block: Introduce blk_set_stacking_limits function

Stacking driver queue limits are typically bounded exclusively by the
capabilities of the low level devices, not by the stacking driver
itself.

This patch introduces blk_set_stacking_limits() which has more liberal
metrics than the default queue limits function. This allows us to
inherit topology parameters from bottom devices without manually
tweaking the default limits in each driver prior to calling the stacking
function.

Since there is now a clear distinction between stacking and low-level
devices, blk_set_default_limits() has been modified to carry the more
conservative values that we used to manually set in
blk_queue_make_request().

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

2 files changed, 4 insertions, 3 deletions

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 8e9132130142..63cc54289aff 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -699,7 +699,7 @@ static int validate_hardware_logical_block_alignment(struct dm_table *table,
         while (i < dm_table_get_num_targets(table)) {
                 ti = dm_table_get_target(table, i++);
 
-                blk_set_default_limits(&ti_limits);
+                blk_set_stacking_limits(&ti_limits);
 
                 /* combine all target devices' limits */
                 if (ti->type->iterate_devices)
@@ -1221,10 +1221,10 @@ int dm_calculate_queue_limits(struct dm_table *table,
         struct queue_limits ti_limits;
         unsigned i = 0;
 
-        blk_set_default_limits(limits);
+        blk_set_stacking_limits(limits);
 
         while (i < dm_table_get_num_targets(table)) {
-                blk_set_default_limits(&ti_limits);
+                blk_set_stacking_limits(&ti_limits);
 
                 ti = dm_table_get_target(table, i++);
 
diff --git a/drivers/md/md.c b/drivers/md/md.c
index ee981737edfc..114ba155af87 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4622,6 +4622,7 @@ static int md_alloc(dev_t dev, char *name)
         mddev->queue->queuedata = mddev;
 
         blk_queue_make_request(mddev->queue, md_make_request);
+        blk_set_stacking_limits(&mddev->queue->limits);
 
         disk = alloc_disk(1 << shift);
         if (!disk) {