dm: prepare to support WRITE SAME

Allow targets to opt in to WRITE SAME support by setting
'num_write_same_requests' in the dm_target structure.

A dm device will only advertise WRITE SAME support if all its
targets and all its underlying devices support it.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index fa29557..6be58b6 100644 (file)
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1414,6 +1414,33 @@ static bool dm_table_all_devices_attribute(struct dm_table *t,
        return 1;
 }
 
+static int device_not_write_same_capable(struct dm_target *ti, struct dm_dev *dev,
+                                        sector_t start, sector_t len, void *data)
+{
+       struct request_queue *q = bdev_get_queue(dev->bdev);
+
+       return q && !q->limits.max_write_same_sectors;
+}
+
+static bool dm_table_supports_write_same(struct dm_table *t)
+{
+       struct dm_target *ti;
+       unsigned i = 0;
+
+       while (i < dm_table_get_num_targets(t)) {
+               ti = dm_table_get_target(t, i++);
+
+               if (!ti->num_write_same_requests)
+                       return false;
+
+               if (!ti->type->iterate_devices ||
+                   !ti->type->iterate_devices(ti, device_not_write_same_capable, NULL))
+                       return false;
+       }
+
+       return true;
+}
+
 void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
                               struct queue_limits *limits)
 {
@@ -1445,7 +1472,8 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
        else
                queue_flag_clear_unlocked(QUEUE_FLAG_NONROT, q);
 
-       q->limits.max_write_same_sectors = 0;
+       if (!dm_table_supports_write_same(t))
+               q->limits.max_write_same_sectors = 0;
 
        dm_table_set_integrity(t);
 

diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 38d27a1..d1f6cd8 100644 (file)
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -205,6 +205,11 @@ struct dm_target {
         */
        unsigned num_discard_requests;
 
+       /*
+        * The number of WRITE SAME requests that will be submitted to the target.
+        */
+       unsigned num_write_same_requests;
+
        /* target specific data */
        void *private;