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

[Miklos Szeredi]

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.

Thanks,
Miklos