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       netdevice - Low level access to Linux network devices


       #include <sys/ioctl.h>
       #include <net/if.h>


       This  man  page  describes  the  sockets  interface  which  is  used to
       configure network devices.

       Linux supports some standard ioctls to configure network devices.  They
       can be used on any socket’s file descriptor regardless of the family or
       type.  They pass an ifreq structure:

           struct ifreq {
               char ifr_name[IFNAMSIZ]; /* Interface name */
               union {
                   struct sockaddr ifr_addr;
                   struct sockaddr ifr_dstaddr;
                   struct sockaddr ifr_broadaddr;
                   struct sockaddr ifr_netmask;
                   struct sockaddr ifr_hwaddr;
                   short           ifr_flags;
                   int             ifr_ifindex;
                   int             ifr_metric;
                   int             ifr_mtu;
                   struct ifmap    ifr_map;
                   char            ifr_slave[IFNAMSIZ];
                   char            ifr_newname[IFNAMSIZ];
                   char           *ifr_data;

           struct ifconf {
               int                 ifc_len; /* size of buffer */
               union {
                   char           *ifc_buf; /* buffer address */
                   struct ifreq   *ifc_req; /* array of structures */

       Normally, the user specifies which device to affect by setting ifr_name
       to  the  name of the interface.  All other members of the structure may
       share memory.

       If an ioctl is marked as privileged then using it requires an effective
       user  ID of 0 or the CAP_NET_ADMIN capability.  If this is not the case
       EPERM will be returned.

              Given the ifr_ifindex, return  the  name  of  the  interface  in
              ifr_name.   This  is  the only ioctl which returns its result in

              Retrieve the interface index of the interface into  ifr_ifindex.

              Get  or  set  the  active  flag  word  of the device.  ifr_flags
              contains a bit mask of the following values:

                                         Device flags
              IFF_UP            Interface is running.
              IFF_BROADCAST     Valid broadcast address set.
              IFF_DEBUG         Internal debugging flag.
              IFF_LOOPBACK      Interface is a loopback interface.
              IFF_POINTOPOINT   Interface is a point-to-point link.
              IFF_RUNNING       Resources allocated.
              IFF_NOARP         No arp protocol, L2 destination address not set.
              IFF_PROMISC       Interface is in promiscuous mode.
              IFF_NOTRAILERS    Avoid use of trailers.
              IFF_ALLMULTI      Receive all multicast packets.
              IFF_MASTER        Master of a load balancing bundle.
              IFF_SLAVE         Slave of a load balancing bundle.
              IFF_MULTICAST     Supports multicast
              IFF_PORTSEL       Is able to select media type via ifmap.
              IFF_AUTOMEDIA     Auto media selection active.
              IFF_DYNAMIC       The addresses are lost when the  interface  goes
              IFF_LOWER_UP      Driver signals L1 up (since Linux 2.6.17)
              IFF_DORMANT       Driver signals dormant (since Linux 2.6.17)
              IFF_ECHO          Echo sent packets (since Linux 2.6.25)

              Setting  the active flag word is a privileged operation, but any
              process may read it.

              Get or set the metric of the device using ifr_metric.   This  is
              currently  not  implemented;  it  sets  ifr_metric  to  0 if you
              attempt to read it and returns EOPNOTSUPP if you attempt to  set

              Get  or  set  the  MTU (Maximum Transfer Unit) of a device using
              ifr_mtu.  Setting the MTU is a  privileged  operation.   Setting
              the MTU to too small values may cause kernel crashes.

              Get  or  set  the hardware address of a device using ifr_hwaddr.
              The  hardware  address  is  specified  in  a  struct   sockaddr.
              sa_family  contains  the  ARPHRD_*  device  type, sa_data the L2
              hardware address starting from byte  0.   Setting  the  hardware
              address is a privileged operation.

              Set  the hardware broadcast address of a device from ifr_hwaddr.
              This is a privileged operation.

              Get or set the interface’s hardware  parameters  using  ifr_map.
              Setting the parameters is a privileged operation.

                  struct ifmap {
                      unsigned long   mem_start;
                      unsigned long   mem_end;
                      unsigned short  base_addr;
                      unsigned char   irq;
                      unsigned char   dma;
                      unsigned char   port;

              The  interpretation of the ifmap structure depends on the device
              driver and the architecture.

              Add an address to or delete an address from  the  device’s  link
              layer  multicast filters using ifr_hwaddr.  These are privileged
              operations.  See also packet(7) for an alternative.

              Get or set the transmit queue length of a device using ifr_qlen.
              Setting the transmit queue length is a privileged operation.

              Changes  the  name  of  the  interface  specified in ifr_name to
              ifr_newname.  This  is  a  privileged  operation.   It  is  only
              allowed when the interface is not up.

              Return  a  list  of interface (transport layer) addresses.  This
              currently means only addresses of the AF_INET (IPv4) family  for
              compatibility.   The  user passes a ifconf structure as argument
              to the ioctl.  It contains  a  pointer  to  an  array  of  ifreq
              structures  in  ifc_req and its length in bytes in ifc_len.  The
              kernel fills the ifreqs with all current L3 interface  addresses
              that  are  running: ifr_name contains the interface name (eth0:1
              etc.), ifr_addr the address.  The kernel returns with the actual
              length  in  ifc_len.  If ifc_len is equal to the original length
              the buffer probably has overflowed and you should retry  with  a
              bigger  buffer  to  get all addresses.  When no error occurs the
              ioctl returns 0; otherwise -1.  Overflow is not an error.

       Most protocols support their own ioctls to configure  protocol-specific
       interface  options.  See the protocol man pages for a description.  For
       configuring IP addresses see ip(7).

       In addition  some  devices  support  private  ioctls.   These  are  not
       described here.


       Strictly speaking, SIOCGIFCONF is IP specific and belongs in ip(7).

       The  names  of  interfaces  with  no  addresses  or that don’t have the
       IFF_RUNNING flag set can be found via /proc/net/dev.

       Local IPv6 IP addresses can be found via /proc/net or via rtnetlink(7).


       glibc  2.1  is  missing  the  ifr_newname macro in <net/if.h>.  Add the
       following to your program as a workaround:

           #ifndef ifr_newname
           #define ifr_newname     ifr_ifru.ifru_slave


       proc(5), capabilities(7), ip(7), rtnetlink(7)


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