block: support different tag allocation policy

The libata tag allocation is using a round-robin policy. Next patch will
make libata use block generic tag allocation, so let's add a policy to
tag allocation.

Currently two policies: FIFO (default) and round-robin.

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>

2 files changed, 5 insertions, 1 deletions

diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 019e66858ce6..e113c757d555 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -402,6 +402,9 @@ struct scsi_host_template {
          */
         unsigned char present;
 
+        /* If use block layer to manage tags, this is tag allocation policy */
+        int tag_alloc_policy;
+
         /*
          * Let the block layer assigns tags to all commands.
          */
diff --git a/include/scsi/scsi_tcq.h b/include/scsi/scsi_tcq.h
index 9708b28bd2aa..b27977e8aaed 100644
--- a/include/scsi/scsi_tcq.h
+++ b/include/scsi/scsi_tcq.h
@@ -66,7 +66,8 @@ static inline int scsi_init_shared_tag_map(struct Scsi_Host *shost, int depth)
          * devices on the shared host (for libata)
          */
         if (!shost->bqt) {
-                shost->bqt = blk_init_tags(depth);
+                shost->bqt = blk_init_tags(depth,
+                        shost->hostt->tag_alloc_policy);
                 if (!shost->bqt)
                         return -ENOMEM;
         }