On Fri, Feb 14, 2020 at 11:23:27AM +0800, Jason Wang wrote: > > > Though all vDPA devices have the same programming interface, but the > > > semantic is different. So it looks to me that use bus complies what > > > class.rst said: > > > > > > " > > > > > > Each device class defines a set of semantics and a programming interface > > > that devices of that class adhere to. Device drivers are the > > > implementation of that programming interface for a particular device on > > > a particular bus. > > > > > > " > > Here we are talking about the /dev/XX node that provides the > > programming interface. > > > I'm confused here, are you suggesting to use class to create char device in > vhost-vdpa? That's fine but the comment should go for vhost-vdpa patch. Certainly yes, something creating many char devs should have a class. That makes the sysfs work as expected I suppose this is vhost user? I admit I don't really see how this vhost stuff works, all I see are global misc devices? Very unusual for a new subsystem to be using global misc devices.. I would have expected that a single VDPA device comes out as a single char dev linked to only that VDPA device. > > All the vdpa devices have the same basic > > chardev interface and discover any semantic variations 'in band' > > That's not true, char interface is only used for vhost. Kernel virtio driver > does not need char dev but a device on the virtio bus. Okay, this is fine, but why do you need two busses to accomplish this? Shouldn't the 'struct virito_device' be the plug in point for HW drivers I was talking about - and from there a vhost-user can connect to the struct virtio_device to give it a char dev or a kernel driver can connect to link it to another subsystem? It is easy to see something is going wrong with this design because the drivers/virtio/virtio_vdpa.c mainly contains a bunch of trampoline functions reflecting identical calls from one ops struct to a different ops struct. This suggests the 'vdpa' is some subclass of 'virtio' and it is possibly better to model it by extending 'struct virito_device' to include the vdpa specific stuff. Where does the vhost-user char dev get invovled in with the v2 series? Is that included? > > Every class of virtio traffic is going to need a special HW driver to > > enable VDPA, that special driver can create the correct vhost side > > class device. > > Are you saying, e.g it's the charge of IFCVF driver to create vhost char dev > and other stuffs? No. Jason
