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Re: [PATCH 1/3] xfs: xfs_swap_extents needs to handle dynamic fork offse

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 1/3] xfs: xfs_swap_extents needs to handle dynamic fork offsets
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Thu, 14 Jan 2010 01:42:55 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <1263432836-13368-2-git-send-email-david@xxxxxxxxxxxxx>
References: <1263432836-13368-1-git-send-email-david@xxxxxxxxxxxxx> <1263432836-13368-2-git-send-email-david@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.19 (2009-01-05)
On Thu, Jan 14, 2010 at 12:33:54PM +1100, Dave Chinner wrote:
> When swapping extents, we can corrupt inodes by swapping data forks
> that are in incompatible formats.  This is caused by the two indoes
> having different fork offsets due to the presence of an attribute
> fork on an attr2 filesystem.  xfs_fsr tries to be smart about
> setting the fork offset, but the trick it plays only works on attr1
> (old fixed format attribute fork) filesystems.
> Changing the way xfs_fsr sets up the attribute fork will prevent
> this situation from ever occurring, so in the kernel code we can get
> by with a preventative fix - check that the data fork in the
> defragmented inode is in a format valid for the inode it is being
> swapped into.  This will lead to files that will silently and
> potentially repeatedly fail defragmentation, so issue a warning to
> the log when this particular failure occurs to let us know that
> xfs_fsr needs updating/fixing.
> To help identify how to improve xfs_fsr to avoid this issue, add
> trace points for the inodes being swapped so that we can determine
> why the swap was rejected and to confirm that the code is making the
> right decisions and modifications when swapping forks.
> A further complication is even when the swap is allowed to proceed
> when the fork offset is different between the two inodes then value
> for the maximum number of extents the data fork can hold can be
> wrong. Make sure these are also set correctly after the swap occurs.
> Signed-off-by: Dave Chinner <david@xxxxxxxxxxxxx>
> ---
>  fs/xfs/xfs_dfrag.c |  106 
> ++++++++++++++++++++++++++++++++++++++++++++--------

Looks good,

Reviewed-by: Christoph Hellwig <hch@xxxxxx>

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