block: provide plug based way of signaling forced no-wait semantics

Provide a way for the caller to specify that IO should be marked
with REQ_NOWAIT to avoid blocking on allocation.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-core.c b/block/blk-core.c
index 03252af..62a4904 100644 (file)
--- 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 8fd9009..6e067dc 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1189,6 +1189,7 @@ struct blk_plug {
        struct list_head cb_list; /* md requires an unplug callback */
        unsigned short rq_count;
        bool multiple_queues;
+       bool nowait;
 };
 #define BLK_MAX_REQUEST_COUNT 16
 #define BLK_PLUG_FLUSH_SIZE (128 * 1024)