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Date:	Fri,  8 Aug 2014 13:39:23 -0700
From:	Kamal Mostafa <>
Cc:	Mike Snitzer <>,
	Kamal Mostafa <>
Subject: [PATCH 3.13 140/259] dm thin metadata: do not allow the data block size to change -stable review patch.  If anyone has any objections, please let me know.


From: Mike Snitzer <>

commit 9aec8629ec829fc9403788cd959e05dd87988bd1 upstream.

The block size for the thin-pool's data device must remained fixed for
the life of the thin-pool.  Disallow any attempt to change the
thin-pool's data block size.

It should be noted that attempting to change the data block size via
thin-pool table reload will be ignored as a side-effect of the thin-pool
handover that the thin-pool target does during thin-pool table reload.

Here is an example outcome of attempting to load a thin-pool table that
reduced the thin-pool's data block size from 1024K to 512K.

kernel: device-mapper: thin: 253:4: growing the data device from 204800 to 409600 blocks

kernel: device-mapper: thin metadata: changing the data block size (from 2048 to 1024) is not supported
kernel: device-mapper: table: 253:4: thin-pool: Error creating metadata object
kernel: device-mapper: ioctl: error adding target to table

Signed-off-by: Mike Snitzer <>
Acked-by: Joe Thornber <>
Signed-off-by: Kamal Mostafa <>
 drivers/md/dm-thin-metadata.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/md/dm-thin-metadata.c b/drivers/md/dm-thin-metadata.c
index 07a6ea3..b63095c 100644
--- a/drivers/md/dm-thin-metadata.c
+++ b/drivers/md/dm-thin-metadata.c
@@ -613,6 +613,15 @@ static int __open_metadata(struct dm_pool_metadata *pmd)
 	disk_super = dm_block_data(sblock);
+	/* Verify the data block size hasn't changed */
+	if (le32_to_cpu(disk_super->data_block_size) != pmd->data_block_size) {
+		DMERR("changing the data block size (from %u to %llu) is not supported",
+		      le32_to_cpu(disk_super->data_block_size),
+		      (unsigned long long)pmd->data_block_size);
+		r = -EINVAL;
+		goto bad_unlock_sblock;
+	}
 	r = __check_incompat_features(disk_super, pmd);
 	if (r < 0)
 		goto bad_unlock_sblock;

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