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[178.84.201.199]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6b721eedfd7sm1603106a12.31.2026.11.09.06.51.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Nov 2026 06:51:49 -0800 (PST) Date: Mon, 9 Nov 2026 15:51:49 +0100 From: Amir Goldstein To: =?iso-8859-1?B?Suly6W15?= Jean Cc: Christian Brauner , miklos@szeredi.hu, linux-unionfs@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/3] ovl: disable nfs_export for same-sb lower layers with different idmaps Message-ID: References: <20260920203239.2876221-2-Jeremy.Jean@oss.cyber.gouv.fr> <20260920203239.2876221-3-Jeremy.Jean@oss.cyber.gouv.fr> <20260925-server-hager-riskieren-06116eded213@brauner> <5e8dff576ead72fa502b7cd38889e780@oss.cyber.gouv.fr> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <5e8dff576ead72fa502b7cd38889e780@oss.cyber.gouv.fr> On Sun, Nov 08, 2026 at 08:12:49PM +0100, Jérémy Jean wrote: > On 2026-09-25 16:17, Amir Goldstein wrote: > > On Fri, Sep 25, 2026 at 3:51 PM Christian Brauner > > wrote: > > > > > > On Mon, Sep 21, 2026 at 10:10:28AM +0200, Amir Goldstein wrote: > > > > On Sun, Sep 20, 2026 at 10:33 PM Jérémy Jean > > > > wrote: > > > > > > > > > > Overlay file handles identify a backing filesystem, but not the lower > > > > > mount used to decode it. If lower layers share a superblock and use > > > > > different idmaps, a file handle can decode through the wrong layer and > > > > > initialize the overlay inode with the wrong owner. > > > > > > > > > > Track the first lower idmap seen for each ovl_sb and disable nfs_export > > > > > when another lower layer on the same backing superblock uses a different > > > > > idmap. Keep index enabled: copy up starts from the overlay dentry selected > > > > > by lookup and does not need to decode a lower file handle through another > > > > > layer. > > > > > > > > > > Fixes: bc70682a497c ("ovl: support idmapped layers") > > > > > Assisted-by: Codex:gpt-5 > > > > > Signed-off-by: Jérémy Jean > > > > > --- ... > > > > > +/* > > > > > + * Lower file handles identify a lower fs, but not the mount whose idmap was > > > > > + * used to decode them. Remember the first lower idmap seen for each fs so > > > > > + * decodable export handles can be disabled if another one appears. > > > > > > I find this behavior counterintuitive. Shouldn't we just fail the > > > mount then? > > > > I would love to fail the mount if you confirm that setting up an ovl > > with several > > lower layers some on the same fs with different idmap, is a non-feature. > > > > I don't know can't /home/amir and /home/brauner be on the same fs with > > different idmapping? > > > > Could it ever make sense to compose an overlay from two such > > directories? > > If not then I would gladly remove this setup from the test matrix. > > > > Thanks, > > Amir. > > Hello, > > I'm digging this up: should I investigate to prepare a new version that > simply fails the mount? Yes, please. Thanks, Amir.