block: remove the discard_alignment field from struct hd_struct

The alignment offset is only used in slow path callers, so just calculate
it on the fly.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/partitions/core.c

@@ -209,7 +209,10 @@ static ssize_t part_discard_alignment_show(struct device *dev,
 					   struct device_attribute *attr, char *buf)
 {
 	struct hd_struct *p = dev_to_part(dev);
-	return sprintf(buf, "%u\n", p->discard_alignment);
+
+	return sprintf(buf, "%u\n",
+		queue_limit_discard_alignment(&part_to_disk(p)->queue->limits,
+				p->start_sect));
 }
 
 static DEVICE_ATTR(partition, 0444, part_partition_show, NULL);
@@ -408,8 +411,6 @@ static struct hd_struct *add_partition(struct gendisk *disk, int partno,
 	pdev = part_to_dev(p);
 
 	p->start_sect = start;
-	p->discard_alignment =
-		queue_limit_discard_alignment(&disk->queue->limits, start);
 	p->nr_sects = len;
 	p->partno = partno;
 	p->policy = get_disk_ro(disk);

include/linux/blkdev.h

@@ -1498,8 +1498,8 @@ static inline int bdev_discard_alignment(struct block_device *bdev)
 	struct request_queue *q = bdev_get_queue(bdev);
 
 	if (bdev != bdev->bd_contains)
-		return bdev->bd_part->discard_alignment;
-
+		return queue_limit_discard_alignment(&q->limits,
+				bdev->bd_part->start_sect);
 	return q->limits.discard_alignment;
 }
 

include/linux/genhd.h

@@ -65,7 +65,6 @@ struct hd_struct {
 	struct disk_stats __percpu *dkstats;
 	struct percpu_ref ref;
 
-	unsigned int discard_alignment;
 	struct device __dev;
 	struct kobject *holder_dir;
 	int policy, partno;