFT_ISO88023     ISO 8802-3 CSMA/CD
	   IFT_ISO88024     ISO 8802-4 Token Bus
	   IFT_ISO88025     ISO 8802-5 Token Ring
	   IFT_ISO88026     ISO 8802-6 DQDB MAN
	   IFT_PPP	    Internet Point-to-Point Protocol (ppp(8))
	   IFT_LOOP	    The loopback (lo(4)) interface
	   IFT_SLIP	    Serial Line IP
	   IFT_PARA	    Parallel-port IP (``PLIP'')
	   IFT_ATM	    Asynchronous Transfer Mode

   The ifaddr Structure
     Every interface is associated with a list (or, rather, a TAILQ) of
     addresses, rooted at the interface structure's if_addrlist member.  The
     first element in this list is always an AF_LINK address representing the
     interface itself; multi-access network drivers should complete this
     structure by filling in their link-layer addresses after calling
     if_attach().  Other members of the structure represent network-layer
     addresses which have been configured by means of the SIOCAIFADDR command
     to ioctl(2), called on a socket of the appropriate protocol family.  The
     elements of this list consist of ifaddr structures.  Most protocols will
     declare their own protocol-specific interface address structures, but all
     begin with a struct ifaddr which provides the most-commonly-needed functionality
 across all protocols.  Interface addresses are referencecounted.

     The members of struct ifaddr are as follows:

	   ifa_addr	  (struct sockaddr *) The local address of the interface.

	   ifa_dstaddr	  (struct sockaddr *) The remote address of point-topoint
 interfaces, and the broadcast address of
			  broadcast interfaces.  (ifa_broadaddr is a macro for

	   ifa_netmask	  (struct sockaddr *) The network mask for multiaccess
 interfaces, and the confusion generator for
			  point-to-point interfaces.

	   ifa_ifp	  (struct ifnet *) A link back to the interface structure.

	   ifa_link	  (TAILQ_ENTRY(ifaddr)) queue(3) glue for list of
			  addresses on each interface.

	   ifa_rtrequest  See below.

	   ifa_flags	  (u_short) Some of the flags which would be used for
			  a route representing this address in the route table.

	   ifa_refcnt	  (short) The reference count.

	   ifa_metric	  (int) A metric associated with this interface
			  address, for the use of some external routing protocol.

     References to ifaddr structures are gained manually, by incrementing the
     ifa_refcnt member.  References are released by calling either the
     ifafree() function or the IFAFREE() macro.

     ifa_rtrequest() is a pointer to a function which receives callouts from
     the routing code (rtrequest()) to perform link-layer-specific actions
     upon requests to add, resolve, or delete routes.  The cmd argument indicates
 the request in question: RTM_ADD, RTM_RESOLVE, or RTM_DELETE.  The
     rt argument is the route in question; the dst argument is the specific
     destination being manipulated for RTM_RESOLVE, or a null pointer otherwise.

FUNCTIONS    [Toc]    [Back]

     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.

   The ifmultiaddr 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.

     The elements of the structure are as follows:

	   ifma_link	  (LIST_ENTRY(ifmultiaddr)) queue(3) macro glue.

	   ifma_addr	  (struct sockaddr *) A pointer to the address which
			  this record represents.  The memberships for various
			  address families are stored in arbitrary order.

	   ifma_lladdr	  (struct sockaddr *) A pointer to the link-layer multicast
 address, if any, to which the network-layer
			  multicast address in 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.

	   ifma_refcount  (u_int) A reference count of requests for this particular

   Interface Manipulation Functions    [Toc]    [Back]
	   Link the specified interface ifp into the list of network interfaces.
  Also initialize the list of addresses on that interface,
	   and create a link-layer ifaddr structure to be the first element in
	   that list.  (A pointer to this address structure is saved in the
	   global array ifnet_addrs.)

	   Mark the interface ifp as down (i.e., IFF_UP is not set), flush its
	   output queue, notify protocols of the transition, and generate a
	   message from the route(4) routing socket.

	   Mark the interface ifp as up, notify protocols of the transition,
	   and generate a message from the route(4) routing socket.

	   Add or remove a promiscuous reference to ifp.  If 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
	   IFF_PROMISC flag appropriately and call if_ioctl() to set up the
	   interface in the desired mode.

	   As ifpromisc(), but for the all-multicasts (IFF_ALLMULTI) flag
	   instead of the promiscuous flag.

	   Return an ifnet pointer for the interface named name.

	   Process the ioctl request cmd, issued on socket so by thread td,
	   with data parameter data.  This is the main routine for handling
	   all interface configuration requests from user mode.  It is ordinarily
 only called from the socket-layer ioctl(2) handler, and only
	   for commands with class `i'.  Any unrecognized commands will be
	   passed down to socket so's protocol for further interpretation.
	   The following commands are handled by ifioctl():

		 OSIOCGIFCONF	  Get interface configuration.	(No call-down
				  to driver.)

		 SIOCGIFPHYS	  Get interface capabilities, flags, metric,
				  MTU, medium selection.  (No call-down to

		 SIOCSIFCAP	  Enable interface capabilities.  Caller must
				  have appropriate privilege.

		 SIOCSIFFLAGS	  Change interface flags.  Caller must have
				  appropriate privilege.  If a change to the
				  IFF_UP flag is requested, if_up() or
				  if_down() is called as appropriate.  Flags
				  listed in IFF_CANTCHANGE are masked off, and
				  the driver if_ioctl() routine is called to
				  perform any setup requested.

		 SIOCSIFPHYS	  Change interface metric or medium.  Caller
				  must have appropriate privilege.

		 SIOCSIFMTU	  Change interface MTU.  Caller must have
				  appropriate privilege.  MTU values less than
				  72 or greater than 65535 are considered
				  invalid.  The driver 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.

		 SIOCDELMULTI	  Add or delete permanent multicast group memberships
 on the interface.  Caller must have
				  appropriate privilege.  The if_addmulti() or
				  if_delmulti() function is called to perform
				  the operation; qq.v.

		 SIOCSIFNETMASK   The socket's protocol control routine is
				  called to implement the requested action.

		 OSIOCGIFNETMASK  The socket's protocol control routine is
				  called to implement the requested action.
				  On return, sockaddr structures are converted
				  into old-style (no sa_len member).

     if_down(), ifioctl(), ifpromisc(), and if_up() must be called at splnet()
     or higher.

   Interface Address Functions    [Toc]    [Back]
     Several functions exist to look up an interface address structure given
     an address.  ifa_ifwithaddr() returns an interface address with either a
     local address or a broadcast address precisely matching the parameter
     addr.  ifa_ifwithdstaddr() returns an interface address for a point-topoint
 interface whose remote (``destination'') address is addr.

     ifa_ifwithnet() returns the most specific interface address which matches
     the specified address, addr, subject to its configured netmask, or a
     point-to-point interface address whose remote address is addr if one is

     ifaof_ifpforaddr() returns the most specific address configured on interface
 ifp which matches address addr, subject to its configured netmask.
     If the interface is point-to-point, only an interface address whose
     remote address is precisely addr will be returned.

     All of these functions return a null pointer if no such address can be

   Interface Multicast Address Functions    [Toc]    [Back]
     The if_addmulti(), if_delmulti(), and ifmaof_ifpforaddr() functions provide
 support for requesting and relinquishing multicast group memberships,
 and for querying an interface's membership list, respectively.
     The if_addmulti() function takes a pointer to an interface, ifp, and a
     generic address, sa.  It also takes a pointer to a struct ifmultiaddr *
     which is filled in on successful return with the address of the group
     membership control block.	The if_addmulti() function performs the following
 four-step process:

	   1.	Call the interface's 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.

	   2.	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.

	   3.	If the if_resolvemulti() routine returned a link-layer address
		corresponding to the group, repeat the previous step for that
		address as well.

	   4.	If the interface's multicast address filter needs to be
		changed because a new membership was added, call the interface's
 if_ioctl() routine (with a cmd argument of
		SIOCADDMULTI) to request that it do so.

     The if_delmulti() function, given an interface ifp and an address, sa,
     reverses this process.  Both functions return zero on success, or a standard
 error number on failure.

     The ifmaof_ifpforaddr() function examines the membership list of interface
 ifp for an address matching addr, and returns a pointer to that
     struct ifmultiaddr if one is found, else it returns a null pointer.

SEE ALSO    [Toc]    [Back]

     ioctl(2), link_addr(3), queue(3), sysctl(3), bpf(4), ifmib(4), lo(4),
     netintro(4), config(8), ppp(8), rtentry(9)

     Gary R. Wright and W. Richard Stevens, TCP/IP Illustrated, Vol. 2,
     Addison-Wesley, ISBN 0-201-63354-X.

AUTHORS    [Toc]    [Back]

     This manual page was written by Garrett A. Wollman.

FreeBSD 5.2.1		       January 15, 1997 		 FreeBSD 5.2.1
[ Back ]
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