linux-kernel - Re: [RFC PATCH v2 4/6] fuse: implementation of the FUSE_LOOKUP

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Message-ID: <CAJfpegvxLqpa0ttnEjY1W1Oqf5vpw3uKrrf8y5DdnuXcnQJzNg@mail.gmail.com>
Date: Fri, 9 Jan 2026 17:28:30 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: Bernd Schubert <bschubert@....com>
Cc: Amir Goldstein <amir73il@...il.com>, Luis Henriques <luis@...lia.com>, 
	"Darrick J. Wong" <djwong@...nel.org>, Kevin Chen <kchen@....com>, 
	Horst Birthelmer <hbirthelmer@....com>, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Matt Harvey <mharvey@...ptrading.com>, 
	kernel-dev@...lia.com
Subject: Re: [RFC PATCH v2 4/6] fuse: implementation of the FUSE_LOOKUP_HANDLE operation

On Fri, 9 Jan 2026 at 16:56, Bernd Schubert <bschubert@....com> wrote:

> Feasible, but we should extend io-uring to FUSE_NOTIFY first, otherwise
> this will have a painful overhead.

We don't want to do the lock/add/unlock for individual dentries
anyway, so might as well make this FUSE_NOTIFY_ENTRIES.  That would
lock the directory, add a bunch of dentries, then unlock.

The fun part is that locking the directory must not be done from the
READDIR context, as rwsem read locks are apparently not nestable.
This would make the interface a pain to use.  We could work around
that by checking if a READDIR is currently in progress and then
synchronizing the two such that the entries are added with the
directory lock held.   It's a bit of complexity, but maybe worth it as
it's going to be the common usage.

Thanks,
Miklos