Re: [dm-devel] [PATCH 01/26] block: refactor device number setup in __device_add_disk

Christoph Hellwig
2021-05-24T07:20:20Z

On Fri, May 21, 2021 at 05:16:46PM +0000, Luis Chamberlain wrote:
> > - /* 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 ...
>
> > 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.