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. $addr = pack_sockaddr_nl( $pid, $groups ) Returns a "sockaddr_nl" structure with the fields packed into it. ( $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 $buffer = pack_nlmsghdr( $type, $flags, $seq, $pid, $body ) ( $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. $buffer = pack_nlmsgerr( $error, $msg ) ( $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 $!. $buffer = pack_nlattrs( %attrs ) %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