[PATCH v4 11/28] block: Allow BIO-based drivers to use blk_revalidate_disk_zones()

[Damien Le Moal]

In preparation for allowing BIO based device drivers to use zone write
plugging and its zone append emulation, allow these drivers to call
blk_revalidate_disk_zones() so that all zone resources necessary to zone
write plugging can be initialized.

To do so, remove the check in blk_revalidate_disk_zones() restricting
the use of this function to mq request-based drivers to allow also
BIO-based drivers to use it. This is safe to do as long as the
BIO-based block device queue is already setup and usable, as it should,
and can be safely frozen.

The helper function disk_need_zone_resources() is added to control the
allocation and initialization of the zone write plug hash table and
of the conventional zone bitmap only for mq devices and for BIO-based
devices that require zone append emulation.

Signed-off-by: Damien Le Moal <dlemoal at kernel.org>
Reviewed-by: Christoph Hellwig <hch at lst.de>
---
 block/blk-zoned.c | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/block/blk-zoned.c b/block/blk-zoned.c
index 71d692d9d851..c60d5f074585 100644
--- a/block/blk-zoned.c
+++ b/block/blk-zoned.c
@@ -1527,12 +1527,28 @@ void disk_free_zone_resources(struct gendisk *disk)
 	disk->nr_zones = 0;
 }
 
+static inline bool disk_need_zone_resources(struct gendisk *disk)
+{
+	/*
+	 * All mq zoned devices need zone resources so that the block layer
+	 * can automatically handle write BIO plugging. BIO-based device drivers
+	 * (e.g. DM devices) are normally responsible for handling zone write
+	 * ordering and do not need zone resources, unless the driver requires
+	 * zone append emulation.
+	 */
+	return queue_is_mq(disk->queue) ||
+		queue_emulates_zone_append(disk->queue);
+}
+
 static int disk_revalidate_zone_resources(struct gendisk *disk,
 					  unsigned int nr_zones)
 {
 	struct queue_limits *lim = &disk->queue->limits;
 	unsigned int pool_size;
 
+	if (!disk_need_zone_resources(disk))
+		return 0;
+
 	/*
 	 * If the device has no limit on the maximum number of open and active
 	 * zones, use BLK_ZONE_WPLUG_DEFAULT_POOL_SIZE.
@@ -1650,6 +1666,9 @@ static int blk_revalidate_zone_cb(struct blk_zone *zone, unsigned int idx,
 				disk->disk_name);
 			return -ENODEV;
 		}
+
+		if (!disk_need_zone_resources(disk))
+			break;
 		if (!args->conv_zones_bitmap) {
 			args->conv_zones_bitmap =
 				blk_alloc_zone_bitmap(q->node, args->nr_zones);
@@ -1681,10 +1700,11 @@ static int blk_revalidate_zone_cb(struct blk_zone *zone, unsigned int idx,
 		/*
 		 * We need to track the write pointer of all zones that are not
 		 * empty nor full. So make sure we have a zone write plug for
-		 * such zone.
+		 * such zone if the device has a zone write plug hash table.
 		 */
 		wp_offset = blk_zone_wp_offset(zone);
-		if (wp_offset && wp_offset < zone_sectors) {
+		if (disk->zone_wplugs_hash &&
+		    wp_offset && wp_offset < zone_sectors) {
 			zwplug = disk_get_and_lock_zone_wplug(disk, zone->start,
 							      GFP_NOIO, &flags);
 			if (!zwplug)
@@ -1715,8 +1735,8 @@ static int blk_revalidate_zone_cb(struct blk_zone *zone, unsigned int idx,
  * be called within the disk ->revalidate method for blk-mq based drivers.
  * Before calling this function, the device driver must already have set the
  * device zone size (chunk_sector limit) and the max zone append limit.
- * For BIO based drivers, this function cannot be used. BIO based device drivers
- * only need to set disk->nr_zones so that the sysfs exposed value is correct.
+ * BIO based drivers can also use this function as long as the device queue
+ * can be safely frozen.
  * If the @update_driver_data callback function is not NULL, the callback is
  * executed with the device request queue frozen after all zones have been
  * checked.
@@ -1733,8 +1753,6 @@ int blk_revalidate_disk_zones(struct gendisk *disk,
 
 	if (WARN_ON_ONCE(!blk_queue_is_zoned(q)))
 		return -EIO;
-	if (WARN_ON_ONCE(!queue_is_mq(q)))
-		return -EIO;
 
 	if (!capacity)
 		return -ENODEV;
-- 
2.44.0