linux-ext4 - Re: [RFC] [PATCH] Flex_BG ialloc awareness V2.

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Message-ID: <20071214170106.GQ3214@webber.adilger.int>
Date:	Fri, 14 Dec 2007 10:01:06 -0700
From:	Andreas Dilger <adilger@....com>
To:	"Jose R. Santos" <jrs@...ibm.com>
Cc:	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [RFC] [PATCH] Flex_BG ialloc awareness V2.

On Dec 13, 2007  20:36 -0600, Jose R. Santos wrote:
> ... if the value in the super block is corrupted and
> does not represent the actual flexbg size, the inode allocation will
> behave in weird unexpected ways.  Just as we check that the bitmaps are
> within the block group range (when not using flexbg), we should
> probably sanity check the size of the flexbg as reported in the super
> block.
> 
> Or do you believe the check is unnecessary?

Well, I can imagine in some cases that the flexbg will not be completely
contiguous on disk (e.g. after a filesystem resize, if there are bad
blocks, etc).  As long as the group descriptors themselves are correct
(i.e. referencing valid bitmaps/itable) then it shouldn't cause a mount
failure if the per-group data isn't strictly aligned according to the
superblock flexbg count.

We would need to validate the group descriptor separately though (e.g.
group checksums).

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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