block: Support block drivers that preserve the order of write requests

Some storage controllers preserve the request order per hardware queue.
Some but not all device mapper drivers preserve the bio order. Introduce
the request queue limit member variable 'driver_preserves_write_order' to
allow block drivers and device mapper 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 <[email protected]>
Cc: Hannes Reinecke <[email protected]>
Cc: Nitesh Shetty <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Ming Lei <[email protected]>
Signed-off-by: Bart Van Assche <[email protected]>

Author: bvanassche

block/blk-settings.c

@@ -814,6 +814,8 @@ 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)) {

include/linux/blkdev.h

@@ -413,6 +413,11 @@ 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 per hardware queue. Set by the block driver.
+	 */
+	bool			driver_preserves_write_order;
 
 	/*
 	 * Drivers that set dma_alignment to less than 511 must be prepared to