ifnet, ifaddr, ifqueue, if_data -- kernel interfaces for manipulating
network interfaces
#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]
void
if_attach(struct ifnet *ifp);
void
if_down(struct ifnet *ifp);
int
ifioctl(struct socket *so, u_long cmd, caddr_t data, struct thread *td);
int
ifpromisc(struct ifnet *ifp, int pswitch);
int
if_allmulti(struct ifnet *ifp, int amswitch);
struct ifnet *
ifunit(const char *name);
void
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);
void
ifafree(struct ifaddr *ifa);
IFAFREE(struct ifaddr *ifa);
Interface Multicast Address Functions [Toc] [Back]
int
if_addmulti(struct ifnet *ifp, struct sockaddr *sa,
struct ifmultiaddr **ifmap);
int
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
int
(*if_output)(struct ifnet *ifp, struct mbuf *m, struct sockaddr *dst,
struct rtentry *rt);
void
(*if_start)(struct ifnet *ifp);
int
(*if_done)(struct ifnet *ifp);
int
(*if_ioctl)(struct ifnet *ifp, int cmd, caddr_t data);
void
(*if_watchdog)(struct ifnet *ifp);
int
(*if_poll_recv)(struct ifnet *ifp, int *quotap);
int
(*if_poll_xmit)(struct ifnet *ifp, int *quotap);
void
(*if_poll_inttrn)(struct ifnet *ifp);
void
(*if_poll_slowinput)(struct ifnet *ifp, struct mbuf *m);
void
(*if_init)(void *if_softc);
int
(*if_resolvemulti)(struct ifnet *ifp, struct sockaddr **retsa,
struct sockaddr *addr);
struct ifaddr member function
void
(*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;
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
interface.
if_pcount (int) A count of promiscuous listeners on this
interface, used to reference-count the IFF_PROMISC
flag.
if_bpf (struct bpf_if *) Opaque per-interface data for
the packet filter, bpf(4). (Initialized by
bpf_attach().)
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
driver.)
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
code.)
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:
if_output()
Output a packet on interface ifp, or queue it on the output queue
if the interface is already active.
if_start()
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.)
if_done()
Not used. We are not even sure what it was ever for. The prototype
is faked.
if_ioctl()
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.
if_watchdog()
Routine called by the generic code when the watchdog timer,
if_timer, expires. Usually this will reset the interface.
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 (IFF_RUNNING, ~IIF_OACTIVE).
if_resolvemulti()
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
interface.
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_LINK0
IFF_LINK1
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
data.
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
MIB.
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
MIB.
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
multicast.
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
protocol.
ifi_lastchange (struct timeval) The time of the last administrative
change to the interface (as required for
SNMP).
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_FDDI FDDI
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_dstaddr.)
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.
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
membership.
Interface Manipulation Functions [Toc] [Back]
if_attach()
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.)
if_down()
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.
if_up()
Mark the interface ifp as up, notify protocols of the transition,
and generate a message from the route(4) routing socket.
ifpromisc()
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.
if_allmulti()
As ifpromisc(), but for the all-multicasts (IFF_ALLMULTI) flag
instead of the promiscuous flag.
ifunit()
Return an ifnet pointer for the interface named name.
ifioctl()
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():
SIOCGIFCONF
OSIOCGIFCONF Get interface configuration. (No call-down
to driver.)
SIOCGIFCAP
SIOCGIFFLAGS
SIOCGIFMETRIC
SIOCGIFMTU
SIOCGIFPHYS Get interface capabilities, flags, metric,
MTU, medium selection. (No call-down to
driver.)
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.
SIOCSIFMETRIC
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.
SIOCADDMULTI
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.
SIOCSIFDSTADDR
SIOCSIFADDR
SIOCSIFBRDADDR
SIOCSIFNETMASK The socket's protocol control routine is
called to implement the requested action.
OSIOGIFADDR
OSIOCGIFDSTADDR
OSIOCGIFBRDADDR
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
found.
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
found.
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.
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.
This manual page was written by Garrett A. Wollman.
FreeBSD 5.2.1 January 15, 1997 FreeBSD 5.2.1 [ Back ] |
