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Date:      Thu, 18 Jul 1996 19:10:19 -0700 (PDT)
From:      Mark Diekhans <markd@Grizzly.COM>
To:        joerg_wunsch@uriah.heep.sax.de, Bill Paul <wpaul@skynet.ctr.columbia.edu>
Cc:        FreeBSD-gnats-submit@freebsd.org, bugs@freefall.freebsd.org
Subject:   Re: kern/1397: can't send to a pipe
Message-ID:  <199607190210.TAA00823@Grizzly.COM>
In-Reply-To: <199607181648.SAA06346@uriah.heep.sax.de> (message from J Wunsch on Thu, 18 Jul 1996 18:48:35 %2B0200 (MET DST))

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Hi J"org and Bill,

>From: J Wunsch <j@uriah.heep.sax.de>

>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.

Cool, I always though sockets were a little overkill for pipes...

>From: Bill Paul <wpaul@skynet.ctr.columbia.edu>

>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.

Exactly!


>In this case, he could replace pipe(2) with socketpair(2) in the

The code (a Tcl extension) I am dealing with has an open file descriptor and
tries to figure out what to do with it, so this isn't a solution. It uses
send on sockets since its more reliable.

>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.

Reporting FIFO would probably be better than SOCK, at least that wouldn't
lead people to do the wrong thing because they think its a socket.

Given all of this, the definition of S_ISFIFO probably is wrong as well:

#define	S_ISFIFO(m)	(((m) & 0170000) == 0010000 || \
			 ((m) & 0170000) == 0140000)	/* fifo or socket */



Mark



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