block: Move checking GENHD_FL_NO_PART to bdev_add_partition()

Commit 1a721de8 ("block: don't add or resize partition on the disk
with GENHD_FL_NO_PART") prevented all operations about partitions on disks
with GENHD_FL_NO_PART in blkpg_do_ioctl() since they are meaningless.
However, it changed error code in some scenarios. So move checking
GENHD_FL_NO_PART to bdev_add_partition() to eliminate impact.

Fixes: 1a721de8 ("block: don't add or resize partition on the disk with GENHD_FL_NO_PART")
Reported-by: Allison Karlitskaya <allison.karlitskaya@redhat.com>
Closes: https://lore.kernel.org/all/CAOYeF9VsmqKMcQjo1k6YkGNujwN-nzfxY17N3F-CMikE1tYp+w@mail.gmail.com/Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20240118130401.792757-1-lilingfeng@huaweicloud.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/ioctl.c

@@ -20,8 +20,6 @@ static int blkpg_do_ioctl(struct block_device *bdev,
 	struct blkpg_partition p;
 	sector_t start, length;
 
-	if (disk->flags & GENHD_FL_NO_PART)
-		return -EINVAL;
 	if (!capable(CAP_SYS_ADMIN))
 		return -EACCES;
 	if (copy_from_user(&p, upart, sizeof(struct blkpg_partition)))

block/partitions/core.c

@@ -439,6 +439,11 @@ int bdev_add_partition(struct gendisk *disk, int partno, sector_t start,
 		goto out;
 	}
 
+	if (disk->flags & GENHD_FL_NO_PART) {
+		ret = -EINVAL;
+		goto out;
+	}
+
 	if (partition_overlaps(disk, start, length, -1)) {
 		ret = -EBUSY;
 		goto out;