linux-kernel - Re: document ext3 requirements

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Date:	Sun, 04 Jan 2009 01:08:14 +0100
From:	Martin MOKREJŠ <mmokrejs@...osome.natur.cuni.cz>
To:	Robert Hancock <hancockr@...w.ca>
CC:	Duane Griffin <duaneg@...da.com>, Pavel Machek <pavel@...e.cz>,
	kernel list <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>, tytso@....edu,
	mtk.manpages@...il.com, rdunlap@...otime.net,
	linux-doc@...r.kernel.org
Subject: Re: document ext3 requirements

Robert Hancock wrote:
> Martin MOKREJŠ wrote:
>> Duane Griffin wrote:
>>> 2009/1/3 Martin MOKREJŠ <mmokrejs@...osome.natur.cuni.cz>:
>>>> Hmm, so if my dual-boot machine does not shutdown correctly and I boot
>>>> accidentally in M$ Win where I use ext2 IFS driver and modify some
>>>> stuff on the ext3 drive, after a while reboot to linux and the journal
>>>> get re-played ... Mmm ...
>>> You *really* wouldn't want to be doing that.
>>>
>>> The other scenario that people have reported trouble with is
>>> suspending the system, booting a live CD which "read-only" mounts the
>>> filesystem (and replays the journal), then resuming.
>>
>> Why does not "mount -ro" die when it would have to replay the journal
>> with a message that user must run fsck.ext3 in order to be able to mount
>> it albeit read-only? Still I would prefer having an extra switch to
> 
> That would break typical system bootup in the unclean journal case,
> normally the root FS is mounted read-only to start with (which replays
> the journal) and remounted read-write later on - and usually the fsck
> utilities are located on the root filesystem..

Couldn't that be handled by e.g. openRC during boot, to provide the
say to be provided --force-journal-replay during "normal" boot?
Yes, that would mean e2fsprogs would become incompatible with older
versions but why not "fix" the logic?

> 
>> force mount RO while not touching the journal for disk forensics. I
>> think that would also prevent the cases when a LiveCD/rescue 
>> distribution would not mount+replay it automagically but user would
>> really have to provide the switch to the command. I am really not
>> using the recovery boot cd to touch my partitions in some cases
>> unwillingly.
>
> I agree, there should be a way to force it to mount "really read only"
> so it doesn't try to replay the journal. That might require just
> ignoring the journal content, which may result in the FS appearing
> corrupt, but for recovery/forensics purposes that seems better than
> nothing..

Fully agree.

M.

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