linux-kernel - [PATCH 3.16.y-ckt 070/180] libxfs: pack the agfl header structure so XFS_AGFL

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Message-Id: <1454538786-12215-71-git-send-email-luis.henriques@canonical.com>
Date:	Wed,  3 Feb 2016 22:31:16 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	"Darrick J . Wong" <darrick.wong@...cle.com>,
	Dave Chinner <david@...morbit.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 070/180] libxfs: pack the agfl header structure so XFS_AGFL_SIZE is correct

3.16.7-ckt24 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: "Darrick J. Wong" <darrick.wong@...cle.com>

commit 96f859d52bcb1c6ea6f3388d39862bf7143e2f30 upstream.

Because struct xfs_agfl is 36 bytes long and has a 64-bit integer
inside it, gcc will quietly round the structure size up to the nearest
64 bits -- in this case, 40 bytes.  This results in the XFS_AGFL_SIZE
macro returning incorrect results for v5 filesystems on 64-bit
machines (118 items instead of 119).  As a result, a 32-bit xfs_repair
will see garbage in AGFL item 119 and complain.

Therefore, tell gcc not to pad the structure so that the AGFL size
calculation is correct.

Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
Reviewed-by: Dave Chinner <dchinner@...hat.com>
Signed-off-by: Dave Chinner <david@...morbit.com>
[ luis: backported to 3.16:
  - file rename: fs/xfs/libxfs/xfs_format.h -> fs/xfs/xfs_ag.h ]
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 fs/xfs/xfs_ag.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_ag.h b/fs/xfs/xfs_ag.h
index 6e247a99f5db..5899b64f5786 100644
--- a/fs/xfs/xfs_ag.h
+++ b/fs/xfs/xfs_ag.h
@@ -232,7 +232,7 @@ typedef struct xfs_agfl {
 	__be64		agfl_lsn;
 	__be32		agfl_crc;
 	__be32		agfl_bno[];	/* actually XFS_AGFL_SIZE(mp) */
-} xfs_agfl_t;
+} __attribute__((packed)) xfs_agfl_t;

 #define XFS_AGFL_CRC_OFF	offsetof(struct xfs_agfl, agfl_crc)