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Re: [PATCH 3/3] Add timeout feature

To: Theodore Tso <tytso@xxxxxxx>, Pavel Machek <pavel@xxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Takashi Sato <t-sato@xxxxxxxxxxxxx>, akpm@xxxxxxxxxxxxxxxxxxxx, viro@xxxxxxxxxxxxxxxxxx, "linux-ext4@xxxxxxxxxxxxxxx" <linux-ext4@xxxxxxxxxxxxxxx>, "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>, "dm-devel@xxxxxxxxxx" <dm-devel@xxxxxxxxxx>, "linux-fsdevel@xxxxxxxxxxxxxxx" <linux-fsdevel@xxxxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, axboe@xxxxxxxxx, mtk.manpages@xxxxxxxxxxxxxx
Subject: Re: [PATCH 3/3] Add timeout feature
From: Brad Boyer <flar@xxxxxxxxxxxxx>
Date: Tue, 8 Jul 2008 21:21:47 -0700
In-reply-to: <20080709010922.GE9957@xxxxxxx>
References: <20080630212450t-sato@xxxxxxxxxxxxxxx> <20080701081026.GB16691@xxxxxxxxxxxxx> <20080707110730.GG5643@xxxxxx> <20080708231026.GP11558@disturbed> <20080708232031.GE18195@xxxxxxxxxx> <20080709005254.GQ11558@disturbed> <20080709010922.GE9957@xxxxxxx>
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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.


        Brad Boyer

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