block: Introduce helper to reset queue limits to default values

DM reuses the request queue when swapping in a new device table
Introduce blk_set_default_limits() which can be used to reset the the
queue_limits prior to stacking devices.

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

2 files changed, 28 insertions, 6 deletions

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 138610b98956..7541ea4bf9fe 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -96,6 +96,31 @@ void blk_queue_lld_busy(struct request_queue *q, lld_busy_fn *fn)
 EXPORT_SYMBOL_GPL(blk_queue_lld_busy);
 
 /**
+ * blk_set_default_limits - reset limits to default values
+ * @limits:  the queue_limits structure to reset
+ *
+ * Description:
+ *   Returns a queue_limit struct to its default state.  Can be used by
+ *   stacking drivers like DM that stage table swaps and reuse an
+ *   existing device queue.
+ */
+void blk_set_default_limits(struct queue_limits *lim)
+{
+        lim->max_phys_segments = MAX_PHYS_SEGMENTS;
+        lim->max_hw_segments = MAX_HW_SEGMENTS;
+        lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
+        lim->max_segment_size = MAX_SEGMENT_SIZE;
+        lim->max_sectors = lim->max_hw_sectors = SAFE_MAX_SECTORS;
+        lim->logical_block_size = lim->physical_block_size = lim->io_min = 512;
+        lim->bounce_pfn = BLK_BOUNCE_ANY;
+        lim->alignment_offset = 0;
+        lim->io_opt = 0;
+        lim->misaligned = 0;
+        lim->no_cluster = 0;
+}
+EXPORT_SYMBOL(blk_set_default_limits);
+
+/**
  * blk_queue_make_request - define an alternate make_request function for a device
  * @q:  the request queue for the device to be affected
  * @mfn: the alternate make_request function
@@ -123,14 +148,8 @@ void blk_queue_make_request(struct request_queue *q, make_request_fn *mfn)
          * set defaults
          */
         q->nr_requests = BLKDEV_MAX_RQ;
-        blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
-        blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
-        blk_queue_segment_boundary(q, BLK_SEG_BOUNDARY_MASK);
-        blk_queue_max_segment_size(q, MAX_SEGMENT_SIZE);
 
         q->make_request_fn = mfn;
-        blk_queue_max_sectors(q, SAFE_MAX_SECTORS);
-        blk_queue_logical_block_size(q, 512);
         blk_queue_dma_alignment(q, 511);
         blk_queue_congestion_threshold(q);
         q->nr_batching = BLK_BATCH_REQ;
@@ -143,6 +162,8 @@ void blk_queue_make_request(struct request_queue *q, make_request_fn *mfn)
         q->unplug_timer.function = blk_unplug_timeout;
         q->unplug_timer.data = (unsigned long)q;
 
+        blk_set_default_limits(&q->limits);
+
         /*
          * by default assume old behaviour and bounce for any highmem page
          */
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 0b1a6cae9de1..8963d9149b5f 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -926,6 +926,7 @@ extern void blk_queue_alignment_offset(struct request_queue *q,
                                        unsigned int alignment);
 extern void blk_queue_io_min(struct request_queue *q, unsigned int min);
 extern void blk_queue_io_opt(struct request_queue *q, unsigned int opt);
+extern void blk_set_default_limits(struct queue_limits *lim);
 extern int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
                             sector_t offset);
 extern void disk_stack_limits(struct gendisk *disk, struct block_device *bdev,