block: allow deleting zero length partition

delete_partition() was noop for zero length partition.  As the
addition code allows creating zero lenght partition and deletion is
assumed to always succeed, this causes memory leak for zero length
partitions.  Allow zero length partitions to end their meaningless
lives.

While at it, allow deleting zero lenght partition via
BLKPG_DEL_PARTITION ioctl too.
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/ioctl.c

@@ -68,8 +68,6 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg __user
 		case BLKPG_DEL_PARTITION:
 			if (!disk->part[part-1])
 				return -ENXIO;
-			if (disk->part[part - 1]->nr_sects == 0)
-				return -ENXIO;
 			bdevp = bdget_disk(disk, part);
 			if (!bdevp)
 				return -ENOMEM;

fs/partitions/check.c

@@ -325,8 +325,6 @@ void delete_partition(struct gendisk *disk, int part)
 
 	if (!p)
 		return;
-	if (!p->nr_sects)
-		return;
 	disk->part[part-1] = NULL;
 	p->start_sect = 0;
 	p->nr_sects = 0;