[PATCH v6 1/7] block: Introduce the flag QUEUE_FLAG_NO_ZONE_WRITE_LOCK

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

Writes in sequential write required zones must happen at the write
pointer. Even if the submitter of the write commands (e.g. a filesystem)
submits writes for sequential write required zones in order, the block
layer or the storage controller may reorder these write commands.

The zone locking mechanism in the mq-deadline I/O scheduler serializes
write commands for sequential zones. Some but not all storage controllers
require this serialization. Introduce a new request queue flag to allow
block drivers to indicate that they preserve the order of write commands
and thus do not require serialization of writes per zone.

Reviewed-by: 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>
---
 include/linux/blkdev.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 2f5371b8482c..b6eb988f81f3 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -534,6 +534,12 @@ struct request_queue {
 #define QUEUE_FLAG_NONROT	6	/* non-rotational device (SSD) */
 #define QUEUE_FLAG_VIRT		QUEUE_FLAG_NONROT /* paravirt device */
 #define QUEUE_FLAG_IO_STAT	7	/* do disk/partitions IO accounting */
+/*
+ * The device supports not using the zone write locking mechanism to serialize
+ * write operations (REQ_OP_WRITE, REQ_OP_WRITE_ZEROES) issued to a sequential
+ * write required zone (BLK_ZONE_TYPE_SEQWRITE_REQ).
+ */
+#define QUEUE_FLAG_NO_ZONE_WRITE_LOCK 8
 #define QUEUE_FLAG_NOXMERGES	9	/* No extended merges */
 #define QUEUE_FLAG_ADD_RANDOM	10	/* Contributes to random pool */
 #define QUEUE_FLAG_SYNCHRONOUS	11	/* always completes in submit context */
@@ -597,6 +603,11 @@ bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q);
 #define blk_queue_skip_tagset_quiesce(q) \
 	test_bit(QUEUE_FLAG_SKIP_TAGSET_QUIESCE, &(q)->queue_flags)
 
+static inline bool blk_queue_no_zone_write_lock(struct request_queue *q)
+{
+	return test_bit(QUEUE_FLAG_NO_ZONE_WRITE_LOCK, &q->queue_flags);
+}
+
 extern void blk_set_pm_only(struct request_queue *q);
 extern void blk_clear_pm_only(struct request_queue *q);