linux-kernel - Re: O_NONBLOCK is NOOP on block devices

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Message-ID: <x49sk8ezrfq.fsf@segfault.boston.devel.redhat.com>
Date:	Fri, 05 Mar 2010 11:03:37 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	M vd S <mvds.00@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: O_NONBLOCK is NOOP on block devices

M vd S <mvds.00@...il.com> writes:

>> > > If O_NONBLOCK is meaningful whatsoever (see man page docs for
>> > > semantics) against block devices, one would expect a nonblocking io
>> >
>> > It isn't...
>>
>> Thanks for the reply. It's good to get confirmation that I am not all
>> alone in an alternate non blocking universe. The linux man pages
>> actually had me convinced O_NONBLOCK would actually keep a process
>> from blocking on device io :-)
>>
>
> You're even less alone, I'm running into the same issue just now. But
> I think I've found a way around it, see below.

I guess I should note that I've suggested nonblocking I/O for files
before:

  http://linux.derkeiler.com/Mailing-Lists/Kernel/2004-10/0290.html

I'll also note that enabling such a patch broke apps that accessed cd
burners, for example, since O_NONBLOCK had some preexisting semantics
there that I fail to recall.

Cheers,
Jeff
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