GETIFADDRS(3)

NAME
getifaddrs - get interface addresses

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

DESCRIPTION
The getifaddrs() function stores a reference to a linked list of the network interfaces on the local machine in the memory referenced by ifap. The list consists of ifaddrs structures, as defined in the include file <ifaddrs.h>. The ifaddrs structure contains at least the following entries:

        struct ifaddrs   *ifa_next;         /* Pointer to next struct */
        char             *ifa_name;         /* Interface name */
        u_int             ifa_flags;        /* Interface flags */
        struct sockaddr  *ifa_addr;         /* Interface address */
        struct sockaddr  *ifa_netmask;      /* Interface netmask */
        union {
    	struct sockaddr *ifu_broadaddr;
    	struct sockaddr *ifu_dstaddr;
        } ifa_ifu;
        void             *ifa_data;		/* Address specific data */
        #define ifa_broadaddr ifa_ifu.ifu_broadaddr  /* broadcast address */
        #define ifa_dstaddr   ifa_ifu.ifu_dstaddr    /* other end of link */

The ifa_next field contains a pointer to the next structure on the list. This field is NULL in last structure on the list.

The ifa_name field contains the interface name.

The ifa_flags field contains the interface flags, as set by ifconfig(8) utility.

The ifa_addr field references either the address of the interface or the link level address of the interface, if one exists, otherwise it is NULL. (The sa_family field of the ifa_addr field should be consulted to determine the format of the ifa_addr address.)

The ifa_netmask field references the netmask associated with ifa_addr, if one is set, otherwise it is NULL.

The ifa_broadaddr, which should only be referenced for non-P2P interfaces, references the broadcast address associated with ifa_addr, if one exists, otherwise it is NULL.

The ifa_dstaddr references the destination address on a P2P interface, if one exists, otherwise it is NULL.

Please note that the ifa_broadaddr and the ifa_dstaddr fields are unionized unlike original definition.

A variant of sockaddr structure will be used for ifa_addr, ifa_netmask, ifa_broadaddr, ifa_dstaddr; The sockaddr_in structure will be used for AF_INET addresses, sockaddr_in6 will be used for AF_INET6 addresses and sockaddr_ll will be used for AF_PACKET addresses.

The ifa_data field references address family specific data. For AF_PACKET addresses it contains a pointer to the struct net_device_stats (as defined in include file <linux/netdevice.h>) which contains various interface attributes and statistics.

The data returned by getifaddrs() is dynamically allocated and should be freed using freeifaddrs() when no longer needed.

RETURN VALUES
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.

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

BUGS
If both <net/if.h> and <ifaddrs.h> are being included, <net/if.h> must be included before <ifaddrs.h>.

SEE ALSO
socket(2), netlink(3), netlink(7), rtnetlink(3), rtnetlink(7), ifconfig(8), ip(7), ipv6(7), packet(7)

HISTORY
The getifaddrs implementation first appeared in BSDI BSD/OS. Linux version of this function was developed by YOSHIFUJI Hideaki from scratch.