linux-kernel - Re: document ext3 requirements

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Message-ID: <20090104193637.GB22958@mit.edu>
Date:	Sun, 4 Jan 2009 14:36:37 -0500
From:	Theodore Tso <tytso@....edu>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	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 Sun, Jan 04, 2009 at 08:21:06PM +0100, Geert Uytterhoeven wrote:
> As mentioned before, suspending a laptop (running from hdd), running
> a live CD, and expecting everything to work fine when resuming from
> hdd?
> 
> 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.

It's been this way for about a decade....  that being said, if you
really want to do this, you can today via "mount -o ro,noload /dev/XXX
/mntpt".  However, the system could crash or fail because the
filesystem without having run the journal could be quite inconsistent.  

> As for mounting the root file system read-only during early boot up, and
> remounting it read-write later, I guess it's quite complicated to replay the
> journal (in RAM) on read-only mount, and deferring the replay writeback until
> remounting read-write?

It's not *that* hard; if someone would like to cons up a patch, please
feel free....  but it's certainly not a high priority for me or most
of the other ext3 filesystem developers.

					- Ted
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