block: Deprecate QUEUE_FLAG_CLUSTER and use queue_limits instead

When stacking devices, a request_queue is not always available. This
forced us to have a no_cluster flag in the queue_limits that could be
used as a carrier until the request_queue had been set up for a
metadevice.

There were several problems with that approach. First of all it was up
to the stacking device to remember to set queue flag after stacking had
completed. Also, the queue flag and the queue limits had to be kept in
sync at all times. We got that wrong, which could lead to us issuing
commands that went beyond the max scatterlist limit set by the driver.

The proper fix is to avoid having two flags for tracking the same thing.
We deprecate QUEUE_FLAG_CLUSTER and use the queue limit directly in the
block layer merging functions. The queue_limit 'no_cluster' is turned
into 'cluster' to avoid double negatives and to ease stacking.
Clustering defaults to being enabled as before. The queue flag logic is
removed from the stacking function, and explicitly setting the cluster
flag is no longer necessary in DM and MD.

Reported-by: Ed Lin <ed.lin@promise.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index aae86fd10c4f..95aeeeb49e8b 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -250,7 +250,7 @@ struct queue_limits {
 
 	unsigned char		misaligned;
 	unsigned char		discard_misaligned;
-	unsigned char		no_cluster;
+	unsigned char		cluster;
 	signed char		discard_zeroes_data;
 };
 
@@ -380,7 +380,6 @@ struct request_queue
 #endif
 };
 
-#define QUEUE_FLAG_CLUSTER	0	/* cluster several segments into 1 */
 #define QUEUE_FLAG_QUEUED	1	/* uses generic tag queueing */
 #define QUEUE_FLAG_STOPPED	2	/* queue is stopped */
 #define	QUEUE_FLAG_SYNCFULL	3	/* read queue has been filled */
@@ -403,7 +402,6 @@ struct request_queue
 #define QUEUE_FLAG_SECDISCARD  19	/* supports SECDISCARD */
 
 #define QUEUE_FLAG_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\
-				 (1 << QUEUE_FLAG_CLUSTER) |		\
 				 (1 << QUEUE_FLAG_STACKABLE)	|	\
 				 (1 << QUEUE_FLAG_SAME_COMP)	|	\
 				 (1 << QUEUE_FLAG_ADD_RANDOM))
@@ -510,6 +508,11 @@ static inline void queue_flag_clear(unsigned int flag, struct request_queue *q)
 
 #define rq_data_dir(rq)		((rq)->cmd_flags & 1)
 
+static inline unsigned int blk_queue_cluster(struct request_queue *q)
+{
+	return q->limits.cluster;
+}
+
 /*
  * We regard a request as sync, if either a read or a sync write
  */