[ofiwg] AF_UNIX,SOCK_DGRAM for shared memory signaling

[Dave Goodell (dgoodell)]

Sean,

I didn't bring it up on the call because I wanted to check on a couple of semantics, but I think you could just use a single "socket(AF_UNIX,SOCK_DGRAM,0)" socket per endpoint RX context.  This should scale -- it doesn't blow up as O(P^2) like RC QPs / SOCK_STREAM sockets / named pipes would.  You could expose that UNIX domain socket fd directly to the libfabric application or you could shove it into an epoll set and then the app would be given the epoll instance's FD.

The SOCK_DGRAM should be reliable [1], preserve message boundaries, and maintain ordering.

There's some question about what the right naming scheme for the sun_path value should be.  Perhaps "/tmp/libfabric/${PID}/rx_ctx${N}" would be a reasonable starting point?  If on Linux we could use the abstract socket namespace through sticking '\0' in sun_path[0], which should help with cleanup issues.

-Dave

[1] http://man7.org/linux/man-pages/man7/unix.7.html