freebsd-skq/lib/libc/net/getifmaddrs.3

.\" Copyright (c) 2003 Bruce M. Simpson. All rights reserved.
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.Dd November 14, 2003
.Dt GETIFMADDRS 3
.Os
.Sh NAME
.Nm getifmaddrs
.Nd get multicast group memberships
.Sh SYNOPSIS
.In sys/types.h
.In sys/socket.h
.In ifaddrs.h
.Ft int
.Fn getifmaddrs "struct ifmaddrs **ifmap"
.Ft void
.Fn freeifmaddrs "struct ifmaddrs *ifmp"
.Sh DESCRIPTION
The
.Fn getifmaddrs
function stores a reference to a linked list of the multicast memberships
on the local machine in the memory referenced by
.Fa ifmap .
The list consists of
.Vt ifmaddrs
structures, as defined in the include file
.In ifaddrs.h .
The
.Vt ifmaddrs
structure contains at least the following entries:
.Bd -literal
    struct ifmaddrs   *ifma_next;     /* Pointer to next struct */
    struct sockaddr   *ifma_name;     /* Interface name (AF_LINK) */
    struct sockaddr   *ifma_addr;     /* Multicast address */
    struct sockaddr   *ifma_lladdr;   /* Link-layer translation, if any */
.Ed
.Pp
The
.Va ifma_next
field contains a pointer to the next structure on the list.
This field is
.Dv NULL
in last structure on the list.
.Pp
The
.Va ifma_name
field references an
.Dv AF_LINK
address structure, containing the name of the
interface where the membership exists.
.Pp
The
.Va ifma_addr
references the address that this membership is for.
.Pp
The
.Va ifma_lladdr
field references a link-layer translation for the protocol-level address in
.Va ifma_addr ,
if one is set, otherwise it is
.Dv NULL .
.Pp
The data returned by
.Fn getifmaddrs
is dynamically allocated and should be freed using
.Fn freeifmaddrs
when no longer needed.
.Sh RETURN VALUES
.Rv -std getifmaddrs
.Sh ERRORS
The
.Fn getifmaddrs
may fail and set
.Va errno
for any of the errors specified for the library routines
.Xr malloc 3
or
.Xr sysctl 3 .
.Sh SEE ALSO
.Xr sysctl 3 ,
.Xr networking 4 ,
.Xr ifconfig 8
.Sh HISTORY
The
.Fn getifmaddrs
function first appeared in
.Fx 5.2 .
.Sh BUGS
If both
.In net/if.h
and
.In ifaddrs.h
are being included,
.In net/if.h
.Em must
be included before
.In ifaddrs.h .