linux-kernel - Re: document ext3 requirements

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Message-ID: <e9e943910901031641x4c900b6ar5d0f50b648584b7b@mail.gmail.com>
Date:	Sun, 4 Jan 2009 00:41:51 +0000
From:	"Duane Griffin" <duaneg@...da.com>
To:	"Martin MOKREJŠ" 
	<mmokrejs@...osome.natur.cuni.cz>
Cc:	"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

2009/1/4 Martin MOKREJŠ <mmokrejs@...osome.natur.cuni.cz>:
> Duane Griffin wrote:
>> 2009/1/3 Martin MOKREJŠ <mmokrejs@...osome.natur.cuni.cz>:
>>> 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
>>> 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.
>>
>> Well, that would make things rather tricky. As in, shutting down
>> uncleanly would render your system unbootable.
>
> ??? If I am booted off a CD/DVD drive I just do not want my system
> to be touched. I am fine if the dist mounts my drives automagically
> in read-only mode but if that currently forces journal replay then no,
> thanks. ;)

I agree, it isn't a great situation. Nonetheless, it has always been
thus for ext3, and so far we've muddled along. Unless and until we can
replay the journal in-memory without touching the on-disk data, we are
stuck with it.

We can't refuse to mount an unclean FS, as that would break booting.
We also can't ignore the journal by default, if/when we get a patch to
do so at all, as that effectively corrupts random chunks of the FS.
Fine for forensics and recovery; not so much for booting from.

> M.

Cheers,
Duane.

-- 
"I never could learn to drink that blood and call it wine" - Bob Dylan
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