Re: [PATCH v11 5/5] docs: Add generic vhost-vdpa device documentation

[Jason Wang]

On Thu, Dec 15, 2022 at 9:50 PM Longpeng(Mike) <longpeng2@huawei.com> wrote:
>
> From: Longpeng <longpeng2@huawei.com>
>
> Signed-off-by: Longpeng <longpeng2@huawei.com>
> ---
>  .../devices/vhost-vdpa-generic-device.rst     | 68 +++++++++++++++++++
>  1 file changed, 68 insertions(+)
>  create mode 100644 docs/system/devices/vhost-vdpa-generic-device.rst
>
> diff --git a/docs/system/devices/vhost-vdpa-generic-device.rst 
> b/docs/system/devices/vhost-vdpa-generic-device.rst
> new file mode 100644
> index 0000000000..24c825ef1a
> --- /dev/null
> +++ b/docs/system/devices/vhost-vdpa-generic-device.rst
> @@ -0,0 +1,68 @@
> +
> +=========================
> +vhost-vDPA generic device
> +=========================
> +
> +This document explains the usage of the vhost-vDPA generic device.
> +
> +
> +Description
> +-----------
> +
> +vDPA(virtio data path acceleration) device is a device that uses a datapath
> +which complies with the virtio specifications with vendor specific control
> +path.
> +
> +QEMU provides two types of vhost-vDPA devices to enable the vDPA device, one
> +is type sensitive which means QEMU needs to know the actual device type
> +(e.g. net, blk, scsi) and another is called "vhost-vDPA generic device" which
> +is type insensitive.
> +
> +The vhost-vDPA generic device builds on the vhost-vdpa subsystem and virtio
> +subsystem. It is quite small, but it can support any type of virtio device.
> +
> +
> +Requirements
> +------------
> +Linux 5.18+
> +iproute2/vdpa 5.12.0+
> +
> +
> +Examples
> +--------
> +
> +1. Prepare the vhost-vDPA backends, here is an example using vdpa_sim_blk
> +   device:
> +
> +::
> +  host# modprobe vhost_vdpa
> +  host# modprobe vdpa_sim_blk

Nit: it's probably better to add driver binding steps here.

> +  host# vdpa dev add mgmtdev vdpasim_blk name blk0
> +  (...you can see the vhost-vDPA device under /dev directory now...)

And then the vhost char dev name could be fetch via

ls /sys/bus/vdpa/device/blk0/vhost-vdpa*

With the above changes.

Acked-by: Jason Wang <jasowang@redhat.com>

Thanks

> +  host# ls -l /dev/vhost-vdpa-*
> +  crw------- 1 root root 236, 0 Nov  2 00:49 /dev/vhost-vdpa-0
> +
> +Note:
> +It needs some vendor-specific steps to provision the vDPA device if you're
> +using real HW devices, such as loading the vendor-specific vDPA driver and
> +binding the device to the driver.
> +
> +
> +2. Start the virtual machine:
> +
> +Start QEMU with virtio-mmio bus:
> +
> +::
> +  host# qemu-system                                                  \
> +      -M microvm -m 512 -smp 2 -kernel ... -initrd ...               \
> +      -device vhost-vdpa-device,vhostdev=/dev/vhost-vdpa-0           \
> +      ...
> +
> +
> +Start QEMU with virtio-pci bus:
> +
> +::
> +  host# qemu-system                                                  \
> +      -M pc -m 512 -smp 2                                            \
> +      -device vhost-vdpa-device-pci,vhostdev=/dev/vhost-vdpa-0       \
> +      ...
> --
> 2.23.0
>