Re: [PATCH] pci: endpoint: functions: Add a virtnet EP function

[Jason Wang <jasowang@redhat.com>]

On 2019/8/24 上午5:31, Haotian Wang wrote:
> This endpoint function enables the PCI endpoint to establish a virtual
> ethernet link with the PCI host. The main features are:
>
> - Zero modification of PCI host kernel. The only requirement for the
>   PCI host is to enable virtio, virtio_pci, virtio_pci_legacy and
>   virito_net.
>
> - The virtual ethernet link is stable enough to support ordinary
>   capabilities of the Linux network stack. User space programs such as
>   ping, ssh, iperf and scp can run on the link without additional
>   hassle.
>
> - This function fits in the PCI endpoint framework
>   (drivers/pci/endpoint/) and makes API calls provided by virtio_net
>   (drivers/net/virtio_net.c). It does not depend on
>   architecture-specific or hardware-specific features.
>
> This function driver is tested on the following pair of systems. The PCI
> endpoint is a Xilinx VCU118 board programmed with a SiFive Linux-capable
> core running Linux 5.2. The PCI host is an x86_64 Intel(R) Core(TM)
> i3-6100 running unmodified Linux 5.2. The virtual link achieved a
> stable throughput of ~180KB/s during scp sessions of a 50M file. The
> PCI host could setup ip-forwarding and NAT to enable the PCI endpoint to
> have Internet access. Documentation for using this function driver is at
> Documentation/PCI/endpoint/pci-epf-virtio-howto.rst.
>
> Reference Docs,
> - Documentation/PCI/endpoint/pci-endpoint.rst. Initialization and
>   removal of endpoint function device and driver.
> - Documentation/PCI/endpoint/pci-endpoint-cfs.rst. Use configfs to
>   control bind, linkup and unbind behavior.
> - https://docs.oasis-open.org/virtio/virtio/v1.1/csprd01/virtio-v1.1-
>   csprd01.html, drivers/virtio/ and drivers/net/virtio_net.c. Algorithms
>   and data structures used by the virtio framework.


Interesting work, several questions:

- Is there a doc for this endpoint device?
- You refer virtio specification in the above, does it mean your device
is fully compatible with virtio (or only datapath is compatible?)
- What's the reason for introducing kthreads for some kinds of
translation or copying of descriptor?
- Is it possible to reuse e.g vringh (by introducing new accesor) and
virtio core codes?


Btw, I'm going to post mdev transport for virtio (with a sample of
vringh loopback device). Technically, this can go through mdev bus as well.

Thanks