file metadata via fs API (was: [GIT PULL] Filesystem Information)

[Al Viro]

On Tue, Aug 11, 2020 at 09:09:36AM -0700, Linus Torvalds wrote:
> On Tue, Aug 11, 2020 at 9:05 AM Al Viro <viro at zeniv.linux.org.uk> wrote:
> >
> > Except that you suddenly see non-directory dentries get children.
> > And a lot of dcache-related logics needs to be changed if that
> > becomes possible.
> 
> Yeah, I think you'd basically need to associate a (dynamic)
> mount-point to that path when you start doing O_ALT. Or something.

Whee...  That's going to be non-workable for xattrs - fgetxattr()
needs to work after unlink().  And you'd obviously need to prevent
crossing into that sucker on normal lookups, which would add quite
a few interesting twists around the automount points.

I'm not saying it's not doable, but it won't be anywhere near
straightforward.  And API semantics questions are still there...