linux-kernel - Re: [PATCH] fuse: fix conversion of fuse_reverse_inval_entry() to start

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Message-ID: <CAJfpegs+o01jgY76WsGnk9j41LS5V0JQSk--d6xsJJp4VjTh8Q@mail.gmail.com>
Date: Mon, 1 Dec 2025 15:03:08 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Amir Goldstein <amir73il@...il.com>, NeilBrown <neil@...wn.name>, 
	Christian Brauner <brauner@...nel.org>, Val Packett <val@...kett.cool>, Jan Kara <jack@...e.cz>, 
	linux-fsdevel@...r.kernel.org, Jeff Layton <jlayton@...nel.org>, 
	Chris Mason <clm@...com>, David Sterba <dsterba@...e.com>, David Howells <dhowells@...hat.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Danilo Krummrich <dakr@...nel.org>, Tyler Hicks <code@...icks.com>, Chuck Lever <chuck.lever@...cle.com>, 
	Olga Kornievskaia <okorniev@...hat.com>, Dai Ngo <Dai.Ngo@...cle.com>, 
	Namjae Jeon <linkinjeon@...nel.org>, Steve French <smfrench@...il.com>, 
	Sergey Senozhatsky <senozhatsky@...omium.org>, Carlos Maiolino <cem@...nel.org>, 
	John Johansen <john.johansen@...onical.com>, Paul Moore <paul@...l-moore.com>, 
	James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, 
	Stephen Smalley <stephen.smalley.work@...il.com>, Ondrej Mosnacek <omosnace@...hat.com>, 
	Mateusz Guzik <mjguzik@...il.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	Stefan Berger <stefanb@...ux.ibm.com>, "Darrick J. Wong" <djwong@...nel.org>, linux-kernel@...r.kernel.org, 
	netfs@...ts.linux.dev, ecryptfs@...r.kernel.org, linux-nfs@...r.kernel.org, 
	linux-unionfs@...r.kernel.org, linux-cifs@...r.kernel.org, 
	linux-xfs@...r.kernel.org, linux-security-module@...r.kernel.org, 
	selinux@...r.kernel.org
Subject: Re: [PATCH] fuse: fix conversion of fuse_reverse_inval_entry() to start_removing()

On Mon, 1 Dec 2025 at 09:33, Al Viro <viro@...iv.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

View attachment "fuse-notify_inval_entry-and-notify_delete-are-equivalent.patch" of type "text/x-patch" (1022 bytes)