Are PF_LINK sockets supported?

[jtl]

I'm trying to read ethernet packets with a PF_LINK socket, but so far I can't even successfully open a PF_LINK socket. I haven't been able to turn up any information on how to use a PF_LINK socket, and the few references I've found to questions about how to use such a socket are invariably answered by pointing the poster in some other direction, such as using ioctl, pcap, bfp and such. Are PF_LINK sockets actually supported on FreeBSD, and if so, where might I find some information on how to use them? Thanks for any help.

My attemps fail at step one.


#include <stdlib.h>
#include <sys/socket.h>
#include <sys/types.h>

int main(void) {

int sock;

if ( (sock = socket(PF_LINK, SOCK_RAW, 0)) < 0) {
perror("socket call failed");
exit(1);
}

close (sock);

return 0;
}


This code always fails with

socket call failed: Protocol not supported

Trying other types, such as SOCK_DGRAM, don't change the result.

[SirDice]

From socket:

The currently understood formats are:

PF_LOCAL Host-internal protocols, formerly called PF_UNIX,
PF_UNIX Host-internal protocols, deprecated, use PF_LOCAL,
PF_INET Internet version 4 protocols,
PF_PUP PUP protocols, like BSP,
PF_APPLETALK AppleTalk protocols,
PF_ROUTE Internal Routing protocol,
PF_LINK Link layer interface,
PF_IPX Novell Internet Packet eXchange protocol,
PF_RTIP Help Identify RTIP packets,
PF_PIP Help Identify PIP packets,
PF_ISDN Integrated Services Digital Network,
PF_KEY Internal key-management function,
PF_INET6 Internet version 6 protocols,
PF_NATM Native ATM access,
PF_ATM ATM,
PF_NETGRAPH Netgraph sockets

[jtl]

Thanks - I learned about PF_LINK sockets from the sockets(2) (http://www.freebsd.org/cgi/man.cgi?query=socket&sektion=2&manpath=FreeBSD+9.0-RELEASE) man page. The problem for me is that I can't make it work, and can't find any example of it working. All I can find are similar questions to mine - people posting that they can't make it work. I'm hoping someone can confirm that PF_LINK sockets really are supported, and hopefully point me to some additional information, such as an example of how to open/use one.

[expl]

I don't think you can open PF_LINK socket of any type. If you need to read/write to/from a datalink layer you need to either use the bpf device directly or use libpcap for more code portability.