linux-kernel - Re: [PATCH 3/3] Add timeout feature

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Message-ID: <20080709042147.GB20695@cynthia.pants.nu>
Date:	Tue, 8 Jul 2008 21:21:47 -0700
From:	Brad Boyer <flar@...andria.com>
To:	Theodore Tso <tytso@....edu>, Pavel Machek <pavel@...e.cz>,
	Christoph Hellwig <hch@...radead.org>,
	Takashi Sato <t-sato@...jp.nec.com>, akpm@...ux-foundation.org,
	viro@...IV.linux.org.uk,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"xfs@....sgi.com" <xfs@....sgi.com>,
	"dm-devel@...hat.com" <dm-devel@...hat.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	axboe@...nel.dk, mtk.manpages@...glemail.com
Subject: Re: [PATCH 3/3] Add timeout feature

On Tue, Jul 08, 2008 at 09:09:22PM -0400, Theodore Tso wrote:
> I had argued for the timeout (and so it's mostly my fault that
> Takashi-San included it as a feature) mainly because I was (and still
> amm) deeply paranoid about the competence of the application
> programers who might use this feature.  I could see them screwing up
> leaving it locked forever --- perhaps when their program core dumps or
> when the user types ^C and they forgot to install a signal handler,
> leaving the filesystem frozen forever.
> 
> In the meantime, user applications that try to create files on that
> filesystem, or write to files already opened when the filesystem are
> frozen will accumulate dirty pages in the page cache, until the system
> finally falls over.
> 
> Think about some of the evil perpetrated by hal and the userspace
> suspend-resume scripts (and how much complexity with random XML
> fragments getting parsed by various dbus plugins), and tell me with a
> straight face that you would trust these modern-day desktop
> application writers with this interface.  Because they *will* find
> some interesting way to (ab)use it.....
> 
> Also, I didn't think the extra code complexity to implements timeouts
> was *that* bad --- it seemed fairly small for the functionality.

Just as an extra point of reference, VxFS supports a freeze/thaw by
ioctl very similar to this including a timeout in seconds. This
means someone else thought it was a useful feature.

http://sfdoccentral.symantec.com/sf/5.0/linux/manpages/vxfs/vxfsio_7.html

	Brad Boyer
	flar@...andria.com

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