On Fri, May 21, 2021 at 05:16:46PM +0000, Luis Chamberlain wrote:

quoted

-	/* in consecutive minor range? */
-	if (bdev->bd_partno < disk->minors) {
-		*devt = MKDEV(disk->major, disk->first_minor + bdev->bd_partno);
-		return 0;
-	}
-

It is not obviously clear to me, why this was part of add_disk()
path, and ...

quoted

diff --git a/block/partitions/core.c b/block/partitions/core.c
index dc60ecf46fe6..504297bdc8bf 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c

@@ -379,9 +380,15 @@ static struct block_device *add_partition(struct gendisk *disk, int partno,
 	pdev->type = &part_type;
 	pdev->parent = ddev;
 
-	err = blk_alloc_devt(bdev, &devt);
-	if (err)
-		goto out_put;
+	/* in consecutive minor range? */
+	if (bdev->bd_partno < disk->minors) {
+		devt = MKDEV(disk->major, disk->first_minor + bdev->bd_partno);
+	} else {
+		err = blk_alloc_ext_minor();
+		if (err < 0)
+			goto out_put;
+		devt = MKDEV(BLOCK_EXT_MAJOR, err);
+	}
 	pdev->devt = devt;
 
 	/* delay uevent until 'holders' subdir is created */

... and why we only add this here now.

For the genhd minors == 0 (aka GENHD_FL_EXT_DEVT) implies having to
allocate a dynamic dev_t, so it can be folded into another conditional.