[RFC] virtio-net: AF_XDP zero-copy TX checksum offload

[Azadeh Aftahi <aftahi334@gmail.com>]

Hi all,

I'm planning to work on single-buffer AF_XDP zero-copy TX checksum offload for virtio-net.

Current net-next's virtnet_xsk_xmit_one() does not consume XSK TX checksum metadata and uses the shared zeroed virtio header.

I found Xuan's 2021 proposal anticipating separate headers for checksum support, and the merged 2024 zero-copy TX series, 
but I couldn't find a checksum-specific follow-up implementation.

The proposed scope is to map the existing XSK checksum metadata API to VIRTIO_NET_F_CSUM, 
using a DMA-safe per-packet virtio header whose lifetime extends until TX completion, with corresponding completion, reset, and unbind cleanup.

I would keep the initial scope limited to single-buffer TX: no multi-buffer RX, timestamps, launch time, or GSO.

I'd also add checksum and header-lifetime coverage using the existing XSK selftest framework with QEMU/TAP.

Is anyone already working on this? If not, does this scope and per-packet-header approach sound reasonable for a follow-up patch?

Thanks,
Azadeh