md/raid5: change reshape-progress measurement to cope with reshaping backwards.

When reducing the number of devices in a raid4/5/6, the reshape
process has to start at the end of the array and work down to the
beginning.  So we need to handle expand_progress and expand_lo
differently.

This patch renames "expand_progress" and "expand_lo" to avoid the
implication that anything is getting bigger (expand->reshape) and
every place they are used, we make sure that they are used the right
way depending on whether delta_disks is positive or negative.

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

1 files changed, 10 insertions, 5 deletions

diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index c2f37f25ef44..b2edcc434e41 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -337,11 +337,16 @@ struct raid5_private_data {
         int                     raid_disks;
         int                     max_nr_stripes;
 
-        /* used during an expand */
-        sector_t                expand_progress;        /* MaxSector when no expand happening */
-        sector_t                expand_lo; /* from here up to expand_progress it out-of-bounds
-                                            * as we haven't flushed the metadata yet
-                                            */
+        /* reshape_progress is the leading edge of a 'reshape'
+         * It has value MaxSector when no reshape is happening
+         * If delta_disks < 0, it is the last sector we started work on,
+         * else is it the next sector to work on.
+         */
+        sector_t                reshape_progress;
+        /* reshape_safe is the trailing edge of a reshape.  We know that
+         * before (or after) this address, all reshape has completed.
+         */
+        sector_t                reshape_safe;
         int                     previous_raid_disks;
 
         struct list_head        handle_list; /* stripes needing handling */