block: bdev_stack_limits wrapper

DM does not want to know about partition offsets.  Add a partition-aware
wrapper that DM can use when stacking block devices.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Reviewed-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 127f82551855..5eeb9e0d256e 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -640,6 +640,28 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 EXPORT_SYMBOL(blk_stack_limits);
 
 /**
+ * bdev_stack_limits - adjust queue limits for stacked drivers
+ * @t:  the stacking driver limits (top device)
+ * @bdev:  the component block_device (bottom)
+ * @start:  first data sector within component device
+ *
+ * Description:
+ *    Merges queue limits for a top device and a block_device.  Returns
+ *    0 if alignment didn't change.  Returns -1 if adding the bottom
+ *    device caused misalignment.
+ */
+int bdev_stack_limits(struct queue_limits *t, struct block_device *bdev,
+                      sector_t start)
+{
+        struct request_queue *bq = bdev_get_queue(bdev);
+
+        start += get_start_sect(bdev);
+
+        return blk_stack_limits(t, &bq->limits, start << 9);
+}
+EXPORT_SYMBOL(bdev_stack_limits);
+
+/**
  * disk_stack_limits - adjust queue limits for stacked drivers
  * @disk:  MD/DM gendisk (top)
  * @bdev:  the underlying block device (bottom)