linux-kernel - Re: Add a norecovery option to ext3/4?

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Message-ID: <20070409033134.GB13980@implementation>
Date:	Mon, 9 Apr 2007 05:31:34 +0200
From:	Samuel Thibault <samuel.thibault@...-lyon.org>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Add a norecovery option to ext3/4?

Eric Sandeen, le Sun 08 Apr 2007 22:24:50 -0500, a écrit :
> Samuel Thibault wrote:
> >Distribution installers usually try to probe OSes for building a suited
> >grub menu.  Unfortunately, mounting an ext3 partition, even in read-only
> >mode, does perform some operations on the filesystem (log recovery).
> >This is not a good idea since it may silently garbage data.  
> 
> Can you elaborate?  Under what circumstances is log replay going to harm 
> data?  Do you mean that the installer mounts partitions, looking for 
> what OS is installed?  How is that harmful?
> 
> Ohhh... this is http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=417407 
> isn't it?

Yes.

> Hm, so the root cause there seems that the installer found 2 legs of a 
> mirror and mounted them independently, recovering them independently... 
> But why did that cause problems?

Because that thrashed his data (or at least it didn't help to keep data
safe).

> Other options you may have in the installer, though, is to check for
> md superblocks before mounting bare partitions, or maybe use the
> BLKROSET ioctl to set the block device to read-only prior to mount,
> for added insurance...

That's one the things proposed in the bugreport yes.

Samuel
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