Re: [dpdk-dev] [PATCH 1/3] kcp: add kernel control path kernel module

[Avi Kivity <avi@scylladb.com>]

On 02/28/2016 10:16 PM, Ferruh Yigit wrote:
> On 2/28/2016 3:34 PM, Avi Kivity wrote:
>> On 01/27/2016 06:24 PM, Ferruh Yigit wrote:
>>> This kernel module is based on KNI module, but this one is stripped
>>> version of it and only for control messages, no data transfer
>>> functionality provided.
>>>
>>> This Linux kernel module helps userspace application create virtual
>>> interfaces and when a control command issued into that virtual
>>> interface, module pushes the command to the userspace and gets the
>>> response back for the caller application.
>>>
>>> The Linux tools like ethtool/ifconfig/ip can be used on virtual
>>> interfaces but not ones for related data, like tcpdump.
>>>
>>> In long term this patch intends to replace the KNI and KNI will be
>>> depreciated.
>> Instead of adding yet another out-of-tree kernel module, why not extend
>> the existing in-tree tap driver?  This will make everyone's life easier.
>>
>> Since tap also supports data transfer, an application can also forward
>> packets not intended to it to the kernel, and forward packets from the
>> kernel through the device.
>>
> Hi Avi,
>
> KDP (Kernel Data Path) does what you have described, it is implemented
> as PMD and it benefits from tap driver to data transfer through the
> kernel. It also support custom kernel module for better performance.
>
> For KCP (Kernel Control Path), network driver forwards control commands
> to the userspace driver, I doubt this is something wanted for tun/tap
> driver, so extending tun/tap driver like this can be hard to upstream.

Have you tried asking?  Maybe if you explain it they will be open to the 
extension.

Certainly it will be better to have KCP and KDP use the same kernel 
interface name; so we'll need to either add data path support to kcp 
(causing duplication with tap), or add control path support to tap. I 
think the latter is preferable.

> We are investigating about adding a native support to Linux kernel for
> KCP, but there is no task started for this right now, any support is
> welcome.
>
>