On Mon, Sep 22, 2025 at 03:33:59PM +0200, Christian Speich 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 <c.spe...@avm.de> > > > > --- > > > > 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. > > I don't mind the 'x-'. And if that makes it clear, that this is used > without any warrenty, sure! > > However I'm not sure where the "risky" comes from. Initially confusion > was given as reason.
I view it as "risky" in two ways - this device makes it very easy for a user to shoot themselves in the foot - we dont want to have to think about compatibility across QEMU releases in case there is something peculiar about a particular device type. IMHO, adding the 'x-' prefix and disclaiming full support is sufficient mitigation. > Initially I thought about some kind of '--i-really-want-to-do-this' > flag, but somehow I don't really see this device to bethis harmful > to to warrent that big of a deterrent. I agree. 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 :|
