dm thin metadata: do not allow the data block size to change

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.

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

After:
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 <snitzer@redhat.com>
Acked-by: Joe Thornber <ejt@redhat.com>
Cc: stable@vger.kernel.org

diff --git a/drivers/md/dm-thin-metadata.c b/drivers/md/dm-thin-metadata.c
index b086a94..e9d33ad 100644 (file)
--- 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;