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

[Michael S. Tsirkin]

On Fri, Dec 16, 2022 at 11:33:49AM +0800, Jason Wang wrote:
> 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


Sounds minor enough, I'll queue, pls fix with a patch on top.

> > +  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
> >