NAME

   Socket::Netlink - interface to Linux's PF_NETLINK socket family

SYNOPSIS

    use Socket;
    use Socket::Netlink qw( :DEFAULT pack_nlmsghdr unpack_nlmsghdr );

    socket( my $sock, PF_NETLINK, SOCK_RAW, 0 ) or die "socket: $!";

    send( $sock, pack_nlmsghdr( 18, NLM_F_REQUEST|NLM_F_DUMP, 0, 0,
         "\0\0\0\0\0\0\0\0" ), 0 )
       or die "send: $!";

    recv( $sock, my $buffer, 65536, 0 ) or die "recv: $!";

    printf "Received type=%d flags=%x:\n%v02x\n",
       ( unpack_nlmsghdr( $buffer ) )[ 0, 1, 4 ];

DESCRIPTION

   This module contains the low-level constants and structure handling
   functions required to use Linux's PF_NETLINK socket family. It is
   suggested to use the high-level object interface to this instead; see
   IO::Socket::Netlink.

CONSTANTS

   The following constants are exported

   PF_NETLINK

     The packet family (for socket() calls)

   AF_NETLINK

     The address family

ADDRESS FUNCTIONS

   The following pair of functions operate on AF_NETLINK address
   structures. The meainings of the parameters are:

   pid

     The unique endpoint number for this netlink socket. If given as 0 to
     the bind() syscall, the kernel will allocate an endpoint number of
     the process's PID.

   groups

     A 32-bit bitmask of the multicast groups to join.

pack_sockaddr_nl

      $addr = pack_sockaddr_nl( $pid, $groups )

   Returns a sockaddr_nl structure with the fields packed into it.

unpack_sockaddr_nl

      ( $pid, $groups ) = unpack_sockaddr_nl( $addr )

   Takes a sockaddr_nl structure and returns the unpacked fields from it.

STRUCTURE FUNCTIONS

   The following function pairs operate on structure types used by netlink

pack_nlmsghdr

      $buffer = pack_nlmsghdr( $type, $flags, $seq, $pid, $body )

unpack_nlmsghdr

      ( $type, $flags, $seq, $pid, $body, $morebuffer ) = unpack_nlmsghdr( $buffer )

   Pack or unpack a struct nlmsghdr and its payload body.

   Because a single netlink message can contain more than payload body,
   the unpack_nlmsghdr function will return the remaining buffer after
   unpacking the first message, in case there are others. If there are no
   more, the $morebuffer list element will not be returned.

    while( defined $buffer ) {
       ( my ( $type, $flags, $seq, $pid, $body ), $buffer ) = unpack_nlmsghdr( $buffer );
       ...
    }

   There is no similar functionallity for pack_nlmsghdr; simply
   concatenate multiple results together to send more than one message.

pack_nlmsgerr

      $buffer = pack_nlmsgerr( $error, $msg )

unpack_nlmsgerr

      ( $error, $msg ) = unpack_nlmsgerr( $buffer )

   Pack or unpack a struct nlmsgerr. The kernel expects or reports
   negative integers in its structures; these functions take or return
   normal positive error values suitable for use with $!.

pack_nlattrs

      $buffer = pack_nlattrs( %attrs )

unpack_nlattrs

      %attrs = unpack_nlattrs( $buffer )

   Pack or unpack a list of netlink attributes.

   These functions take or return even-sized lists of $type, $value pairs.
   The type will be the number in the netlink attribute message, and the
   value will be a plain packed string buffer. It is the caller's
   responsibilty to further pack/unpack this buffer as appropriate for the
   specific type.

   Because these functions take/return even-sized lists, they may be
   passed or returned into hashes.

SEE ALSO

     * netlink(7) - netlink - Communication between kernel and userspace
     (AF_NETLINK)

     * IO::Socket::Netlink - Object interface to AF_NETLINK domain sockets

AUTHOR

   Paul Evans <[email protected]>