Re: [PATCH RFC 2/8] fs: add a global device to super block hash table

[Christoph Hellwig <hch@lst.de>]

On Tue, Jun 16, 2026 at 04:59:53PM +0200, Christian Brauner wrote:
> > Err, no.  block devices need to have a specific owner.  If erofs wants
> > to share a device between superblock it needs to come up with an entity
> > that owns the block devices which is not a superblock.
> 
> It already did.
> 
> > IMHO sharing devices between superblocks is a bad idea, but that ship
> > has sailed, but please keep it contained inside of erofs.
> 
> We need a simple device number to superblock mapping anyway and that can
> simply be centralized in the vfs. And it can work with anon device
> numbers and block device numbers uniformly.

No, we don't need a secondary device number to sb mapping.  On the other
hand we do need the deviceloss, freeze etc upcalls to work for owners
that are not file systems like mdraid or dm, even if they have been
slow to pick this.  The whole idea of the holder ops is to abstract
away from who holds it instead of adding back the broken hard coding
of the superblock.  Otherwise you're just badly reinventing get_super.

If erofs already has an owner entity it just needs custom holder ops for
that.