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man:getifaddrs

GETIFADDRS(3) Linux Programmer's Manual GETIFADDRS(3)

NAME

     getifaddrs, freeifaddrs - get interface addresses

SYNOPSIS

     #include <sys/types.h>
     #include <ifaddrs.h>
     int getifaddrs(struct ifaddrs **ifap);
     void freeifaddrs(struct ifaddrs *ifa);

DESCRIPTION

     The  getifaddrs() function creates a linked list of structures describ-
     ing the network interfaces of the local system, and stores the  address
     of  the  first item of the list in *ifap.  The list consists of ifaddrs
     structures, defined as follows:
         struct ifaddrs {
             struct ifaddrs  *ifa_next;    /* Next item in list */
             char            *ifa_name;    /* Name of interface */
             unsigned int     ifa_flags;   /* Flags from SIOCGIFFLAGS */
             struct sockaddr *ifa_addr;    /* Address of interface */
             struct sockaddr *ifa_netmask; /* Netmask of interface */
             union {
                 struct sockaddr *ifu_broadaddr;
                                  /* Broadcast address of interface */
                 struct sockaddr *ifu_dstaddr;
                                  /* Point-to-point destination address */
             }       ifa_ifu;       #define                    ifa_broadaddr
         ifa_ifu.ifu_broadaddr        #define                    ifa_dstaddr
         ifa_ifu.ifu_dstaddr
             void            *ifa_data;    /* Address-specific data */ };
     The ifa_next field contains a pointer to  the  next  structure  on  the
     list, or NULL if this is the last item of the list.
     The ifa_name points to the null-terminated interface name.
     The  ifa_flags  field  contains the interface flags, as returned by the
     SIOCGIFFLAGS ioctl(2) operation (see netdevice(7) for a list  of  these
     flags).
     The  ifa_addr  field  points  to  a  structure containing the interface
     address.  (The sa_family subfield should be consulted to determine  the
     format  of  the  address  structure.)   This  field  may contain a null
     pointer.
     The ifa_netmask field points to  a  structure  containing  the  netmask
     associated  with  ifa_addr, if applicable for the address family.  This
     field may contain a null pointer.
     Depending on whether the bit IFF_BROADCAST or IFF_POINTOPOINT is set in
     ifa_flags  (only  one  can be set at a time), either ifa_broadaddr will
     contain the broadcast address associated with ifa_addr  (if  applicable
     for  the  address  family)  or ifa_dstaddr will contain the destination
     address of the point-to-point interface.
     The ifa_data field points to a  buffer  containing  address-family-spe-
     cific  data;  this  field may be NULL if there is no such data for this
     interface.
     The data returned by getifaddrs() is dynamically allocated  and  should
     be freed using freeifaddrs() when no longer needed.

RETURN VALUE

     On  success,  getifaddrs()  returns zero; on error, -1 is returned, and
     errno is set appropriately.

ERRORS

     getifaddrs() may fail and set errno for any of the errors specified for
     socket(2),  bind(2),  getsockname(2), recvmsg(2), sendto(2), malloc(3),
     or realloc(3).

VERSIONS

     The getifaddrs() function first appeared in glibc 2.3, but before glibc
     2.3.3,  the  implementation supported only IPv4 addresses; IPv6 support
     was added in glibc 2.3.3.  Support of address families other than  IPv4
     is available only on kernels that support netlink.

ATTRIBUTES

     For   an   explanation   of   the  terms  used  in  this  section,  see
     attributes(7).
     +----------------------------+---------------+---------+
     |Interface                   | Attribute     | Value   |
     +----------------------------+---------------+---------+
     |getifaddrs(), freeifaddrs() | Thread safety | MT-Safe |
     +----------------------------+---------------+---------+

CONFORMING TO

     Not in POSIX.1.  This function first appeared in BSDi and is present on
     the BSD systems, but with  slightly  different  semantics  documented--
     returning  one  entry  per  interface,  not  per  address.   This means
     ifa_addr and other fields can actually be NULL if the interface has  no
     address,  and no link-level address is returned if the interface has an
     IP address assigned.  Also, the way of choosing either ifa_broadaddr or
     ifa_dstaddr differs on various systems.

NOTES

     The  addresses  returned  on  Linux  will  usually be the IPv4 and IPv6
     addresses assigned to the interface, but also one AF_PACKET address per
     interface  containing  lower-level  details about the interface and its
     physical layer.  In this case, the ifa_data field may contain a pointer
     to a struct rtnl_link_stats, defined in <linux/if_link.h> (in Linux 2.4
     and earlier, struct net_device_stats, defined in  <linux/netdevice.h>),
     which contains various interface attributes and statistics.

EXAMPLE

     The  program below demonstrates the use of getifaddrs(), freeifaddrs(),
     and getnameinfo(3).  Here is what we see when running this  program  on
     one system:
         $ ./a.out lo       AF_PACKET (17)
                         tx_packets =        524; rx_packets =        524
                         tx_bytes    =       38788;  rx_bytes   =      38788
         wlp3s0   AF_PACKET (17)
                         tx_packets =     108391; rx_packets =     130245
                         tx_bytes   =   30420659;  rx_bytes    =    94230014
         em1      AF_PACKET (17)
                         tx_packets =          0; rx_packets =          0
                         tx_bytes   =          0; rx_bytes   =          0 lo
         AF_INET (2)
                         address: <127.0.0.1> wlp3s0   AF_INET (2)
                         address: <192.168.235.137> lo       AF_INET6 (10)
                         address: <::1> wlp3s0   AF_INET6 (10)
                         address: <fe80::7ee9:d3ff:fef5:1a91%wlp3s0>
 Program source
      #define _GNU_SOURCE     /* To get defns of NI_MAXSERV  and  NI_MAXHOST
     */  #include  <arpa/inet.h>  #include <sys/socket.h> #include <netdb.h>
     #include <ifaddrs.h> #include <stdio.h>  #include  <stdlib.h>  #include
     <unistd.h> #include <linux/if_link.h>
     int main(int argc, char *argv[]) {
         struct ifaddrs *ifaddr, *ifa;
         int family, s, n;
         char host[NI_MAXHOST];
         if (getifaddrs(&ifaddr) == -1) {
             perror("getifaddrs");
             exit(EXIT_FAILURE);
         }
         /* Walk through linked list, maintaining head pointer so we
            can free list later */
         for (ifa = ifaddr, n = 0; ifa != NULL; ifa = ifa->ifa_next, n++) {
             if (ifa->ifa_addr == NULL)
                 continue;
             family = ifa->ifa_addr->sa_family;
             /* Display interface name and family (including symbolic
                form of the latter for the common families) */
             printf("%-8s %s (%d)\n",
                    ifa->ifa_name,
                    (family == AF_PACKET) ? "AF_PACKET" :
                    (family == AF_INET) ? "AF_INET" :
                    (family == AF_INET6) ? "AF_INET6" : "???",
                    family);
             /* For an AF_INET* interface address, display the address */
             if (family == AF_INET || family == AF_INET6) {
                 s = getnameinfo(ifa->ifa_addr,
                         (family == AF_INET) ? sizeof(struct sockaddr_in) :
                                               sizeof(struct sockaddr_in6),
                         host, NI_MAXHOST,
                         NULL, 0, NI_NUMERICHOST);
                 if (s != 0) {
                     printf("getnameinfo() failed: %s\n", gai_strerror(s));
                     exit(EXIT_FAILURE);
                 }
                 printf("\t\taddress: <%s>\n", host);
             } else if (family == AF_PACKET && ifa->ifa_data != NULL) {
                 struct rtnl_link_stats *stats = ifa->ifa_data;
                 printf("\t\ttx_packets = %10u; rx_packets = %10u\n"
                        "\t\ttx_bytes   = %10u; rx_bytes   = %10u\n",
                        stats->tx_packets, stats->rx_packets,
                        stats->tx_bytes, stats->rx_bytes);
             }
         }
         freeifaddrs(ifaddr);
         exit(EXIT_SUCCESS); }

SEE ALSO

     bind(2), getsockname(2), socket(2), packet(7), ifconfig(8)

COLOPHON

     This  page  is  part of release 4.16 of the Linux man-pages project.  A
     description of the project, information about reporting bugs,  and  the
     latest     version     of     this    page,    can    be    found    at
     https://www.kernel.org/doc/man-pages/.

GNU 2017-09-15 GETIFADDRS(3)

/data/webs/external/dokuwiki/data/pages/man/getifaddrs.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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