[dm-devel] [PATCH 3/3] block: allow 'chunk_sectors' to be non-power-of-2

[Mike Snitzer]

It is possible for a block device to use a non power-of-2 for chunk
size which results in a full-stripe size that is also a non
power-of-2.

Update blk_queue_chunk_sectors() and blk_max_size_offset() to
accommodate drivers that need a non power-of-2 chunk_sectors.

Signed-off-by: Mike Snitzer <snitzer at redhat.com>
---
 block/blk-settings.c   | 10 ++++------
 include/linux/blkdev.h | 12 +++++++++---
 2 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index b09642d5f15e..e40a162cc946 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -172,15 +172,13 @@ EXPORT_SYMBOL(blk_queue_max_hw_sectors);
  *
  * Description:
  *    If a driver doesn't want IOs to cross a given chunk size, it can set
- *    this limit and prevent merging across chunks. Note that the chunk size
- *    must currently be a power-of-2 in sectors. Also note that the block
- *    layer must accept a page worth of data at any offset. So if the
- *    crossing of chunks is a hard limitation in the driver, it must still be
- *    prepared to split single page bios.
+ *    this limit and prevent merging across chunks. Note that the block layer
+ *    must accept a page worth of data at any offset. So if the crossing of
+ *    chunks is a hard limitation in the driver, it must still be prepared
+ *    to split single page bios.
  **/
 void blk_queue_chunk_sectors(struct request_queue *q, unsigned int chunk_sectors)
 {
-	BUG_ON(!is_power_of_2(chunk_sectors));
 	q->limits.chunk_sectors = chunk_sectors;
 }
 EXPORT_SYMBOL(blk_queue_chunk_sectors);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 453a3d735d66..e72bcce22143 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1059,11 +1059,17 @@ static inline unsigned int blk_queue_get_max_sectors(struct request_queue *q,
 static inline unsigned int blk_max_size_offset(struct request_queue *q,
 					       sector_t offset)
 {
-	if (!q->limits.chunk_sectors)
+	unsigned int chunk_sectors = q->limits.chunk_sectors;
+
+	if (!chunk_sectors)
 		return q->limits.max_sectors;
 
-	return min(q->limits.max_sectors, (unsigned int)(q->limits.chunk_sectors -
-			(offset & (q->limits.chunk_sectors - 1))));
+	if (is_power_of_2(chunk_sectors))
+		chunk_sectors -= (offset & (chunk_sectors - 1));
+	else
+		chunk_sectors -= sector_div(offset, chunk_sectors);
+
+	return min(q->limits.max_sectors, chunk_sectors);
 }
 
 static inline unsigned int blk_rq_get_max_sectors(struct request *rq,
-- 
2.15.0