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

[Christoph Hellwig <hch@infradead.org>]

On Mon, Jul 07, 2025 at 05:45:32PM -0700, Darrick J. Wong wrote:
> On second thought -- it's weird that you'd flush the filesystem and
> shrink the inode/dentry caches in a "your device went away" handler.
> Fancy filesystems like bcachefs and btrfs would likely just shift IO to
> a different bdev, right?  And there's no good reason to run shrinkers on
> either of those fses, right?

No nmeed for fancy file systems, this is weird no matter what.  But it
is what Linux has done for 30+ years, so I kept it when refactoring
this code to sit in a callback.

> > 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.  I don't understand
> why you need a "generic" solution for btrfs when it's not going to do
> what the others do anyway.

Why?  You're most likely to get the locking wrong, and so on.

What might make sense is to move the sync_filesystem, shrink_dcache_sb
and evict_inodes into the method.  That way file systems where we

> As an aside:
> 'twould be nice if we could lift the *FS_IOC_SHUTDOWN dispatch out of
> everyone's ioctl functions into the VFS, and then move the "I am dead"
> state into super_block so that you could actually shut down any
> filesystem, not just the seven that currently implement it.

Sure.  Someone just needs to do the work..