Yes. They allow a user to find provably who sent data to AF_UNIX sockets.
> Question/2: with stream-ish unix domain sockets, is it possible that
> more than two processes are connected? Following code from
Yes
> Also, is it possible, that during unix_stream_sendmsg unix_peer()
> changes? (i.e. I start talking to someone else during call?) If not,
> why is not other filled only once at beggining of unix_stream_sendmsg?
I dont think it could change for streams. I guess with threads it could
however.