Re: [PATCH net v4 2/2] selftests/bpf: cover AF_XDP multi-buffer TX software checksum

Extend test_xdp_metadata to send the same UDP packet using every descriptor
count from 1 through MAX_TX_DESCS (MAX_SKB_FRAGS + 1), and to run the
existing metadata and checksum verification for each case.

Build the packet once and write it into the TX descriptors in a loop
instead of using a flat two-descriptor layout. Keep the first descriptor
large enough to cover the checksum offset; the remaining payload is split
across the continuation descriptors, with the last descriptor taking the
remaining length.

Reuse the existing AF_XDP setup, packet generation, completion, and receive
helpers in xdp_metadata.c instead of adding a separate test harness.

Signed-off-by: Rongzheng Wang <redacted>
---
 .../selftests/bpf/prog_tests/xdp_metadata.c   | 147 +++++++++++-------
 1 file changed, 92 insertions(+), 55 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c b/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c
index 5c31054ad4a4..17da0a145666 100644
--- a/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c

@@ -18,12 +18,15 @@
 #define TX_NAME "veTX"
 #define RX_NAME "veRX"
 
-#define UDP_PAYLOAD_BYTES 4
+#define UDP_PAYLOAD_BYTES 32
+