Re: [dpdk-dev] [RFC PATCH 3/7] lib/librte_vhost: Add an abstraction layer tointerpret messages

[Tetsuya Mukawa <mukawa@igel.co.jp>]

Hi Xie,

(2014/11/08 5:43), Xie, Huawei wrote:
>> -struct vhost_net_device_ops const *get_virtio_net_callbacks(void);
>> +struct vhost_net_device_ops const *get_virtio_net_callbacks(
>> +		vhost_driver_type_t type);
> Tetsuya:
> I feel currently it is better we still keep the common get_virtio_net_callbacks(). 
> For the message flow from control layer 1 (cuse ioctl or user sock message recv/xmit)---> cuse/user local message handling layer 2-> common virtio message handling layer 3
> Layer 1 and layer 2 belong to one  module. It is that module's choice whether to implement callbacks between internal layer1 and layer2. We don't need to force that.
> Besides, even that module wants to define the ops between layer 1 and layer2, the interface could be different between cuse/user. 
> Refer to the following code for user:
>
> vhost-user-server.c:
> case VHOST_USER_SET_MEM_TABLE:
> 	user_set_mem_table(ctx, &msg)
>
> virtio-net-user.c:
> user_set_mem_table(struct vhost_device_ctx ctx, struct VhostUserMsg *pmsg)
> {
>
> ....
>
> 	ops->set_mem_table(ctx, regions, memory.nregions);
> }
>
>
I may misunderstand what you say, please let me know in the case.
I guess it's difficult to remove 'vhost_driver_type_t'  from
'get_virtio_net_callbacks()'.
In original vhost example code, there are 2 layers related with
initialization as you mentioned.
  + Layer1: cuse ioctl handling layer.
  + Layer2: vhost-cuse( = vhost-net) message handling layer.

Layer1 needs function pointers to call Layer2 functions.
'get_virtio_net_callbacks()' is used for that purpose.

My RFC is based on above, but Layer1/2 are abstracted to hide vhost-cuse
and vhost-user.
 + Layer1: device control abstraction layer.
 -- Layer1-a: cuse ioctl handling layer.
 -- Layer1-b: unix domain socket handling layer.
 + Layer2: message handling abstraction layer.
 -- Layer2-a: vhost-cuse(vhost-net) message handling layer.
 -- Layer2-b: vhost-user message handling layer.

Still Layer1 needs function pointers of Layer2.
So, anyway, we still need to implement 'get_virtio_net_callbacks()'.

Also, as you mentioned, function definition and behavior are different
between Layer2-a and Lanyer2-b like 'user_set_mem_table()'.
Because of this, 'get_virtio_net_callbacks()' need to return collect
function pointers to Layer1.
So I guess 'get_virtio_net_callbacks()' needs 'vhost_driver_type_t' to
know which function pointers are needed by Layer1.

If someone wants to implement new vhost-backend, of course they can
implement Layer2 implementation and Layer1 together.
In the case,  they doesn't need to call 'get_virtio_net_callbacks()'.
Also they can reuse existing Layer2 implementation by calling
'get_virtio_net_callbacks()' with existing driver type, or they can
implement a new Layer2 implementation for new vhost-backend.

BTW, the name of 'vhost_driver_type_t' is redundant, I will change the name.

Tetsuya