blk-mq: allow REQ_NOWAIT to return an error inline

By default, if a caller sets REQ_NOWAIT and we need to block, we'll
return -EAGAIN through the bio->bi_end_io() callback. For some use
cases, this makes it hard to use.

Allow a caller to ask for inline return of errors related to
blocking by also setting REQ_NOWAIT_INLINE.

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

diff --git a/block/blk-mq.c b/block/blk-mq.c
index b038ec6..2bc2c07 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1960,9 +1960,13 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
        rq = blk_mq_get_request(q, bio, &data);
        if (unlikely(!rq)) {
                rq_qos_cleanup(q, bio);
-               if (bio->bi_opf & REQ_NOWAIT)
+
+               cookie = BLK_QC_T_NONE;
+               if (bio->bi_opf & REQ_NOWAIT_INLINE)
+                       cookie = BLK_QC_T_EAGAIN;
+               else if (bio->bi_opf & REQ_NOWAIT)
                        bio_wouldblock_error(bio);
-               return BLK_QC_T_NONE;
+               return cookie;
        }
 
        trace_block_getrq(q, bio, bio->bi_opf);

diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index feff3fe..1b1fa15 100644 (file)
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -311,6 +311,7 @@ enum req_flag_bits {
        __REQ_RAHEAD,           /* read ahead, can fail anytime */
        __REQ_BACKGROUND,       /* background IO */
        __REQ_NOWAIT,           /* Don't wait if request will block */
+       __REQ_NOWAIT_INLINE,    /* Return would-block error inline */
        /*
         * When a shared kthread needs to issue a bio for a cgroup, doing
         * so synchronously can lead to priority inversions as the kthread
@@ -345,6 +346,7 @@ enum req_flag_bits {
 #define REQ_RAHEAD             (1ULL << __REQ_RAHEAD)
 #define REQ_BACKGROUND         (1ULL << __REQ_BACKGROUND)
 #define REQ_NOWAIT             (1ULL << __REQ_NOWAIT)
+#define REQ_NOWAIT_INLINE      (1ULL << __REQ_NOWAIT_INLINE)
 #define REQ_CGROUP_PUNT                (1ULL << __REQ_CGROUP_PUNT)
 
 #define REQ_NOUNMAP            (1ULL << __REQ_NOUNMAP)
@@ -418,12 +420,13 @@ static inline int op_stat_group(unsigned int op)
 
 typedef unsigned int blk_qc_t;
 #define BLK_QC_T_NONE          -1U
+#define BLK_QC_T_EAGAIN                -2U
 #define BLK_QC_T_SHIFT         16
 #define BLK_QC_T_INTERNAL      (1U << 31)
 
 static inline bool blk_qc_t_valid(blk_qc_t cookie)
 {
-       return cookie != BLK_QC_T_NONE;
+       return cookie != BLK_QC_T_NONE && cookie != BLK_QC_T_EAGAIN;
 }
 
 static inline unsigned int blk_qc_t_to_queue_num(blk_qc_t cookie)