blk-mq: add tag allocation policy

This is the blk-mq part to support tag allocation policy. The default
allocation policy isn't changed (though it's not a strict FIFO). The new
policy is round-robin for libata. But it's a try-best implementation. If
multiple tasks are competing, the tags returned will be mixed (which is
unavoidable even with !mq, as requests from different tasks can be
mixed in queue)

Cc: Jens Axboe <axboe@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 5b6500c77ed2..86b08b1a5eba 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -147,6 +147,8 @@ enum {
         BLK_MQ_F_SG_MERGE       = 1 << 2,
         BLK_MQ_F_SYSFS_UP       = 1 << 3,
         BLK_MQ_F_DEFER_ISSUE    = 1 << 4,
+        BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,
+        BLK_MQ_F_ALLOC_POLICY_BITS = 1,
 
         BLK_MQ_S_STOPPED        = 0,
         BLK_MQ_S_TAG_ACTIVE     = 1,
@@ -155,6 +157,12 @@ enum {
 
         BLK_MQ_CPU_WORK_BATCH   = 8,
 };
+#define BLK_MQ_FLAG_TO_ALLOC_POLICY(flags) \
+        ((flags >> BLK_MQ_F_ALLOC_POLICY_START_BIT) & \
+                ((1 << BLK_MQ_F_ALLOC_POLICY_BITS) - 1))
+#define BLK_ALLOC_POLICY_TO_MQ_FLAG(policy) \
+        ((policy & ((1 << BLK_MQ_F_ALLOC_POLICY_BITS) - 1)) \
+                << BLK_MQ_F_ALLOC_POLICY_START_BIT)
 
 struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *);
 void blk_mq_finish_init(struct request_queue *q);