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From: Bill Paul <wpaul@skynet.ctr.columbia.edu>
Message-Id: <199607181825.OAA14569@skynet.ctr.columbia.edu>
Subject: Re: kern/1397: can't send to a pipe
To: j@uriah.heep.sax.de
Date: Thu, 18 Jul 1996 14:25:00 -0400 (EDT)
Cc: markd@Grizzly.COM, bugs@freefall.freebsd.org
In-Reply-To: <199607181700.KAA02495@freefall.freebsd.org> from "J Wunsch" at Jul 18, 96 10:00:01 am
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Of all the gin joints in all the towns in all the world, J Wunsch had to 
walk into mine and say:
 
> The following reply was made to PR kern/1397; it has been noted by GNATS.
 
> From: J Wunsch <j@uriah.heep.sax.de>
> To: markd@Grizzly.COM
> Cc: FreeBSD-gnats-submit@freebsd.org
> Subject: Re: kern/1397: can't send to a pipe
> Date: Thu, 18 Jul 1996 18:48:35 +0200 (MET DST)
> 
>  As Mark Diekhans wrote:
>  
>  >   Pipes are implemented as sockets and this is what fstat
>  > reports. However send returns a "Socket operation on non-socket"
>  > error.  Either socket operations should work or fstat should report
>  > the file as a FIFO, not a socket.
>  
>  Pipes are no longer implemented as sockets.  Using socket operations
>  on them was illegal all the time, even if the kernel has not been
>  reporting the error.
>  
>  Pipes are no longer reported by fstat (i think this is an error, or
>  at least an omission):

[chop]

He didn't mean fstat(1), he meant fstat(2). Look at the sample source
he supplied: he's calling fstat(2) on one of the pipe descriptors
returned by pipe(2) and he says he's getting S_IFSOCK as a result.
However since John's new pipe code does not in fact (ab)use sockets,
attempts to use socket system calls on the descriptors fail. This
is a contradiction: if socket operations won't work, fstat(2) should
not identify the descriptors as S_IFSOCK.

In this case, he could replace pipe(2) with socketpair(2) in the
application, but that doesn't change the fact that fstat(2) is reporting 
a bogus result. I suppose a new type has to be added (S_IPIPE?), but
a question (in my mind at least) of compatibility with other *BSD systems.

-Bill

-- 
=============================================================================
-Bill Paul            (212) 854-6020 | System Manager, Master of Unix-Fu
Work:         wpaul@ctr.columbia.edu | Center for Telecommunications Research
Home:  wpaul@skynet.ctr.columbia.edu | Columbia University, New York City
=============================================================================
 "If you're ever in trouble, go to the CTR. Ask for Bill. He will help you."
=============================================================================