Re: [Proposal] Relationship between XDP and rx-csum in virtio-net

[Heng Qi <hengqi@linux.alibaba.com>]

On Mon, May 22, 2023 at 03:10:05PM -0400, Michael S. Tsirkin wrote:
> On Mon, May 22, 2023 at 08:12:00PM +0800, Heng Qi wrote:
> > 1) Add a feature bit to the virtio specification to tell the sender that a fully
> > csumed packet must be sent.
> 
> Who is the sender in this picture? The driver?

The device or the driver.

When the device is hw, the sender is more likely to be a device.
When the device is sw, the sender can be a device or a driver.

But in general, this feature is inclined to constrain the behavior of the device and
the driver from the receiving side.

For example: 
VIRTIO_NET_F_UNNECESSARY_CSUM : The driver tells the device that you must send me a fully csumed packet.

Then the specific implementation can be

(1) the sender sends a fully csumed packet;
(2) the receiver receives a CHECKSUM_PARTIAL packet, and the device helps calculate the fully csum
    (because the two parties in the communication are located on the same host, the packet is trusted.).

In summary, if VIRTIO_NET_F_UNNECESSARY_CSUM is negotiated, the driver will no longer receive any packets marked CHECKSUM_PARTIAL.

Thanks.

> 
> -- 
> MST