[PATCH] fuse: fix conversion of fuse_reverse_inval_entry() to start_removing()

[Christian Brauner]

On Fri, Dec 05, 2025 at 02:09:41PM +0100, Christian Brauner wrote:
> On Mon, Dec 01, 2025 at 03:03:08PM +0100, Miklos Szeredi wrote:
> > On Mon, 1 Dec 2025 at 09:33, Al Viro <viro at zeniv.linux.org.uk> wrote:
> > >
> > > On Mon, Dec 01, 2025 at 09:22:54AM +0100, Amir Goldstein wrote:
> > >
> > > > I don't think there is a point in optimizing parallel dir operations
> > > > with FUSE server cache invalidation, but maybe I am missing
> > > > something.
> > >
> > > The interesting part is the expected semantics of operation;
> > > d_invalidate() side definitely doesn't need any of that cruft,
> > > but I would really like to understand what that function
> > > is supposed to do.
> > >
> > > Miklos, could you post a brain dump on that?
> > 
> > This function is supposed to invalidate a dentry due to remote changes
> > (FUSE_NOTIFY_INVAL_ENTRY).  Originally it was supplied a parent ID and
> > a name and called d_invalidate() on the looked up dentry.
> > 
> > Then it grew a variant (FUSE_NOTIFY_DELETE) that was also supplied a
> > child ID, which was matched against the looked up inode.  This was
> > commit 451d0f599934 ("FUSE: Notifying the kernel of deletion."),
> > Apparently this worked around the fact that at that time
> > d_invalidate() returned -EBUSY if the target was still in use and
> > didn't unhash the dentry in that case.
> > 
> > That was later changed by commit bafc9b754f75 ("vfs: More precise
> > tests in d_invalidate") to unconditionally unhash the target, which
> > effectively made FUSE_NOTIFY_INVAL_ENTRY and FUSE_NOTIFY_DELETE
> > equivalent and the code in question unnecessary.
> > 
> > For the future, we could also introduce FUSE_NOTIFY_MOVE, that would
> > differentiate between a delete and a move, while
> > FUSE_NOTIFY_INVAL_ENTRY would continue to be the common (deleted or
> > moved) notification.
> > 
> > Attaching untested patch to remove this cruft.
> 
> Should we revert the fuse specific bits of c9ba789dad15 ("VFS: introduce
> start_creating_noperm() and start_removing_noperm()") and then apply
> your changes afterwards?

I think we shouldn't have this sitting around indefinitely so it would
be good if we'd get a nod that this is ok or someone sending revert +
fix that I can pick up. :)