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

From: Christoph Hellwig <[email-masked]>
Date: Mon, 24 May 2021 09:20:13 +0200

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.