dm integrity: fix excessive alignment of metadata runs

Metadata runs are supposed to be aligned on 4k boundary (so that they work
efficiently with disks with 4k sectors). However, there was a programming
bug that makes them aligned on 128k boundary instead. The unused space is
wasted.

Fix this bug by providing a proper 4k alignment. In order to keep
existing volumes working, we introduce a new flag SB_FLAG_FIXED_PADDING
- when the flag is clear, we calculate the padding the old way. In order
to make sure that the old version cannot mount the volume created by the
new version, we increase superblock version to 4.

Also in order to not break with old integritysetup, we fix alignment
only if the parameter "fix_padding" is present when formatting the
device.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/Documentation/admin-guide/device-mapper/dm-integrity.rst b/Documentation/admin-guide/device-mapper/dm-integrity.rst
index a30aa91b5fbe..594095b54b29 100644
--- a/Documentation/admin-guide/device-mapper/dm-integrity.rst
+++ b/Documentation/admin-guide/device-mapper/dm-integrity.rst
@@ -177,6 +177,11 @@ bitmap_flush_interval:number
 	The bitmap flush interval in milliseconds. The metadata buffers
 	are synchronized when this interval expires.
 
+fix_padding
+	Use a smaller padding of the tag area that is more
+	space-efficient. If this option is not present, large padding is
+	used - that is for compatibility with older kernels.
+
 
 The journal mode (D/J), buffer_sectors, journal_watermark, commit_time can
 be changed when reloading the target (load an inactive table and swap the