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Tsirkin" , Christian Speich , qemu-devel@nongnu.org, Stefano Garzarella Subject: Re: [PATCH] virtio: vhost-user-device: Make user creatable again In-Reply-To: ("Daniel P. =?utf-8?Q?Berrang?= =?utf-8?Q?=C3=A9=22's?= message of "Mon, 22 Sep 2025 12:33:26 +0100") References: <20250919-vhost-user-device-creatable-v1-1-87eefeea7f68@avm.de> <20250919160526-mutt-send-email-mst@kernel.org> User-Agent: mu4e 1.12.12; emacs 30.1 Date: Mon, 22 Sep 2025 13:51:36 +0100 Message-ID: <87frceodk7.fsf@draig.linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=2a00:1450:4864:20::332; envelope-from=alex.bennee@linaro.org; helo=mail-wm1-x332.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Daniel P. Berrang=C3=A9 writes: > On Fri, Sep 19, 2025 at 04:07:19PM -0400, Michael S. Tsirkin wrote: >> On Fri, Sep 19, 2025 at 04:30:53PM +0200, Christian Speich wrote: >> > This removes the change introduced in [1] that prevents the use of >> > vhost-user-device and vhost-user-device-pci on unpatched QEMU builds. >> >=20 >> > [1]: 6275989647efb708f126eb4f880e593792301ed4 >> >=20 >> > Signed-off-by: Christian Speich >> > --- >> > vhost-user-device and vhost-user-device-pci started out as user >> > creatable devices. This was changed in [1] when the vhost-user-base was >> > introduced. >> >=20 >> > The reason given is to prevent user confusion. Searching qemu-discuss = or >> > google for "vhost-user-device" I've seen no confused users. >> >=20 >> > Our use case is to provide wifi emulation using "vhost-user-device-pci= ", >> > which currently is working fine with the QEMU 9.0.2 present in Ubuntu >> > 24.04. With newer QEMU versions we now need to patch, distribute and >> > maintain our own QEMU packages, which is non-trivial. >> >=20 >> > So I want to propose lifting this restriction to make this feature >> > usable without a custom QEMU. >> >=20 >> > [1]: 6275989647efb708f126eb4f880e593792301ed4 >>=20 >> The confusion is after someone reuses the ID you are claiming without >> telling anyone and then linux guests will start binding that driver to >> your device. >>=20 >>=20 >> We want people doing this kind of thing to *at a minimum* >> go ahead and register a device id with the virtio TC, >> but really to write and publish a spec. > > Wanting people to register a device ID is a social problem and > we're trying to apply a technical hammer to it, which is rarely > an productive approach. > > If we want to demonstrate that vhost-user-device is "risky", then > how about we rename it to have an 'x-' prefix and thus disclaim > any support for it, but none the less allow its use. Document it > as an experimental device, and if it breaks, users get to keep > both pieces. > > It seems like it would be useful before any virtio spec submission > as a mechanism by which users can experiment to finese their ideas > prior to getting to the point of needing to make a spec proposal. That's basically it. Adding the stubs is fairly trivial for vhost-user backends that implement the config space but you can't add stubs for things that are currently RFC specs. Also you are forcing a delay for the spec to be updated and then wait for the next QEMU with the stub added. > > With regards, > Daniel --=20 Alex Benn=C3=A9e Virtualisation Tech Lead @ Linaro