On Mon, 25 Aug 2025 12:39:11 -0700 Amery Hung wrote:

Hi all,

This patchset introduces a new kfunc bpf_xdp_pull_data() to allow
pulling nonlinear xdp data. This may be useful when a driver places
headers in fragments. When an xdp program would like to keep parsing
packet headers using direct packet access, it can call
bpf_xdp_pull_data() to make the header available in the linear data
area. The kfunc can also be used to decapsulate the header in the
nonlinear data, as currently there is no easy way to do this.

This patchset also tries to fix an issue in the mlx5e driver. The driver
curretly assumes the packet layout to be unchanged after xdp program
runs and may generate packet with corrupted data or trigger kernel warning
if xdp programs calls layout-changing kfunc such as bpf_xdp_adjust_tail(),
bpf_xdp_adjust_head() or bpf_xdp_pull_data() introduced in this set.

Tested with the added bpf selftest using bpf test_run and also on
mlx5e with the tools/testing/selftests/drivers/net/xdp.py. mlx5e with
striding RQ will produce xdp_buff with empty linear data.
xdp.test_xdp_native_pass_mb would fail to parse the header before this
patchset.

Grateful for any feedback (especially the driver part).

CC: Gal, this is the correct way to resolve the XDP not having headers
in the first frag for mlx5.