unix domain sockets

[Chris Torek]

>In article <1990Feb23.023047.19975 at uniwa.uwa.oz>, toivo at uniwa.uwa.oz
>(Toivo Pedaste) writes:
>>When a unix domain socket is opened ... [the path name appears in the
  file system, and remains there even when the socket is defunct].
>>My question is does this now orphaned socket have a possible use or
>>does it just get in the way.

It just gets in the way.  unlink() will serve to get rid of it.

In article <6740 at decvax.dec.com> evans at testmax.ZK3.DEC.COM (Marc Evans) writes:
>This type of problem is typically due to the socket not being properly
>setup and closed down. After calling socket, it is often recommended that
>a call be made to setsockopt something like the following:
>	setsockopt(fd,SOL_SOCKET,SO_REUSEADDR,NULL,0);

SO_REUSEADDR does not apply to Unix domain sockets (see first line of
>> above).  The name space of Unix domain sockets is the file system,
and there are no `incomplete' paths in the Unix file system.
SO_REUSEADDR is intended to allow reuse of an `incomplete' name: since
a connection that spans multiple machines automatically has at least
two parts to its name (one on one machine, one on the other), and in
the Internet naming scheme these two parts must remain separate for
some time, it is possible to have duplicate `partial names'.

An Internet socket `name' is the quad <local-address, local-port,
remote-address, remote-port>.  Each unique quad names one possible
socket.  The BSD bind() call refuses to allow non-unique
<local-address, local-port> pairs `just in case', and typically
local-ports alone give a unique socket ID.  If you need non-unique
local port numbers, you can set SO_REUSEADDR.

Incidentally, the call quoted above is wrong.  The fourth and fifth
arguments to setsockopt should never be NULL and 0.  4.2BSD ignored
them; 4.3BSD does not.  To *en*able SO_REUSEADDR, use

	int on = 1;
	err = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR,
	    (caddr_t)&on, sizeof on);

To *dis*able it, use

	int off = 0;
	err = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR,
	    (caddr_t)&off, sizeof off);

A `char' may suffice, but an `int' is Officially Correct.  A nonzero
value means `turn the option on', and a zero value means `turn the
option off'.  Other options have fancier values (e.g., SO_LINGER;
SO_DONTLINGER has vanished).
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris at cs.umd.edu	Path:	uunet!mimsy!chris