This patch set improves the documentation and selftests for XDP Rx metadata handling. The first patch clarifies the documentation around XDP metadata layout and the use of bpf_xdp_adjust_meta. The second patch enhances the BPF selftests to make XDP metadata handling more robust and portable across different NICs.
Prior to this patch set, the user application retrieved the xdp_meta by calculating backward from the data pointer, while the XDP program fill in the xdp_meta by calculating backward from data_meta. This approach will cause mismatch if there is device-reserved metadata.
|<---sizeof(xdp_meta)--| | | struct xdp_meta rx_desc->address ^ ^ | | +----------+----------------------+------------+------+ | headroom | custom metadata | reserved | data | +----------+----------------------+------------+------+ ^ ^ ^ | | | struct xdp_meta xdp_buff->data_meta xdp_buff->data | | |<---sizeof(xdp_meta)--|
V2: - unconditionally do bpf_xdp_adjust_meta with -XDP_METADATA_SIZE (Stanislav)
V1: https://lore.kernel.org/netdev/20250701042940.3272325-1-yoong.siang.song@int...
Song Yoong Siang (2): doc: clarify XDP Rx metadata layout and bpf_xdp_adjust_meta usage selftests/bpf: Enhance XDP Rx Metadata Handling
Documentation/networking/xdp-rx-metadata.rst | 38 +++++++++++++++++++ .../selftests/bpf/prog_tests/xdp_metadata.c | 2 +- .../selftests/bpf/progs/xdp_hw_metadata.c | 2 +- .../selftests/bpf/progs/xdp_metadata.c | 2 +- tools/testing/selftests/bpf/xdp_hw_metadata.c | 2 +- tools/testing/selftests/bpf/xdp_metadata.h | 7 ++++ 6 files changed, 49 insertions(+), 4 deletions(-)