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.
> ---
> 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]>
