DM: Fix device mapper topology stacking

Make DM use bdev_stack_limits() function so that partition offsets get
taken into account when calculating alignment. Clarify stacking
warnings.

Also remove obsolete clearing of final alignment_offset and misalignment
flag.

Signed-off-by: Martin K. Petersen <[e-mail]>
Signed-off-by: Mike Snitzer <[e-mail]>
Cc: Alasdair G. Kergon <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/md/dm-table.c

···
 		return 0;
 	}
 
-	if (blk_stack_limits(limits, &q->limits, start << 9) < 0)
-		DMWARN("%s: target device %s is misaligned: "
+	if (bdev_stack_limits(limits, bdev, start) < 0)
+		DMWARN("%s: adding target device %s caused an alignment inconsistency: "
 		       "physical_block_size=%u, logical_block_size=%u, "
 		       "alignment_offset=%u, start=%llu",
 		       dm_device_name(ti->table->md), bdevname(bdev, b),
 		       q->limits.physical_block_size,
 		       q->limits.logical_block_size,
 		       q->limits.alignment_offset,
-		       (unsigned long long) start << 9);
-
+		       (unsigned long long) start << SECTOR_SHIFT);
 
 	/*
 	 * Check if merge fn is supported.
···
 		 * for the table.
 		 */
 		if (blk_stack_limits(limits, &ti_limits, 0) < 0)
-			DMWARN("%s: target device "
+			DMWARN("%s: adding target device "
 			       "(start sect %llu len %llu) "
-			       "is misaligned",
+			       "caused an alignment inconsistency",
 			       dm_device_name(table->md),
 			       (unsigned long long) ti->begin,
 			       (unsigned long long) ti->len);
···
 void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 			       struct queue_limits *limits)
 {
-	/*
-	 * Each target device in the table has a data area that should normally
-	 * be aligned such that the DM device's alignment_offset is 0.
-	 * FIXME: Propagate alignment_offsets up the stack and warn of
-	 *	  sub-optimal or inconsistent settings.
-	 */
-	limits->alignment_offset = 0;
-	limits->misaligned = 0;
-
 	/*
 	 * Copy table's limits to the DM device's request_queue
 	 */