Does Linux 2.6 socket support SOCK_RDM?

thelordmule · 08-12-2007, 05:42 PM

Hi,

Ive been looking around to see if I can use the protocol

Code:

socket(*, SOCK_RDM, 0);

from the man page:
SOCK_RDM Provides a reliable datagram layer that does not guarantee ordering.

I was actually going ahead with SCTP since it also provides an orderless yet reliable delivery but thought this could soften the dev effort.

I havent found anything via my usual sources, except for the MS PGM multicast protocol (not relevant at all).

Help appreciated.

jtshaw · 08-12-2007, 06:20 PM

I believe it does. SOCK_RDM is defined in include/linux/net.h.

Code:

/**
 * enum sock_type - Socket types
 * @SOCK_STREAM: stream (connection) socket
 * @SOCK_DGRAM: datagram (conn.less) socket
 * @SOCK_RAW: raw socket
 * @SOCK_RDM: reliably-delivered message
 * @SOCK_SEQPACKET: sequential packet socket
 * @SOCK_DCCP: Datagram Congestion Control Protocol socket
 * @SOCK_PACKET: linux specific way of getting packets at the dev level.
 *                For writing rarp and other similar things on the user level.
 *
 * When adding some new socket type please
 * grep ARCH_HAS_SOCKET_TYPE include/asm-* /socket.h, at least MIPS
 * overrides this enum for binary compat reasons.
 */

thelordmule · 08-12-2007, 07:10 PM

Thanks for the quick response, but sadly it wasnt what I was looking for.

Yes, header definitions are there, however implementation seems to be missing. Here is some sample code:

Code:

#include <stdio.h>
#include <sys/socket.h>

int main()
{
	int sock_fd = socket( AF_INET, SOCK_RDM, 0 );

	perror("socket: ");

	printf("sock_fd: %d\n", sock_fd);

	return 0;
}

and its output:

Code:

socket: : Socket type not supported
sock_fd: -1

jtshaw · 08-13-2007, 06:51 AM

On further review it does appear that standard 2.6 kernels don't support SOCK_RDM... at least my 2.6.22 kernel packaged by Ubuntu doesn't.

I get an errno 94 back from the socket call which means "Socket type not supported" just like you did.

Also food for thought... I pulled out my copy of Advanced Programming in the UNIX Environment (2nd Edition by Stevens and Lago) and it does not list SOCK_RDM in the table of POSIX.1 socket types. It does say, however, that OS's are free to implement other socket types if they wish.

thelordmule · 08-13-2007, 05:10 PM

Quote:

Originally Posted by jtshaw

On further review it does appear that standard 2.6 kernels don't support SOCK_RDM... at least my 2.6.22 kernel packaged by Ubuntu doesn't.

I get an errno 94 back from the socket call which means "Socket type not supported" just like you did.

Also food for thought... I pulled out my copy of Advanced Programming in the UNIX Environment (2nd Edition by Stevens and Lago) and it does not list SOCK_RDM in the table of POSIX.1 socket types. It does say, however, that OS's are free to implement other socket types if they wish.

Nice find. I actually have that book lost in my personal jungle of literature :P

I find it interesting that after specification for socket has existed for so long no actual POSIX implementation existed, even if it were something like RUDP (RFC 1151). I wonder if anyone was willing to include such reliable UDP implementation for the kernel at any stage. Out of the many that exist out there surely a defacto standard like the Bell labs one could have been included. I'd much favour seeing something like udt3 though :P

I might be interested in actually helping support that kind of project for the kernel. Would kernel.org be the place to goto for such things?