Re: [virtio-comment] Re: [PATCH] Introduce virtio virtual device and transport vq

[Jason Wang <jasowang@redhat.com>]

å 2022/7/12 18:39, Zhu, Lingshan åé:
> > > struct mgmt_dev_avail_res{}, if min_vdev_vqs == max_vdev_vqs, means 
> > > the management device
> > > only supports creating virtual devices with fixed capabilities, this 
> > > kind of virtual devices
> > > can be pre-created. Like the slab allocator, vendors can pre-create 
> > > the device. Then when the management
> > > device receiving the VDEV_CREATE command, it can just pick up a 
> > > free virtual device, and return the
> > > virtual device.
> > So the question still remains, how could we discover those pre-created
> > devices? (having something like initial_vfs?)
> I think for the management devices, pre-creation could be pre-allocated
> hw resource. The management device could pre-allocate a certain number of
> "standard" managed devices, when receive a create command, the management
> device can pick a free managed device, assign an UUID to it, then return
> to the management driver. So the driver may not be aware of this 
> pre-creation,
> it just sees the device is created rapidly. Just like the slab system, 
> or a threads pool.


So for "pre-creating" I meant from the driver perspective. What you 
describe here is invisible to driver. So we don't need a dedicate 
feature in this case.

Btw, I think we need a command to support virtqueue reset in the next 
version.

Thanks


> > > The bit only makes sense for the case when some managed(virtual)
> > > devices are pre-created like initial_vfs in SR-IOV. If we allow
> > > pre-creation, we need commands to discover them.
> > >
> > > I think we need the feature bit VIRTIO_F_TRNSPT_VQ_VDEV, this 
> > > feature bit indicates that the transport
> > > virtqueue is the transport layer for the virtual devices, like PCI 
> > > for a virtio PCI hardware.
> > > So, not only create, we use the transport virtqueue to config the 
> > > device as well.
> > >
> > > And if the virtual devices are pre-created, we can just send the 
> > > create command, and the management device
> > > can find a available device for us, this is also discovery.
> > This seems to conflict with the semantics of pre-created devices.
> same to the above