Re: [PATCH 0/3] fanotify support for btrfs sub-volumes

Christoph Hellwig
2023-11-08T14:08:14Z

On Wed, Nov 08, 2023 at 09:27:44AM +0100, Christian Brauner wrote:
> > What is that flag going to buy us?
>
> The initial list that Josef provided in
> https://lore.kernel.org/linux-btrfs/20231025210654.GA2892534@perftesting
> asks to give users a way to figure out whether a file is located on a
> subvolume. Which I think is reasonable and there's a good chunk of
> software out there that could really benefit from this. Now all of the
> additional info that is requested doesn't need to live in statx(). But
> that flag can serve as an indicator for userspace that they are on a
> subvolume and that they can go to btrfs specific ioctls if they want to
> figure out more details.

Well, if we want to legitimize the historic btrfs behavior the way to
find out is if st_dev changes without that being a mount point, so
an extra flag would be redundant.