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

[Christoph Hellwig]

On Tue, Jun 02, 2026 at 12:10:08PM +0200, Christian Brauner wrote:
> fs_holder_ops recovers the owning superblock from bdev->bd_holder, which
> forces the holder to be exactly one superblock and prevents several
> superblocks from sharing one block device. That's what erofs is doing.
> 
> Introduce a global dev_t-keyed rhltable mapping each block device to the
> superblock(s) using it. The holder argument becomes purely the block
> layer's exclusivity token (a superblock, or a file_system_type for
> shared devices) and is no longer needed by the fs specific callbacks.

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.

IMHO sharing devices between superblocks is a bad idea, but that ship
has sailed, but please keep it contained inside of erofs.