linux-kernel - Re: [PATCH] firewire: fail open() quickly if the node doesn't exist anymore

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Message-ID: <479E6A3D.3090201@s5r6.in-berlin.de>
Date:	Tue, 29 Jan 2008 00:50:21 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Jarod Wilson <jwilson@...hat.com>
CC:	linux1394-devel@...ts.sourceforge.net,
	Kristian Høgsberg 
	<krh@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] firewire: fail open() quickly if the node doesn't exist
 anymore

Jarod Wilson wrote:
> On Sunday 27 January 2008 12:21:56 pm Stefan Richter wrote:
>> Scenario:  Process A keeps the character device file of node N open.
>> N is being unplugged.  File /dev/fwN won't be destroyed as long as A
>> doesn't close it.  Now, process B opens /dev/fwN as well.  Previously
>> it would succeed but be unable to do any IO on it of course.  With this
>> patch, process B's open() will fail immediately with -ENODEV.

> Makes perfect sense to me, no problems with it in cursory testing.

Actually I have 2nd thoughts about it.  Clients should have a general
way to know that a device went away.  (I.e. distinguish I/O errors from
mere stale generation from I/O errors due to the node being gone for
good.)  I will check tomorrow if the ABI does this distinction already.
If yes, we don't need the patch.  (But might still need improvements in
libraw1394 or/and clients to fail fast when appropriate.)
-- 
Stefan Richter
-=====-==--- ---= ===-=
http://arcgraph.de/sr/
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