dm: merge max_hw_sector

Make sure dm honours max_hw_sectors of underlying devices

  We still have no firm testing evidence in support of this patch but
  believe it may help to resolve some bug reports.  - agk

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-table.c

@@ -99,6 +99,9 @@ static void combine_restrictions_low(struct io_restrictions *lhs,
 	lhs->max_segment_size =
 		min_not_zero(lhs->max_segment_size, rhs->max_segment_size);
 
+	lhs->max_hw_sectors =
+		min_not_zero(lhs->max_hw_sectors, rhs->max_hw_sectors);
+
 	lhs->seg_boundary_mask =
 		min_not_zero(lhs->seg_boundary_mask, rhs->seg_boundary_mask);
 
@@ -566,6 +569,9 @@ void dm_set_device_limits(struct dm_target *ti, struct block_device *bdev)
 	rs->max_segment_size =
 		min_not_zero(rs->max_segment_size, q->max_segment_size);
 
+	rs->max_hw_sectors =
+		min_not_zero(rs->max_hw_sectors, q->max_hw_sectors);
+
 	rs->seg_boundary_mask =
 		min_not_zero(rs->seg_boundary_mask,
 			     q->seg_boundary_mask);
@@ -703,6 +709,8 @@ static void check_for_valid_limits(struct io_restrictions *rs)
 {
 	if (!rs->max_sectors)
 		rs->max_sectors = SAFE_MAX_SECTORS;
+	if (!rs->max_hw_sectors)
+		rs->max_hw_sectors = SAFE_MAX_SECTORS;
 	if (!rs->max_phys_segments)
 		rs->max_phys_segments = MAX_PHYS_SEGMENTS;
 	if (!rs->max_hw_segments)
@@ -901,6 +909,7 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q)
 	q->max_hw_segments = t->limits.max_hw_segments;
 	q->hardsect_size = t->limits.hardsect_size;
 	q->max_segment_size = t->limits.max_segment_size;
+	q->max_hw_sectors = t->limits.max_hw_sectors;
 	q->seg_boundary_mask = t->limits.seg_boundary_mask;
 	q->bounce_pfn = t->limits.bounce_pfn;
 	if (t->limits.no_cluster)

include/linux/device-mapper.h

@@ -115,6 +115,7 @@ struct io_restrictions {
 	unsigned short		max_hw_segments;
 	unsigned short		hardsect_size;
 	unsigned int		max_segment_size;
+	unsigned int		max_hw_sectors;
 	unsigned long		seg_boundary_mask;
 	unsigned long		bounce_pfn;
 	unsigned char		no_cluster; /* inverted so that 0 is default */