On Mon, Sep 29, 2025 at 09:22:02AM +0100, Daniel P. Berrangé wrote: > On Mon, Sep 22, 2025 at 04:14:55PM +0100, Alex Bennée wrote: > > "Michael S. Tsirkin" <[email protected]> writes: > > > > > On Mon, Sep 22, 2025 at 03:26:23PM +0200, Christian Speich wrote: > > >> On Mon, Sep 22, 2025 at 09:08:47AM -0400, Michael S. Tsirkin wrote: > > >> > On Mon, Sep 22, 2025 at 01:49:55PM +0100, Daniel P. Berrangé wrote: > > >> > > On Mon, Sep 22, 2025 at 08:15:20AM -0400, Michael S. Tsirkin wrote: > > >> > > > On Mon, Sep 22, 2025 at 12:33:26PM +0100, Daniel P. Berrangé wrote: > > >> > > > > 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. > > >> > > > > > > > > >> > > > > > > [1]: 6275989647efb708f126eb4f880e593792301ed4 > > >> > > > > > > > > >> > > > > > > Signed-off-by: Christian Speich <[email protected]> > > >> > > > > > > --- > > >> > > > > > > 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. > > >> > > > > > > > > >> > > > > > > The reason given is to prevent user confusion. Searching > > >> > > > > > > qemu-discuss or > > >> > > > > > > google for "vhost-user-device" I've seen no confused users. > > >> > > > > > > > > >> > > > > > > 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. > > >> > > > > > > > > >> > > > > > > So I want to propose lifting this restriction to make this > > >> > > > > > > feature > > >> > > > > > > usable without a custom QEMU. > > >> > > > > > > > > >> > > > > > > [1]: 6275989647efb708f126eb4f880e593792301ed4 > > >> > > > > > > > >> > > > > > 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. > > >> > > > > > > > >> > > > > > > > >> > > > > > 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. > > >> > > > > > >> > > > Maybe with the insecure tag you are working on? > > >> > > > > >> > > Sure. > > >> > > > > >> > > > And disable in the default config? > > >> > > > > >> > > Disabling in default config would retain the very problem that > > >> > > Christian > > >> > > is trying to solve - that no distro would have the functionality > > >> > > available > > >> > > for users. > > >> > > > >> > I think his problem is that he has to patch qemu. > > >> > > >> Yes I'm trying to avoid that. Patching qemu also involes providing > > >> updates > > >> (and security patches!) for it. This is a very high burden to turn this > > >> simple flag on. > > >> > > >> > > > >> > As described, this is a developer option not an end user one. > > >> > > >> I don't really get the distintion between developer and end user here. > > >> > > >> As a developer I'm an end user too, I'm concerned with the linux kernel > > >> and the additional host tooling for mac80211_hwsim support but QEMU > > >> I'm just using as an user. > > >> > > > Are you ok with building qemu with an extra config flag? > > > > In my patch I gated the feature on: > > > > VHOST_USER_TEST > > > > so it's easy to patch out of the default config. > > FWIW, we have multiple other test devices that we don't gate behind KConfig > build flags - hyperv-testdev, pc-testdev, pci-testdev & edu.
Well that's because e.g. kvmtest actually depends on pci-testdev. IOW it's actually supported. > IMHO the > vhost user device is more compelling to have enabled by default as it can > actually be used todo something useful. > > IMHO the rationale for disabling it is more fitting to downstreams like > RHEL. > > With regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
