On 02/29/2016 12:43 PM, Ferruh Yigit wrote: > On 2/29/2016 9:43 AM, Avi Kivity wrote: >> 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. >> > Not communicated but tun/tap already doing something different. > For KCP, created interface is map of the DPDK port. All data interface > shows coming from DPDK port. For example if you get stats information > with ifconfig, the values you observe are DPDK port statistics -not > statistics of data between userspace and kernelspace, statistics of data > forwarded between DPDK ports. If you down the interface, DPDK port > stopped, etc... > > If you extend the tun/tap, it won't be map of the DPDK port, and if you > get statistics information from that interface, what do you expect to > see, the data transferred between kernel and userspace, or underlying > DPDK port forwarding statistics?
Good point. But you really have to involve netdev on this, or you'll live out-of-tree forever. > Extending tun/tap in a way we want, forwarding all control commands to > userspace, will break the current tun/tap, this doesn't looks like a > valid option to me. It's possible to enhance it while preserving backwards compatibility, by enabling a feature flag (statistics from userspace). > For data path, using tun/tap is OK and we are already doing it, for the > control path I believe we need a new driver. > >> 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. >> > Why it is better to have same interface? Anyone who is not interested > with kernel data path may want to control DPDK ports using common tools, > or want to get some basic information and stats using ethtool or > ifconfig. Why we need to bind two different functionality together? Having two interfaces will be confusing for the user. If I wish to firewall data packets coming from the dpdk port, do I set firewall rules on dpdk0 or tap0? I don't think it matters whether you extend tap, or add a data path to kcp, but if you want to upstream it, it needs to be blessed by netdev. > >>> 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. >>> >>>
