[PATCH 1/4] block: provide plug based way of signaling forced no-wait semantics

[Jens Axboe <axboe@kernel.dk>]

Provide a way for the caller to specify that IO should be marked
with REQ_NOWAIT to avoid blocking on allocation, as well as a list
head for caller use.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 block/blk-core.c       | 6 ++++++
 include/linux/blkdev.h | 2 ++
 2 files changed, 8 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index 03252af8c82c..62a4904db921 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -958,6 +958,7 @@ generic_make_request_checks(struct bio *bio)
 	struct request_queue *q;
 	int nr_sectors = bio_sectors(bio);
 	blk_status_t status = BLK_STS_IOERR;
+	struct blk_plug *plug;
 	char b[BDEVNAME_SIZE];
 
 	might_sleep();
@@ -971,6 +972,10 @@ generic_make_request_checks(struct bio *bio)
 		goto end_io;
 	}
 
+	plug = blk_mq_plug(q, bio);
+	if (plug && plug->nowait)
+		bio->bi_opf |= REQ_NOWAIT;
+
 	/*
 	 * For a REQ_NOWAIT based request, return -EOPNOTSUPP
 	 * if queue is not a request based queue.
@@ -1800,6 +1805,7 @@ void blk_start_plug(struct blk_plug *plug)
 	INIT_LIST_HEAD(&plug->cb_list);
 	plug->rq_count = 0;
 	plug->multiple_queues = false;
+	plug->nowait = false;
 
 	/*
 	 * Store ordering should not be needed here, since a potential
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 8fd900998b4e..27887bf36d50 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1187,8 +1187,10 @@ extern void blk_set_queue_dying(struct request_queue *);
 struct blk_plug {
 	struct list_head mq_list; /* blk-mq requests */
 	struct list_head cb_list; /* md requires an unplug callback */
+	struct list_head nowait_list;	/* caller user */
 	unsigned short rq_count;
 	bool multiple_queues;
+	bool nowait;
 };
 #define BLK_MAX_REQUEST_COUNT 16
 #define BLK_PLUG_FLUSH_SIZE (128 * 1024)
-- 
2.27.0