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[178.84.201.199]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c5095b41f44sm206223866b.31.2026.11.14.03.55.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 14 Nov 2026 03:55:36 -0800 (PST) Date: Sat, 14 Nov 2026 12:55:35 +0100 From: Amir Goldstein To: Alexander Mikhalitsyn Cc: Christoph Hellwig , Christian Brauner , linux-fsdevel@vger.kernel.org, Jann Horn , Chris Mason , Josef Bacik , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, Alexander Viro , Jan Kara , linux-scsi@vger.kernel.org, target-devel@vger.kernel.org, driver-core@lists.linux.dev, linux-mm@kvack.org, bpf@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, apparmor@lists.ubuntu.com, linux-nfs@vger.kernel.org, netdev@vger.kernel.org, fuse-devel@lists.linux.dev, linux-efi@vger.kernel.org, xen-devel@lists.xenproject.org, ocfs2-devel@lists.linux.dev, linux-s390@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-usb@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH RFC 38/41] fuse: refuse files on pseudo filesystems as passthrough backing files Message-ID: References: <20261110-work-loop-pseudo-v1-0-4c998976c6c7@kernel.org> <20261110-work-loop-pseudo-v1-38-4c998976c6c7@kernel.org> <20261111151202.GA11391@lst.de> X-Mailing-List: bpf@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=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Fri, Nov 13, 2026 at 11:25:57AM +0100, Alexander Mikhalitsyn wrote: > Hi Christoph, > > On Wed, 2026-11-11 at 16:12 +0100, Christoph Hellwig wrote: > > I've seen setups where people use fuse to mediate access to sysfs > > sysfs in odd ways.  No idea if that's still around, but if so, this > > patch will break it. > > > Oh, that's painful. Do they use backing files for that? > It's a relatively new feature in FUSE... > Very unlikely that they use FUSE passthrough and if they did very unlikely that it would break their filesystem. The API for fuse passthrough is that the server requests to setup a backing file before open via ioctl and if ioctl fails (as this patch does) then server falls back to non-passthrough open. The ioctl can already fail for many reasons such as MAX_STACK_DEPTH on procfs as the commit message says, so server needs to cope with the fall back. Thanks, Amir.