From: Theodore Tso <tytso@mit.edu>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andi Kleen <andi@firstfloor.org>,
Kyle Moffett <kyle@moffetthome.net>,
Alan Cox <alan@lxorguk.ukuu.org.uk>,
Zachary Amsden <zamsden@redhat.com>, Tejun Heo <tj@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, axboe@kernel.dk, hch@infradead.org,
akpm@linux-foundation.org, Paul.Clements@steeleye.com,
miklos <miklos@szeredi.hu>
Subject: Re: [PATCH] Allow userspace block device implementation
Date: Tue, 28 Jul 2009 18:56:35 -0400 [thread overview]
Message-ID: <20090728225635.GK31679@mit.edu> (raw)
In-Reply-To: <alpine.LFD.2.01.0907281333490.3186@localhost.localdomain>
On Tue, Jul 28, 2009 at 01:50:56PM -0700, Linus Torvalds wrote:
>
> Filesystems long ago _used_ to index things by device number and block -
> and that meant that re-reading partition tables was _really_ dangerous,
> because the "device number" would just magically mean something else for a
> mounted filesystem. But we've indexed things by bdev for a longish time
> now, and most (all?) filesystems use "sb_bread()" instead of bread etc.
Filesystems don't, but some userspace programs do depend on the dev_t
returned by stat to uniquely identify a mounted filesystem. (And it's
guaranteed by POSIX). So what this means is that if we're going to
allow re-reading the partition table, we should (a) avoid changing the
dev_t used by any mounted filesystem, and (b) we should either assign
a new dev_t for any new partitions, or we should disallow mounting a
filesystem with a new dev_t already in use by an already mounted
filesystem with the same dev_t before the partition table was
reorganized.
- Ted
next prev parent reply other threads:[~2009-07-28 22:57 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-27 9:57 [PATCH] Allow userspace block device implementation Zachary Amsden
2009-07-27 12:56 ` Peter Zijlstra
2009-07-27 13:25 ` Alan Cox
2009-07-27 19:46 ` Zachary Amsden
2009-07-27 20:24 ` Peter Zijlstra
2009-07-27 21:02 ` Alan Cox
2009-07-28 1:21 ` Tejun Heo
2009-07-28 3:53 ` Zachary Amsden
2009-07-28 10:27 ` Alan Cox
2009-07-28 16:00 ` Linus Torvalds
2009-07-28 18:36 ` Kyle Moffett
2009-07-28 18:51 ` Linus Torvalds
2009-07-28 19:07 ` Alan Cox
2009-07-28 19:49 ` Andi Kleen
2009-07-28 20:50 ` Linus Torvalds
2009-07-28 21:09 ` Andi Kleen
2009-07-28 22:56 ` Theodore Tso [this message]
2009-08-07 18:08 ` Pavel Machek
2009-08-10 22:47 ` Zachary Amsden
-- strict thread matches above, loose matches on Subject: below --
2009-07-28 20:37 devzero
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