linux-ext4 - Re: ext4_clear_journal_err: Filesystem error recorded from previous mount: IO failure

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Message-ID: <AANLkTim94HAvxTgvhdhmJ6oPR0YpaPT97TEXq8ZCfTPU@mail.gmail.com>
Date:	Sun, 24 Oct 2010 10:50:13 +0200
From:	Amir Goldstein <amir73il@...il.com>
To:	"Ted Ts'o" <tytso@....edu>
Cc:	Bernd Schubert <bs_lists@...ef.fastmail.fm>,
	linux-ext4@...r.kernel.org, Bernd Schubert <bschubert@....com>
Subject: Re: ext4_clear_journal_err: Filesystem error recorded from previous
 mount: IO failure

On Sun, Oct 24, 2010 at 12:17 AM, Ted Ts'o <tytso@....edu> wrote:
> On Sat, Oct 23, 2010 at 06:00:05PM +0200, Amir Goldstein wrote:
>>
>> IMHO, and I've said it before, the mount flag which Bernd requests
>> already exists, namely 'errors=', both as mount option and as
>> persistent default, but it is not enforced correctly on mount time.
>> If an administrator decides that the correct behavior when error is
>> detected is abort or remount-ro, what's the sense it letting the
>> filesystem mount read-write without fixing the problem?
>
> Again, consider the case of the root filesystem containing an error.
> When the error is first discovered during the source of the system's
> operation, and it's set to errors=panic, you want to immediately
> reboot the system.  But then, when root file system is mounted, it
> would be bad to have the system immediately panic again.  Instead,
> what you want to have happen is to allow e2fsck to run, correct the
> file system errors, and then system can go back to normal operation.
>
> So the current behavior was deliberately designed to be the way that
> it is, and the difference is between "what do you do when you come
> across a file system error", which is what the errors= mount option is
> all about, and "this file system has some kind of error associated
> with it".  Just because it has an error associated with it does not
> mean that immediately rebooting is the right thing to do, even if the
> file system is set to "errors=panic".  In fact, in the case of a root
> file system, it is manifestly the wrong thing to do.  If we did what
> you suggested, then the system would be trapped in a reboot loop
> forever.
>

Yes, I do realize that to panic on mount would be stupid :-)
this is why I wrote that there is no sense in mounting the file system
read-write.
let me rephrase the 3 error behaviors as the designer (you?) intended:
errors=continue - "always stay out of my way and let me corrupt my
file system as much as I want".
errors=read-only - "never let me corrupt my file system more than it
already is".
errors=panic - "never let me corrupt my file system ... and never let
me view files which may not be there after I reboot".

If you agree with my interpretations to the errors behavior codes,
than you should agree to enforcing on mount time:
errors=continue - if ERROR_FS, go a head and corrupt your file system
errors=read-only - if ERROR_FS, allow only read-only mount
errors=panic - if ERROR_FS, allow only read-only mount (files you see
now are safely stored on disk)

Amir.
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