Subject: [RFC bpf-next 5/5] selftests/bpf: Test rx_timestamp metadata in xskxceiver

From: Stanislav Fomichev <[email-masked]>
Date: Thu, 27 Oct 2022 13:00:19 -0700

Example on how the metadata is prepared from the BPF context
and consumed by AF_XDP:

- bpf_xdp_metadata_have_rx_timestamp to test whether it's supported;
  if not, I'm assuming verifier will remove this "if (0)" branch
- bpf_xdp_metadata_rx_timestamp returns a _copy_ of metadata;
  the program has to bpf_xdp_adjust_meta+memcpy it;
  maybe returning a pointer is better?
- af_xdp consumer grabs it from data-<expected_metadata_offset> and
  makes sure timestamp is not empty
- when loading the program, we pass BPF_F_XDP_HAS_METADATA+prog_ifindex

Cc: Martin KaFai Lau <[email-masked]>
Cc: Jakub Kicinski <[email-masked]>
Cc: Willem de Bruijn <[email-masked]>
Cc: Jesper Dangaard Brouer <[email-masked]>
Cc: Anatoly Burakov <[email-masked]>
Cc: Alexander Lobakin <[email-masked]>
Cc: Magnus Karlsson <[email-masked]>
Cc: Maryam Tahhan <[email-masked]>
Cc: [email-masked]
Cc: [email-masked]
Signed-off-by: Stanislav Fomichev <[email-masked]>
---
 .../testing/selftests/bpf/progs/xskxceiver.c  | 22 ++++++++++++++++++
 tools/testing/selftests/bpf/xskxceiver.c      | 23 ++++++++++++++++++-
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/progs/xskxceiver.c b/tools/testing/selftests/bpf/progs/xskxceiver.c
index b135daddad3a..83c879aa3581 100644
--- a/tools/testing/selftests/bpf/progs/xskxceiver.c
+++ b/tools/testing/selftests/bpf/progs/xskxceiver.c
@@ -12,9 +12,31 @@ struct {
 	__type(value, __u32);
 } xsk SEC(".maps");
 
+extern int bpf_xdp_metadata_have_rx_timestamp(struct xdp_md *ctx) __ksym;
+extern __u32 bpf_xdp_metadata_rx_timestamp(struct xdp_md *ctx) __ksym;
+
 SEC("xdp")
 int rx(struct xdp_md *ctx)
 {
+	void *data, *data_meta;
+	__u32 rx_timestamp;
+	int ret;
+
+	if (bpf_xdp_metadata_have_rx_timestamp(ctx)) {
+		ret = bpf_xdp_adjust_meta(ctx, -(int)sizeof(__u32));
+		if (ret != 0)
+			return XDP_DROP;
+
+		data = (void *)(long)ctx->data;
+		data_meta = (void *)(long)ctx->data_meta;
+
+		if (data_meta + sizeof(__u32) > data)
+			return XDP_DROP;
+
+		rx_timestamp = bpf_xdp_metadata_rx_timestamp(ctx);
+		__builtin_memcpy(data_meta, &rx_timestamp, sizeof(__u32));
+	}
+
 	return bpf_redirect_map(&xsk, ctx->rx_queue_index, XDP_PASS);
 }
 
diff --git a/tools/testing/selftests/bpf/xskxceiver.c b/tools/testing/selftests/bpf/xskxceiver.c
index 066bd691db13..ce82c89a432e 100644
--- a/tools/testing/selftests/bpf/xskxceiver.c
+++ b/tools/testing/selftests/bpf/xskxceiver.c
@@ -871,7 +871,9 @@ static bool is_offset_correct(struct xsk_umem_info *umem, struct pkt_stream *pkt
 static bool is_pkt_valid(struct pkt *pkt, void *buffer, u64 addr, u32 len)
 {
 	void *data = xsk_umem__get_data(buffer, addr);
+	void *data_meta = data - sizeof(__u32);
 	struct iphdr *iphdr = (struct iphdr *)(data + sizeof(struct ethhdr));
+	__u32 rx_timestamp = 0;
 
 	if (!pkt) {
 		ksft_print_msg("[%s] too many packets received\n", __func__);
@@ -907,6 +909,13 @@ static bool is_pkt_valid(struct pkt *pkt, void *buffer, u64 addr, u32 len)
 		return false;
 	}
 
+	memcpy(&rx_timestamp, data_meta, sizeof(rx_timestamp));
+	if (rx_timestamp == 0) {
+		ksft_print_msg("Invalid metadata received: ");
+		ksft_print_msg("got %08x, expected != 0\n", rx_timestamp);
+		return false;
+	}
+
 	return true;
 }
 
@@ -1331,6 +1340,7 @@ static void thread_common_ops(struct test_spec *test, struct ifobject *ifobject)
 	u64 umem_sz = ifobject->umem->num_frames * ifobject->umem->frame_size;
 	int mmap_flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE;
 	LIBBPF_OPTS(bpf_xdp_query_opts, opts);
+	LIBBPF_OPTS(bpf_object_open_opts, open_opts);
 	int ret, ifindex;
 	void *bufs;
 
@@ -1340,10 +1350,21 @@ static void thread_common_ops(struct test_spec *test, struct ifobject *ifobject)
 	if (!ifindex)
 		exit_with_error(errno);
 
-	ifobject->bpf_obj = xskxceiver__open_and_load();
+	open_opts.prog_ifindex = ifindex;
+
+	ifobject->bpf_obj = xskxceiver__open_opts(&open_opts);
 	if (libbpf_get_error(ifobject->bpf_obj))
 		exit_with_error(libbpf_get_error(ifobject->bpf_obj));
 
+	ret = bpf_program__set_flags(bpf_object__find_program_by_name(ifobject->bpf_obj->obj, "rx"),
+				     BPF_F_XDP_HAS_METADATA);
+	if (ret < 0)
+		exit_with_error(ret);
+
+	ret = xskxceiver__load(ifobject->bpf_obj);
+	if (ret < 0)
+		exit_with_error(ret);
+
 	if (ifobject->umem->unaligned_mode)
 		mmap_flags |= MAP_HUGETLB;
 
-- 
2.38.1.273.g43a17bfeac-goog