[PATCH] [BLOCK] Allow tag 0 to be generated

[Luben Tuikov <ltuikov@yahoo.com>]

Commit 67869fb9fdfa04503b250d59e086c15f1698aea0
skipped tag 0 by virtue of setting last_tag to
0. This commit sets it to -1, in order to start
and loop over from 0, thus generating tags
[0,max_tag-1], instead of [1,max_tag-1].

Signed-off-by: Luben Tuikov <ltuikov@yahoo.com>
---
 For a reference to the original patch see here:
 git://github.com/ltuikov/linux-2.6.git

 block/blk-tag.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/block/blk-tag.c b/block/blk-tag.c
index f792e98..744cea6 100644
--- a/block/blk-tag.c
+++ b/block/blk-tag.c
@@ -130,7 +130,7 @@ init_tag_map(struct request_queue *q, struct blk_queue_tag *tags, int depth)
        tags->max_depth = depth;
        tags->tag_index = tag_index;
        tags->tag_map = tag_map;
-       tags->last_tag = 0;
+       tags->last_tag = -1;
 
        return 0;
 fail:
@@ -340,7 +340,7 @@ EXPORT_SYMBOL(blk_queue_end_tag);
 int blk_queue_start_tag(struct request_queue *q, struct request *rq)
 {
        struct blk_queue_tag *bqt = q->queue_tags;
-       unsigned max_depth;
+       int max_depth;
        int tag;
 
        if (unlikely((rq->cmd_flags & REQ_QUEUED))) {
@@ -361,14 +361,14 @@ int blk_queue_start_tag(struct request_queue *q, struct request *rq)
        max_depth = bqt->max_depth;
        if (!rq_is_sync(rq) && max_depth > 1) {
                max_depth -= 2;
-               if (!max_depth)
+               if (max_depth <= 0)
                        max_depth = 1;
                if (q->in_flight[BLK_RW_ASYNC] > max_depth)
                        return 1;
        }
 
        if (bqt->last_tag == bqt->max_depth-1)
-               bqt->last_tag = 0;
+               bqt->last_tag = -1;
 
        do {
                tag = find_next_zero_bit(bqt->tag_map,
-- 
1.7.2.2.165.gbc382