md/raid5: prepare for allowing reshape to change chunksize.

Add "prev_chunk" to raid5_conf_t, similar to "previous_raid_disks", to
remember what the chunk size was before the reshape that is currently
underway.

This seems like duplication with "chunk_size" and "new_chunk" in
mddev_t, and to some extent it is, but there are differences.
The values in mddev_t are always defined and often the same.
The prev* values are only defined if a reshape is underway.

Also (and more significantly) the raid5_conf_t values will be changed
at the same time (inside an appropriate lock) that the reshape is
started by setting reshape_position.  In contrast, the new_chunk value
is set when the sysfs file is written which could be well before the
reshape starts.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index a081fb40a5a2..b9c93280fc1d 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -350,6 +350,7 @@ struct raid5_private_data {
          */
         sector_t                reshape_safe;
         int                     previous_raid_disks;
+        int                     prev_chunk;
         short                   generation; /* increments with every reshape */
 
         struct list_head        handle_list; /* stripes needing handling */