[PATCH V6 11/12] block: allow to control FLAG_POLL via sysfs for bio poll capable queue

[Ming Lei <ming.lei@redhat.com>]

Prepare for supporting bio based io polling. If one disk is capable of
bio polling, we allow user to control FLAG_POLL via sysfs.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-sysfs.c     | 14 ++++++++++++--
 include/linux/genhd.h |  2 ++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index fed4981b1f7a..3620db390658 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -430,9 +430,14 @@ static ssize_t queue_poll_store(struct request_queue *q, const char *page,
 {
 	unsigned long poll_on;
 	ssize_t ret;
+	struct gendisk *disk = queue_to_disk(q);
 
-	if (!q->tag_set || q->tag_set->nr_maps <= HCTX_TYPE_POLL ||
-	    !q->tag_set->map[HCTX_TYPE_POLL].nr_queues)
+	if (!queue_is_mq(q) && !(disk->flags & GENHD_FL_CAP_BIO_POLL))
+		return -EINVAL;
+
+	if (queue_is_mq(q) && (!q->tag_set ||
+	    q->tag_set->nr_maps <= HCTX_TYPE_POLL ||
+	    !q->tag_set->map[HCTX_TYPE_POLL].nr_queues))
 		return -EINVAL;
 
 	ret = queue_var_store(&poll_on, page, count);
@@ -442,6 +447,11 @@ static ssize_t queue_poll_store(struct request_queue *q, const char *page,
 	if (poll_on) {
 		blk_queue_flag_set(QUEUE_FLAG_POLL, q);
 	} else {
+		/*
+		 * For bio queue, it is safe to just freeze bio submission
+		 * activity because we don't read FLAG_POLL after bio is
+		 * submitted.
+		 */
 		blk_mq_freeze_queue(q);
 		blk_queue_flag_clear(QUEUE_FLAG_POLL, q);
 		blk_mq_unfreeze_queue(q);
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 7e9660ea967d..e5ae77cba853 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -104,6 +104,8 @@ struct partition_meta_info {
 #define GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE	0x0100
 #define GENHD_FL_NO_PART_SCAN			0x0200
 #define GENHD_FL_HIDDEN				0x0400
+/* only valid for bio based disk */
+#define GENHD_FL_CAP_BIO_POLL			0x0800
 
 enum {
 	DISK_EVENT_MEDIA_CHANGE			= 1 << 0, /* media changed */
-- 
2.29.2