On Tue, 05 Jun 2018 16:50:00 +0200, Toke Høiland-Jørgensen wrote:
> Add an example program showing how to sample packets from XDP using the
> perf event buffer. The example userspace program just prints the ethernet
> header for every packet sampled.
>
> Signed-off-by: Toke Høiland-Jørgensen <t...@toke.dk>
> diff --git a/samples/bpf/xdp_sample_pkts_kern.c
> b/samples/bpf/xdp_sample_pkts_kern.c
> new file mode 100644
> index 000000000000..4560522ca015
> --- /dev/null
> +++ b/samples/bpf/xdp_sample_pkts_kern.c
> @@ -0,0 +1,62 @@
> +#include <linux/ptrace.h>
> +#include <linux/version.h>
> +#include <uapi/linux/bpf.h>
> +#include "bpf_helpers.h"
> +
> +#define SAMPLE_SIZE 64ul
> +#define MAX_CPUS 24
That may be a lil' too few for modern HW with hyper-threading on ;)
My development machine says:
$ ncpus
28
128, maybe?
> +#define bpf_printk(fmt, ...) \
> +({ \
> + char ____fmt[] = fmt; \
> + bpf_trace_printk(____fmt, sizeof(____fmt), \
> + ##__VA_ARGS__); \
> +})
> +
> +struct bpf_map_def SEC("maps") my_map = {
> + .type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
> + .key_size = sizeof(int),
> + .value_size = sizeof(u32),
> + .max_entries = MAX_CPUS,
> +};
> +
> +SEC("xdp_sample")
> +int xdp_sample_prog(struct xdp_md *ctx)
> +{
> + void *data_end = (void *)(long)ctx->data_end;
> + void *data = (void *)(long)ctx->data;
> +
> + /* Metadata will be in the perf event before the packet data. */
> + struct S {
> + u16 cookie;
> + u16 pkt_len;
> + } __attribute__((packed)) metadata;
> +
> + if (data + SAMPLE_SIZE < data_end) {
> + /* The XDP perf_event_output handler will use the upper 32 bits
> + * of the flags argument as a number of bytes to include of the
> + * packet payload in the event data. If the size is too big, the
> + * call to bpf_perf_event_output will fail and return -EFAULT.
> + *
> + * See bpf_xdp_event_output in net/core/filter.c.
> + *
> + * The BPF_F_CURRENT_CPU flag means that the event output fd
> + * will be indexed by the CPU number in the event map.
> + */
> + u64 flags = (SAMPLE_SIZE << 32) | BPF_F_CURRENT_CPU;
> + int ret;
> +
> + metadata.cookie = 0xdead;
> + metadata.pkt_len = (u16)(data_end - data);
> +
> + ret = bpf_perf_event_output(ctx, &my_map, flags,
> + &metadata, sizeof(metadata));
> + if(ret)
Please run checkpatch --strict on the samples.
> + bpf_printk("perf_event_output failed: %d\n", ret);
> + }
> +
> + return XDP_PASS;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> +u32 _version SEC("version") = LINUX_VERSION_CODE;
