linux-ext4 - Re: [PATCH] ext4: Use s_csum_seed instead of i_csum

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Message-ID: <20120709141248.GB3649@thunk.org>
Date:	Mon, 9 Jul 2012 10:12:48 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Tao Ma <tm@....ma>
Cc:	linux-ext4@...r.kernel.org, "Darrick J. Wong" <djwong@...ibm.com>
Subject: Re: [PATCH] ext4: Use s_csum_seed instead of i_csum_seed for xattr
 block csum.

On Sun, Jun 24, 2012 at 10:13:56PM +0800, Tao Ma wrote:
> From: Tao Ma <boyu.mt@...bao.com>
> 
> In xattr block operation, we use h_refcount to indicate whether the
> xattr block is shared among many inodes. And xattr block csum uses
> s_csum_seed if it is shared and i_csum_seed if it belongs to
> one inode. But this has a problem. So consider the block is shared
> first bewteen inode A and B, and B has some xattr update and CoW
> the xattr block. When it updates the *old* xattr block(because
> of the h_refcount change) and calls ext4_xattr_release_block, we
> has no idea that inode A is the real owner of the *old* xattr
> block and we can't use the i_csum_seed of inode A either in xattr
> block csum calculation. And I don't think we have an easy way to
> find inode A.
> 
> So this patch just removes the tricky i_csum_seed and we now uses
> s_csum_seed every time for the xattr block csum. The corresponding
> patch for the e2fsprogs will be sent in another patch.
> 
> This is spotted by xfstests 117.
> 
> Cc: Darrick J. Wong <djwong@...ibm.com>
> Cc: "Theodore Ts'o" <tytso@....edu>
> Signed-off-by: Tao Ma <boyu.mt@...bao.com>

Thanks, applied.

					- Ted
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