On Mon, Sep 22, 2025 at 06:56:31AM -0400, Michael S. Tsirkin wrote:
> On Mon, Sep 22, 2025 at 12:40:33PM +0200, Christian Speich 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.
> >
> > Thanks for clarifciation, In our use-case we use mac80211_hwsim which is
> > in linux upstream (with the ID 29). So I think a potential reuse here
> > is something that linux upstream already deals with.
>
> So just allow that one?
That would solve our problem.
However, I'm finding it somwhat odd to artifically force the user only use
QEMU it the "allowed way". I'd much rather see that virtio-user-device is
usuable as is (and mac80211_hwsim is not a special case and just works).
Regards,
Christian
>
> > >
> > >
> > > 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.
> >
> > I understand this desire, I'm not sure how this relates with the ability
> > to let a user create a vhost-user-device or not.
> >
> > Kind Regards,
> > Christian
> >
> > >
> > >
> > > > ---
> > > > docs/system/devices/vhost-user.rst | 10 ----------
> > > > hw/virtio/vhost-user-device-pci.c | 3 ---
> > > > hw/virtio/vhost-user-device.c | 3 ---
> > > > 3 files changed, 16 deletions(-)
> > > >
> > > > diff --git a/docs/system/devices/vhost-user.rst
> > > > b/docs/system/devices/vhost-user.rst
> > > > index
> > > > 35259d8ec7c666aa0c56497b8261f48d77216ad5..2d130f9767dbb1cbb85cef43c63dc9a8d7b30d4a
> > > > 100644
> > > > --- a/docs/system/devices/vhost-user.rst
> > > > +++ b/docs/system/devices/vhost-user.rst
> > > > @@ -73,16 +73,6 @@ all the required parameters including:
> > > > - The ``num_vqs`` it needs and their ``vq_size``
> > > > - The ``config_size`` if needed
> > > >
> > > > -.. note::
> > > > - To prevent user confusion you cannot currently instantiate
> > > > - vhost-user-device without first patching out::
> > > > -
> > > > - /* Reason: stop inexperienced users confusing themselves */
> > > > - dc->user_creatable = false;
> > > > -
> > > > - in ``vhost-user-device.c`` and ``vhost-user-device-pci.c`` file and
> > > > - rebuilding.
> > > > -
> > > > vhost-user daemon
> > > > =================
> > > >
> > > > diff --git a/hw/virtio/vhost-user-device-pci.c
> > > > b/hw/virtio/vhost-user-device-pci.c
> > > > index
> > > > f10bac874e78429c633752a4ce9db28385b3bb07..c76a856c9b9a67d941a93929244216658ff2a156
> > > > 100644
> > > > --- a/hw/virtio/vhost-user-device-pci.c
> > > > +++ b/hw/virtio/vhost-user-device-pci.c
> > > > @@ -38,9 +38,6 @@ static void
> > > > vhost_user_device_pci_class_init(ObjectClass *klass,
> > > > VirtioPCIClass *k = VIRTIO_PCI_CLASS(klass);
> > > > PCIDeviceClass *pcidev_k = PCI_DEVICE_CLASS(klass);
> > > >
> > > > - /* Reason: stop users confusing themselves */
> > > > - dc->user_creatable = false;
> > > > -
> > > > k->realize = vhost_user_device_pci_realize;
> > > > set_bit(DEVICE_CATEGORY_INPUT, dc->categories);
> > > > pcidev_k->vendor_id = PCI_VENDOR_ID_REDHAT_QUMRANET;
> > > > diff --git a/hw/virtio/vhost-user-device.c
> > > > b/hw/virtio/vhost-user-device.c
> > > > index
> > > > 3939bdf755222a281da8ca22243d7d4f16990a66..1bea496afd0137ba9b42009f6252acf6800528d1
> > > > 100644
> > > > --- a/hw/virtio/vhost-user-device.c
> > > > +++ b/hw/virtio/vhost-user-device.c
> > > > @@ -41,9 +41,6 @@ static void vud_class_init(ObjectClass *klass, const
> > > > void *data)
> > > > {
> > > > DeviceClass *dc = DEVICE_CLASS(klass);
> > > >
> > > > - /* Reason: stop inexperienced users confusing themselves */
> > > > - dc->user_creatable = false;
> > > > -
> > > > device_class_set_props(dc, vud_properties);
> > > > dc->vmsd = &vud_vmstate;
> > > > set_bit(DEVICE_CATEGORY_INPUT, dc->categories);
> > > >
> > > > ---
> > > > base-commit: e7c1e8043a69c5a8efa39d4f9d111f7c72c076e6
> > > > change-id: 20250919-vhost-user-device-creatable-b7f9b7b5bfb2
> > > >
> > > > Best regards,
> > > > --
> > > > Christian Speich <[email protected]>
> > >
> > >
>
>
