[PATCH v8 1/9] block: Introduce more member variables related to zone write locking

[Bart Van Assche <bvanassche@acm.org>]

Many but not all storage controllers require serialization of zoned writes.
Introduce a new request queue limit member variable
(driver_preserves_write_order) that allows block drivers to indicate that
the order of write commands is preserved and hence that serialization of
writes per zone is not required.

Make disk_set_zoned() set 'use_zone_write_lock' only if the block device
has zones and if the block driver does not preserve the order of write
requests.

Cc: Damien Le Moal <dlemoal@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 block/blk-settings.c   |  7 +++++++
 include/linux/blkdev.h | 10 ++++++++++
 2 files changed, 17 insertions(+)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 0046b447268f..3a7748af1bef 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -56,6 +56,8 @@ void blk_set_default_limits(struct queue_limits *lim)
 	lim->alignment_offset = 0;
 	lim->io_opt = 0;
 	lim->misaligned = 0;
+	lim->driver_preserves_write_order = false;
+	lim->use_zone_write_lock = false;
 	lim->zoned = BLK_ZONED_NONE;
 	lim->zone_write_granularity = 0;
 	lim->dma_alignment = 511;
@@ -685,6 +687,9 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 						   b->max_secure_erase_sectors);
 	t->zone_write_granularity = max(t->zone_write_granularity,
 					b->zone_write_granularity);
+	/* Request-based stacking drivers do not reorder requests. */
+	t->driver_preserves_write_order = b->driver_preserves_write_order;
+	t->use_zone_write_lock = b->use_zone_write_lock;
 	t->zoned = max(t->zoned, b->zoned);
 	return ret;
 }
@@ -949,6 +954,8 @@ void disk_set_zoned(struct gendisk *disk, enum blk_zoned_model model)
 	}
 
 	q->limits.zoned = model;
+	q->limits.use_zone_write_lock = model != BLK_ZONED_NONE &&
+		!q->limits.driver_preserves_write_order;
 	if (model != BLK_ZONED_NONE) {
 		/*
 		 * Set the zone write granularity to the device logical block
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 2f5371b8482c..2c090a28ec78 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -316,6 +316,16 @@ struct queue_limits {
 	unsigned char		misaligned;
 	unsigned char		discard_misaligned;
 	unsigned char		raid_partial_stripes_expensive;
+	/*
+	 * Whether or not the block driver preserves the order of write
+	 * requests. Set by the block driver.
+	 */
+	bool			driver_preserves_write_order;
+	/*
+	 * Whether or not zone write locking should be used. Set by
+	 * disk_set_zoned().
+	 */
+	bool			use_zone_write_lock;
 	enum blk_zoned_model	zoned;
 
 	/*