[PATCH v16 07/26] block: Support block drivers that preserve the order of write requests

[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 related to
write serialization. 'driver_preserves_write_order' allows block drivers
to indicate that the order of write commands is preserved per hardware
queue and hence that serialization of writes per zone is not required if
all pending writes are submitted to the same hardware queue.

Cc: Damien Le Moal <dlemoal@kernel.org>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Nitesh Shetty <nj.shetty@samsung.com>
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   | 2 ++
 include/linux/blkdev.h | 5 +++++
 2 files changed, 7 insertions(+)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index f1d4dfdc37a7..329d8b65a8d7 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -633,6 +633,8 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 	}
 	t->max_secure_erase_sectors = min_not_zero(t->max_secure_erase_sectors,
 						   b->max_secure_erase_sectors);
+	t->driver_preserves_write_order = t->driver_preserves_write_order &&
+		b->driver_preserves_write_order;
 	t->zone_write_granularity = max(t->zone_write_granularity,
 					b->zone_write_granularity);
 	if (!(t->features & BLK_FEAT_ZONED)) {
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index a1fd0ddce5cf..72be33d02d1f 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -397,6 +397,11 @@ struct queue_limits {
 
 	unsigned int		max_open_zones;
 	unsigned int		max_active_zones;
+	/*
+	 * Whether or not the block driver preserves the order of write
+	 * requests. Set by the block driver.
+	 */
+	bool			driver_preserves_write_order;
 
 	/*
 	 * Drivers that set dma_alignment to less than 511 must be prepared to