linux-ext4 - Re: xt4 - True Readonly mount [WAS - Re: [Bug 14354] Bad corruption with 2.6.32-rc1 and upwards]

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Date:	Fri, 30 Oct 2009 10:14:56 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Greg Freemyer <greg.freemyer@...il.com>
CC:	Ted Augustine <taugustine@...hpathways.com>,
	Alexey Fisher <bug-track@...her-privat.net>,
	linux-ext4@...r.kernel.org
Subject: Re: xt4 - True Readonly mount [WAS - Re: [Bug 14354] Bad corruption
 with 	2.6.32-rc1 and upwards]

Greg Freemyer wrote:
> On Fri, Oct 30, 2009 at 4:22 AM,  <bugzilla-daemon@...zilla.kernel.org> wrote:
>> http://bugzilla.kernel.org/show_bug.cgi?id=14354
>>
>> --- Comment #152 from Alexey Fisher <bug-track@...her-privat.net>  2009-10-30 08:22:10 ---
>> Ted,
>> Thank you for explanation :)
>> Notice: i learning computer forensic, and was trained to mount all evidence
>> systems with "-o ro" to not contaminate it. It seems like ext4 break this
>> tradition, so many forensics will surprised  why md5sum do not match.
> 
> Ted,  (Alexey there is a response to further down).
> 
> I have not followed this thread ultra-closely but Alexey's comment got
> my attention.
> 
> Ignoring computer forensics, with LVM snapshots, hardware raid array
> snapshots, etc. even in the presence of a dirty log, we need to be
> able to mount a drive in true read-only fashion fro many backup
> operations to function correctly.
> 
> XFS added an extra mount flag for that 5 or so years ago.
> I hope ext4 either has or will add a true read-only mount option.
> Maybe Eric Sandeen remembers the actual drivers for adding that
> feature to XFS.
> 

After a little brief digging I'm not sure when the xfs mount option went 
in or why...

But for both

xfs: mount -o ro,norecovery

and

ext[34]: mount -o ro,noload

I don't think either one should touch the disk.

Also, both should skip journal replay if you set the block device 
readonly prior to mount (hdparm -r can do this).

-Eric
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