linux-kernel - Re: document ext3 requirements

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Date:	Sun, 4 Jan 2009 21:22:35 -0600
From:	Rob Landley <rob@...dley.net>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Theodore Tso <tytso@....edu>, Duane Griffin <duaneg@...da.com>,
	Valdis.Kletnieks@...edu,
	Martin MOKREJŠ <mmokrejs@...osome.natur.cuni.cz>,
	Pavel Machek <pavel@...e.cz>,
	kernel list <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>, mtk.manpages@...il.com,
	rdunlap@...otime.net, linux-doc@...r.kernel.org
Subject: Re: document ext3 requirements

On Sunday 04 January 2009 13:21:06 Geert Uytterhoeven wrote:
> I think most people get shocked when they discover that mounting something
> read-only may actualy write to the media. This is a bit unexpected (hey, if
> I mount `read-only', I expect that no writes will happen), as it behaved
> differently before the introduction of journalling.

Is this an unreasonable use case:

  kill -STOP $(pidof qemu)
  mount -o loop,ro hdb.img blah
  cp blah/thingy thingy
  umount blah
  kill -CONT $(pidof qemu)

Currently, if your loopback mount is -t ext3 it'll write to the block device, 
and if your mount is -t ext2 it'll refuse to work on an unclean ext3 
filesystem, even if it's read only.  (But it _will_ work on an unclean ext2 
filesystem.)

My theory when I first found out about this was "the filesystem developers 
hate me personally".

Rob
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