Date: 06 Sep 1999 08:36:16 +0100 From: Andrew Gierth <andrew@erlenstar.demon.co.uk> To: Alex Povolotsky <tarkhil@asteroid.svib.ru> Cc: stable@freebsd.org, hackers@freebsd.org Subject: Re: Problems with FIFO open in non-blocking mode? Message-ID: <87k8q41ogf.fsf@erlenstar.demon.co.uk> In-Reply-To: Alex Povolotsky's message of "Mon, 6 Sep 1999 09:47:32 %2B0400 (MSD)" References: <199909060547.JAA29146@shuttle.svib.ru>
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>>>>> "Alex" == Alex Povolotsky <tarkhil@asteroid.svib.ru> writes:
Alex> if ((control = open("STATUS",O_WRONLY|O_NONBLOCK))<0) {
Alex> fails to run (STATUS is pre-created FIFO file) with error
Alex> "Device not configured", which seems kinda odd for me.
Alex> However, when FIFO is opened with O_RDWR and O_NONBLOCK, every
Alex> attempt to select(2) its handler for writing doesn't wait until
Alex> someone opens FIFO for reading, but instead FIFO is ready to
Alex> write at every select.
Alex> Is it a bug or a feature?
Both are features.
The behaviour of open() in the first case is required by standards. In
the second case, the fact that the FIFO has been opened O_RDWR means
that it _is_ ready for writing, and select() is correctly returning
the fact.
--
Andrew.
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