|if_softc||(Vt void *) A pointer to the drivers private state block. (Initialized by driver.)|
|if_l2com||(Vt void *) A pointer to the common data for the interfaces layer 2 protocol. (Initialized by if_alloc.)|
|if_link||(TAILQ_ENTRY ifnet) queue(3) macro glue.|
|if_xname||(Vt char *) The name of the interface, (e.g., "fxp0" or "lo0"). (Initialized by driver.)|
|if_dname||(Vt const char *) The name of the driver. (Initialized by driver.)|
|if_dunit||(Vt 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||(Vt struct ifaddrhead) The head of the queue(3) TAILQ containing the list of addresses assigned to this interface.|
|if_pcount||(Vt int) A count of promiscuous listeners on this interface, used to reference-count the IFF_PROMISC flag.|
|if_bpf||(Vt struct bpf_if *) Opaque per-interface data for the packet filter, bpf(4). (Initialized by bpf_attach.)|
A unique number assigned to each interface in sequence as it is
This number can be used in a
.Vt struct sockaddr_dl to refer to a particular interface by index (see link_addr(3)). (Initialized by if_alloc.)
|if_timer||(Vt 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||(Vt int) Flags describing operational parameters of this interface (see below). (Manipulated by both driver and generic code.)|
|(Vt int) Flags describing the capabilities the interface supports (see below).|
|if_capenable||(Vt int) Flags describing the enabled capabilities of the interface (see below).|
|if_linkmib||(Vt void *) A pointer to an interface-specific MIB structure exported by ifmib(4). (Initialized by driver.)|
|if_linkmiblen||(Vt size_t) The size of said structure. (Initialized by driver.)|
|if_data||(Vt 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||(Vt 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_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 if_input can be shared among multiple drivers utilizing the same link-layer framing, e.g., Ethernet.|
|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 devices internal output queue is full.)|
|if_done||Not used. We are not even sure what it was ever for. The prototype is faked.|
.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 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>.
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 following listing.
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 interfaces 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
<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 <D*> The interface is in polling(4) mode. See Interface Capabilities Flags for details.
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.
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 capabilitys 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 if_capenable should never be modified directly by kernel code other than the interface driver. The command SIOCSIFCAP to ifioctl is the dedicated means to attempt altering if_capenable on an interface. Userland code shall use ioctl(2).
The following capabilities are currently supported by the system:
IFCAP_NETCONS This interface can be a network console. IFCAP_POLLING This interface supports polling(4). See below for details. 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. IFCAP_TXCSUM This interface can do checksum calculation on transmitting data. IFCAP_HWCSUM A shorthand for (IFCAP_RXCSUM | IFCAP_TXCSUM). IFCAP_VLAN_HWTAGGING This interface can do VLAN tagging on output and demultiplex frames by their VLAN tag on input. IFCAP_VLAN_MTU The vlan(4) driver can operate over this interface in software tagging mode without having to decrease MTU on 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. IFCAP_JUMBO_MTU This Ethernet interface can transmit and receive frames up to 9000 bytes long.
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 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 outgoing packet by the interface. The flags defined for that field are a superset of those for mbuf.m_pkthdr.csum_flags, namely:
CSUM_IP The interface will compute IP checksums. CSUM_TCP The interface will compute TCP checksums. CSUM_UDP The interface will compute UDP checksums. 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 CSUM_TCP or CSUM_UDP. 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.
An interface notifies the TCP/IP module about the tasks the former has performed on an incoming packet by setting the corresponding flags in the field mbuf.m_pkthdr.csum_flags of the
.Vt mbuf chain containing the packet. See mbuf(9) for details.
The capability of a network interface to operate in polling(4) mode involves several flags in different global variables and per-interface fields. First, there is a system-wide sysctl(8) master switch named kern.polling.enable, which can toggle polling(4) globally. If that variable is set to non-zero, polling(4) will be used on those devices where it is enabled individually. Otherwise, polling(4) will not be used in the system. Second, the capability flag IFCAP_POLLING set in interfaces if_capabilities indicates support for polling(4) on the particular interface. If set in if_capabilities, the same flag can be marked or cleared in the interfaces if_capenable, thus initiating switch of the interface to 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 polling(4) cycle. And finally, if the mode transition has been successful, the flag IFF_POLLING is marked or cleared in the interfaces if_flags to indicate the current mode of the interface.
In BSD 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:
ifi_type (Vt u_char) The type of the interface, as defined in
.In net/if_types.h and described below in the Interface Types section.
ifi_physical (Vt u_char) Intended to represent a selection of physical layers on devices which support more than one; never implemented. ifi_addrlen (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.
ifi_hdrlen (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 .
ifi_datalen (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 .
ifi_mtu (Vt u_long) The maximum transmission unit of the medium, exclusive of any link-layer overhead. ifi_metric (Vt u_long) A dimensionless metric interpreted by a user-mode routing process. ifi_baudrate (Vt u_long) The line rate of the interface, in bits per second. ifi_hwassist (Vt u_long) A detailed interpretation of the capabilities to offload computational tasks for outgoing packets. The interface driver must keep this field in accord with the current value of if_capenable. ifi_epoch (Vt time_t) The system uptime when interface was attached or the statistics below were reset. This is intended to be used to set the SNMP variable 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.
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 ) :
ifi_link_state (Vt u_char) The current link state of Ethernet interfaces. See the Interface Link States section for possible values. 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 (Vt struct timeval) The time of the last administrative change to the interface (as required for SNMP).
The header file
.In 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 following link states are currently defined:
LINK_STATE_UNKNOWN The link is in an invalid or unknown state. LINK_STATE_DOWN The link is down. LINK_STATE_UP The link is up.
Every interface is associated with a list (or, rather, a TAILQ) of addresses, rooted at the interface structures 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
.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.
The members of
.Vt struct ifaddr are as follows:
ifa_addr (Vt struct sockaddr *) The local address of the interface. ifa_dstaddr (Vt 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 (Vt struct sockaddr *) The network mask for multi-access interfaces, and the confusion generator for point-to-point interfaces. ifa_ifp (Vt 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 (Vt u_short) Some of the flags which would be used for a route representing this address in the route table. ifa_refcnt (Vt short) The reference count. ifa_metric (Vt int) A metric associated with this interface address, for the use of some external routing protocol.
.Vt 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.
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 (Vt struct sockaddr *) A pointer to the address which this record represents. The memberships for various address families are stored in arbitrary order. ifma_lladdr (Vt 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 (Vt u_int) A reference count of requests for this particular membership.
if_alloc Allocate and initialize
.Vt struct ifnet . Initialization includes the allocation of an interface index and may include the allocation of a type specific structure in if_l2com.
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
.Vt ifaddr structure to be the first element in that list. (A pointer to this address structure is saved in the global array ifnet_addrs.) The ifp must have been allocated by if_alloc.
if_detach Shut down and unlink the specified ifp from the interface list. if_free Free the given ifp back to the system. The interface must have been previously detached if it was ever attached. if_free_type Identical to if_free except that the given type is used to free if_l2com instead of the type in if_type. This is intended for use with drivers that change their interface type. 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
.Vt 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:
Get interface configuration. (No call-down to driver.)
SIOCSIFNAME Set the interface name. 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.) SIOCGIFCAP
Get interface capabilities, flags, metric, MTU, medium selection. (No call-down to driver.)
SIOCSIFCAP Enable or disable interface capabilities. Caller must have appropriate privilege. Before a call to the driver-specific if_ioctl routine, the requested mask for enabled capabilities is checked against the mask of capabilities supported by the interface, if_capabilities. Requesting to enable an unsupported capability is invalid. The rest is supposed to be done by the driver, which includes updating if_capenable and if_data.ifi_hwassist appropriately.
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 field if_flags in the interface structure is updated. Finally, the driver if_ioctl routine is called to perform any setup requested.
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.
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.
The sockets protocol control routine is called to implement the requested action.
The sockets protocol control routine is called to implement the requested action. On return,
.Vt 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.
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.
The if_addmulti, if_delmulti, and ifmaof_ifpforaddr functions provide support for requesting and relinquishing multicast group memberships, and for querying an interfaces 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
.Vt 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:
- Call the interfaces 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.
- Check the interfaces 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.
- If the if_resolvemulti routine returned a link-layer address corresponding to the group, repeat the previous step for that address as well.
- If the interfaces multicast address filter needs to be changed because a new membership was added, call the interfaces 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
.Vt 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), polling(4), config(8), ppp(8), mbuf(9), rtentry(9)
This manual page was written by
.An Garrett A. Wollman .
|March 14, 2007||IFNET (9)|