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SubjectRe: [RFC v2] vhost: introduce mdev based hardware vhost backend
On Wed,  3 Jul 2019 17:13:39 +0800
Tiwei Bie <tiwei.bie@intel.com> wrote:
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 8f10748dac79..6c5718ab7eeb 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -201,6 +201,7 @@ struct vfio_device_info {
> #define VFIO_DEVICE_FLAGS_AMBA (1 << 3) /* vfio-amba device */
> #define VFIO_DEVICE_FLAGS_CCW (1 << 4) /* vfio-ccw device */
> #define VFIO_DEVICE_FLAGS_AP (1 << 5) /* vfio-ap device */
> +#define VFIO_DEVICE_FLAGS_VHOST (1 << 6) /* vfio-vhost device */
> __u32 num_regions; /* Max region index + 1 */
> __u32 num_irqs; /* Max IRQ index + 1 */
> };
> @@ -217,6 +218,7 @@ struct vfio_device_info {
> #define VFIO_DEVICE_API_AMBA_STRING "vfio-amba"
> #define VFIO_DEVICE_API_CCW_STRING "vfio-ccw"
> #define VFIO_DEVICE_API_AP_STRING "vfio-ap"
> +#define VFIO_DEVICE_API_VHOST_STRING "vfio-vhost"
>
> /**
> * VFIO_DEVICE_GET_REGION_INFO - _IOWR(VFIO_TYPE, VFIO_BASE + 8,
> @@ -573,6 +575,23 @@ enum {
> VFIO_CCW_NUM_IRQS
> };
>
> +/*
> + * The vfio-vhost bus driver makes use of the following fixed region and
> + * IRQ index mapping. Unimplemented regions return a size of zero.
> + * Unimplemented IRQ types return a count of zero.
> + */
> +
> +enum {
> + VFIO_VHOST_CONFIG_REGION_INDEX,
> + VFIO_VHOST_NOTIFY_REGION_INDEX,
> + VFIO_VHOST_NUM_REGIONS
> +};
> +
> +enum {
> + VFIO_VHOST_VQ_IRQ_INDEX,
> + VFIO_VHOST_NUM_IRQS
> +};
> +

Note that the vfio API has evolved a bit since vfio-pci started this
way, with fixed indexes for pre-defined region types. We now support
device specific regions which can be identified by a capability within
the REGION_INFO ioctl return data. This allows a bit more flexibility,
at the cost of complexity, but the infrastructure already exists in
kernel and QEMU to make it relatively easy. I think we'll have the
same support for interrupts soon too. If you continue to pursue the
vfio-vhost direction you might want to consider these before committing
to fixed indexes. Thanks,

Alex

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