Re: [PATCH v4 1/6] fs: enhance and rename shutdown() callback to remove_bdev()

[Dave Chinner <david@fromorbit.com>]

On Tue, Jul 08, 2025 at 12:36:48PM +0930, Qu Wenruo wrote:
> 在 2025/7/8 11:39, Qu Wenruo 写道:
> > 在 2025/7/8 10:15, Darrick J. Wong 写道:
> > > > Yes, the naming is not perfect and mixing cause and action, but the end
> > > > result is still a more generic and less duplicated code base.
> > > 
> > > I think dchinner makes a good point that if your filesystem can do
> > > something clever on device removal, it should provide its own block
> > > device holder ops instead of using fs_holder_ops.
> > 
> > Then re-implement a lot of things like bdev_super_lock()?

IDGI. Simply add:

EXPORT_SYMBOL_GPL(get_bdev_super);

And the problem is solved.

> > I'd prefer not.
> > 
> > 
> > fs_holder_ops solves a lot of things like handling mounting/inactive
> > fses, and pushing it back again to the fs code is just causing more
> > duplication.

This is all encapsulated in get_bdev_super(), so btrfs doesn't need
to implement any of this. get_bdev_super/deactivate_super is the API
you should be using with the blk_holder_ops methods.

> > Not really worthy if we only want a single different behavior.

This is the *3rd* different behaviour for ->mark_dead. We
have the generic behaviour, the bcachefs behaviour, and now the
btrfs behaviour (whatever that may be).

> > Thus I strongly prefer to do with the existing fs_holder_ops, no matter
> > if it's using/renaming the shutdown() callback, or a new callback.
> 
> Previously Christoph is against a new ->remove_bdev() callback, as it is
> conflicting with the existing ->shutdown().
> 
> So what about a new ->handle_bdev_remove() callback, that we do something
> like this inside fs_bdev_mark_dead():
> 
> {
> 	bdev_super_lock();
> 	if (!surprise)
> 		sync_filesystem();
> 
> 	if (s_op->handle_bdev_remove) {
> 		ret = s_op->handle_bdev_remove();
> 		if (!ret) {
> 			super_unlock_shared();
> 			return;
> 		}
> 	}
> 	shrink_dcache_sb();
> 	evict_inodes();
> 	if (s_op->shutdown)
> 		s_op->shutdown();
> }
> 
> So that the new ->handle_bdev_remove() is not conflicting with
> ->shutdown() but an optional one.
> 
> And if the fs can not handle the removal, just let
> ->handle_bdev_remove() return an error so that we fallback to the existing
> shutdown routine.
> 
> Would this be more acceptable?

No.

-Dave.
-- 
Dave Chinner
david@fromorbit.com