DragonFly On-Line Manual Pages
IFNET(9) DragonFly Kernel Developer's Manual IFNET(9)
NAME
ifnet, ifaddr, ifqueue, if_data - kernel interfaces for manipulating
network interfaces
SYNOPSIS
#include <sys/types.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
void
if_attach(struct ifnet *ifp);
void
if_down(struct ifnet *ifp);
int
ifioctl(struct socket *so, u_long cmd, caddr_t data, struct proc *p);
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
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);
Interface Multicast Address Functions
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
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_input)(struct ifnet *ifp, struct mbuf *m, const struct pktinfo *pi,
int cpuid);
void
(*if_start)(struct ifnet *ifp, struct ifaltq_subque *ifsq);
int
(*if_ioctl)(struct ifnet *ifp, u_long command, caddr_t data,
struct ucred *cr);
void
(*if_watchdog)(struct ifnet *ifp);
void
(*if_init)(void *if_softc);
int
(*if_resolvemulti)(struct ifnet *ifp, struct sockaddr **retsa,
struct sockaddr *addr);
void
(*if_poll)(struct ifnet *ifp, enum poll_cmd cmd, int count);
struct ifaddr member function
void
(*ifa_rtrequest)(int cmd, struct rtentry *rt, struct sockaddr *dst);
Global Variables
extern struct ifnethead ifnet;
extern int if_index;
extern int ifqmaxlen;
DATA STRUCTURES
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 LIST 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_carp (struct carp_if *) Per-interface data for
carp(4).
if_bpf (struct bpf_if *) Opaque per-interface data for
the packet filter, bpf(4). (Initialized by
bpfattach().)
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_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 ifaltq) The output queue including
altq(4). (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_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, ~IFF_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
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.
IFF_POLLING The interface is in polling mode.
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.
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
initialize 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_link_state (u_long) The link state of the interface,
either LINK_STATE_UNKNOWN, LINK_STATE_DOWN, or
LINK_STATE_UP.
ifi_baudrate (uint64_t) 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
link-layer 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 network-
layer protocol.
ifi_lastchange (struct timeval) The time of the last
administrative change to the interface (as
required for SNMP).
Interface Types
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 reference-
counted.
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-
to-point interfaces, and the broadcast address
of broadcast interfaces. (ifa_broadaddr is a
macro for ifa_dstaddr.)
ifa_netmask (struct sockaddr *) The network mask for multi-
access interfaces, and the confusion generator
for point-to-point interfaces.
ifa_ifp (struct ifnet *) A link back to the interface
structure.
ifa_containers (struct ifaddr_container *) A pointer to an
array of ifaddr_container structures which hold
per-CPU data.
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_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 of the according ifa_containers structure (such as by
calling the IFAREF() macro). References are released by calling 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
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-
NULL, 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
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 process p,
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 Get interface configuration. (No call-
down to driver.)
SIOCGIFFLAGS
SIOCGIFMETRIC
SIOCGIFMTU
SIOCGIFPHYS Get interface flags, metric, MTU, medium
selection. (No call-down to driver.)
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.
if_down(), ifioctl(), ifpromisc(), and if_up() must be called inside a
critical section.
Interface Address Functions
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-to-
point 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
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
ioctl(2), link_addr(3), queue(3), sysctl(3), bpf(4), ifmib(4), lo(4),
netintro(4), ppp(8), rtentry(9)
Gary R. Wright and W. Richard Stevens, TCP/IP Illustrated, Vol. 2,
Addison-Wesley, ISBN 0-201-63354-X.
AUTHORS
This manual page was written by Garrett A. Wollman.
DragonFly 6.3-DEVELOPMENT June 20, 2018 DragonFly 6.3-DEVELOPMENT