Re: bd_holder

[Christoph Hellwig <hch@lst.de>]

On Mon, Aug 07, 2023 at 11:28:54AM +0200, Christian Brauner wrote:
> I've been looking into reducing sb_lock and replacing it mostly with a
> new file_system_type->fs_super_lock which would be a
> per-file-system-type spinlock protecting fs_type->fs_supers.
> 
> With the changes in vfs.super bd_holder always stores the super_block
> and so we should be able to get rid of get_super() and user_get_super()
> completely. Am I right in this or is there something that would prevent
> us from doing something like the following (completely untested sketch)?:

I have a series killing get_super, and it looks pretty similar to what
you've proposed.  I'm completely under water right now but I hope can
get it into a good enough shape to post it later today or tomorrow.

user_get_super OTOH can't go away.  It's only used in two legacy APIs
where it must only work for the device in s_dev.  It's not performance
critical and we could use other lookup schemes.

get_active_super can go away, but with Darrick having queued up work
in this area it'll have to wait for next merge window.