An example of how to retrieve XDP hints/metadata from an XDP frame. To
get the xdp_hints struct, one can use:
$ bpftool net xdp show
xdp:
enp6s0(2) md_btf_id(44) md_btf_enabled(0)
To get the BTF id, and then:
$ bpftool btf dump id 44 format c > btf.h
But, in this example, to demonstrate BTF and CORE features, a simpler
struct was defined, containing the only field used by the sample.
A lowpoint is that it's not currently possible to use some CORE features
from "samples/bpf" directory, as those samples are currently built
without using "clang -target bpf". This way, it was not possible to use
"bpf_core_field_exists" macro to check, in runtime, the presence of a
given XDP hints field.
---
samples/bpf/xdp_sample_pkts_kern.c | 21 +++++++++++++++++++++
samples/bpf/xdp_sample_pkts_user.c | 4 +++-
2 files changed, 24 insertions(+), 1 deletion(-)
diff --git a/samples/bpf/xdp_sample_pkts_kern.c b/samples/bpf/xdp_sample_pkts_kern.c
index 9cf76b340dd7..9f0b0c5a6237 100644
--- a/samples/bpf/xdp_sample_pkts_kern.c
+++ b/samples/bpf/xdp_sample_pkts_kern.c
@@ -3,6 +3,7 @@
#include <linux/version.h>
#include <uapi/linux/bpf.h>
#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_core_read.h>
#define SAMPLE_SIZE 64ul
@@ -12,16 +13,23 @@ struct {
__uint(value_size, sizeof(u32));
} my_map SEC(".maps");
+struct xdp_hints {
+ u64 rx_timestamp;
+};
+
SEC("xdp_sample")
int xdp_sample_prog(struct xdp_md *ctx)
{
+ void *meta_data = (void *)(long)ctx->data_meta;
void *data_end = (void *)(long)ctx->data_end;
void *data = (void *)(long)ctx->data;
+ struct xdp_hints *hints;
/* Metadata will be in the perf event before the packet data. */
struct S {
u16 cookie;
u16 pkt_len;
+ u64 rx_timestamp;
} __packed metadata;
if (data < data_end) {
@@ -41,9 +49,22 @@ int xdp_sample_prog(struct xdp_md *ctx)
metadata.cookie = 0xdead;
metadata.pkt_len = (u16)(data_end - data);
+ metadata.rx_timestamp = 0;
sample_size = min(metadata.pkt_len, SAMPLE_SIZE);
flags |= (u64)sample_size << 32;
+ if (meta_data < data) {
+ hints = meta_data;
+ /* bpf_core_field_exists doesn't work from samples/bpf,
+ * as it is only available for "clang -target bpf", which
+ * is not used on samples/bpf. A program that can use
+ * the "vmlinux.h" and "clang -target btf" could use this
+ * call to check the existence of a given field in runtime
+ */
+ /*if (bpf_core_field_exists(hints->rx_timestamp))*/
+ metadata.rx_timestamp = BPF_CORE_READ(hints, rx_timestamp);
+ }
+
ret = bpf_perf_event_output(ctx, &my_map, flags,
&metadata, sizeof(metadata));
if (ret)
diff --git a/samples/bpf/xdp_sample_pkts_user.c b/samples/bpf/xdp_sample_pkts_user.c
index 495e09897bd3..b87e0ae8eb3d 100644
--- a/samples/bpf/xdp_sample_pkts_user.c
+++ b/samples/bpf/xdp_sample_pkts_user.c
@@ -76,6 +76,7 @@ static void print_bpf_output(void *ctx, int cpu, void *data, __u32 size)
struct {
__u16 cookie;
__u16 pkt_len;
+ __u64 rx_timestamp;
__u8 pkt_data[SAMPLE_SIZE];
} __packed *e = data;
int i;
@@ -85,7 +86,8 @@ static void print_bpf_output(void *ctx, int cpu, void *data, __u32 size)
return;
}
- printf("Pkt len: %-5d bytes. Ethernet hdr: ", e->pkt_len);
+ printf("Pkt len: %-5d bytes. RX timestamp: %llu Ethernet hdr: ", e->pkt_len,
+ e->rx_timestamp);
for (i = 0; i < 14 && i < e->pkt_len; i++)
printf("%02x ", e->pkt_data[i]);
printf("\n");
--
2.32.0
