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[34.79.100.158]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3912c0e2f4fsm20260383f8f.77.2025.03.12.01.34.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 12 Mar 2025 01:34:30 -0700 (PDT) Date: Wed, 12 Mar 2025 08:34:25 +0000 From: Brendan Jackman To: David Hildenbrand Cc: Lorenzo Stoakes , Andrew Morton , Shuah Khan , Dev Jain , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 08/10] selftests/mm: Skip gup_longerm tests on weird filesystems Message-ID: References: <20250228-mm-selftests-v3-0-958e3b6f0203@google.com> <20250228-mm-selftests-v3-8-958e3b6f0203@google.com> <08023d47-dcf4-4efb-bf13-5aef3c6dca14@redhat.com> <16023193-6cb4-46d1-91c4-43342e7e6d30@redhat.com> <41923b80-55f4-44b6-bc59-60327e5308f4@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <41923b80-55f4-44b6-bc59-60327e5308f4@redhat.com> On Tue, Mar 11, 2025 at 08:53:02PM +0100, David Hildenbrand wrote: > > 2. 9pfs seems to pass the f_type through from the host. So you can't > > detect it this way anyway. > > > > [3. I guess overlayfs & friends would also be an issue here although > > that doesn't affect my usecase.] > > > > Anyway, I think we would have to scrape /proc/mounts to do this :( > > > > The question I am asking myself: is this a 9pfs design bug or is it a 9pfs > hypervisor bug. Because we shouldn't try too hard to work around hypervisor > bugs. > > Which 9pfs implementation are you using in the hypervisor? I'm using QEMU via virtme-ng. IIUC virtme-ng knows how to use viortfs for the rootfs, but for individually-mounted directories with --rwdir/--rodir it uses 9pfs unconditionally. Even if it's a bug in QEMU, I think it is worth working around this one way or another. QEMU by far the most practical way to run these tests, and virtme-ng is probably the most popular/practical way to do that. I think even if we are confident it's just a bunch of broken code that isn't even in Linux, it's pragmatic to spend a certain amount of energy on having green tests there. (Also, this f_type thing might be totally intentional specified filesystem behaviour, I don't know).