samples/bpf: Add xdp_sample_pkts example

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.

Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 169 insertions, 0 deletions

diff --git a/samples/bpf/xdp_sample_pkts_user.c b/samples/bpf/xdp_sample_pkts_user.c
new file mode 100644
index 000000000000..8dd87c1eb560
--- /dev/null
+++ b/samples/bpf/xdp_sample_pkts_user.c
@@ -0,0 +1,169 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <linux/perf_event.h>
+#include <linux/bpf.h>
+#include <net/if.h>
+#include <errno.h>
+#include <assert.h>
+#include <sys/sysinfo.h>
+#include <sys/ioctl.h>
+#include <signal.h>
+#include <libbpf.h>
+#include <bpf/bpf.h>
+
+#include "perf-sys.h"
+#include "trace_helpers.h"
+
+#define MAX_CPUS 128
+static int pmu_fds[MAX_CPUS], if_idx;
+static struct perf_event_mmap_page *headers[MAX_CPUS];
+static char *if_name;
+
+static int do_attach(int idx, int fd, const char *name)
+{
+	int err;
+
+	err = bpf_set_link_xdp_fd(idx, fd, 0);
+	if (err < 0)
+		printf("ERROR: failed to attach program to %s\n", name);
+
+	return err;
+}
+
+static int do_detach(int idx, const char *name)
+{
+	int err;
+
+	err = bpf_set_link_xdp_fd(idx, -1, 0);
+	if (err < 0)
+		printf("ERROR: failed to detach program from %s\n", name);
+
+	return err;
+}
+
+#define SAMPLE_SIZE 64
+
+static int print_bpf_output(void *data, int size)
+{
+	struct {
+		__u16 cookie;
+		__u16 pkt_len;
+		__u8  pkt_data[SAMPLE_SIZE];
+	} __packed *e = data;
+	int i;
+
+	if (e->cookie != 0xdead) {
+		printf("BUG cookie %x sized %d\n",
+		       e->cookie, size);
+		return LIBBPF_PERF_EVENT_ERROR;
+	}
+
+	printf("Pkt len: %-5d bytes. Ethernet hdr: ", e->pkt_len);
+	for (i = 0; i < 14 && i < e->pkt_len; i++)
+		printf("%02x ", e->pkt_data[i]);
+	printf("\n");
+
+	return LIBBPF_PERF_EVENT_CONT;
+}
+
+static void test_bpf_perf_event(int map_fd, int num)
+{
+	struct perf_event_attr attr = {
+		.sample_type = PERF_SAMPLE_RAW,
+		.type = PERF_TYPE_SOFTWARE,
+		.config = PERF_COUNT_SW_BPF_OUTPUT,
+		.wakeup_events = 1, /* get an fd notification for every event */
+	};
+	int i;
+
+	for (i = 0; i < num; i++) {
+		int key = i;
+
+		pmu_fds[i] = sys_perf_event_open(&attr, -1/*pid*/, i/*cpu*/,
+						 -1/*group_fd*/, 0);
+
+		assert(pmu_fds[i] >= 0);
+		assert(bpf_map_update_elem(map_fd, &key,
+					   &pmu_fds[i], BPF_ANY) == 0);
+		ioctl(pmu_fds[i], PERF_EVENT_IOC_ENABLE, 0);
+	}
+}
+
+static void sig_handler(int signo)
+{
+	do_detach(if_idx, if_name);
+	exit(0);
+}
+
+int main(int argc, char **argv)
+{
+	struct bpf_prog_load_attr prog_load_attr = {
+		.prog_type	= BPF_PROG_TYPE_XDP,
+	};
+	struct bpf_object *obj;
+	struct bpf_map *map;
+	int prog_fd, map_fd;
+	char filename[256];
+	int ret, err, i;
+	int numcpus;
+
+	if (argc < 2) {
+		printf("Usage: %s <ifname>\n", argv[0]);
+		return 1;
+	}
+
+	numcpus = get_nprocs();
+	if (numcpus > MAX_CPUS)
+		numcpus = MAX_CPUS;
+
+	snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
+	prog_load_attr.file = filename;
+
+	if (bpf_prog_load_xattr(&prog_load_attr, &obj, &prog_fd))
+		return 1;
+
+	if (!prog_fd) {
+		printf("load_bpf_file: %s\n", strerror(errno));
+		return 1;
+	}
+
+	map = bpf_map__next(NULL, obj);
+	if (!map) {
+		printf("finding a map in obj file failed\n");
+		return 1;
+	}
+	map_fd = bpf_map__fd(map);
+
+	if_idx = if_nametoindex(argv[1]);
+	if (!if_idx)
+		if_idx = strtoul(argv[1], NULL, 0);
+
+	if (!if_idx) {
+		fprintf(stderr, "Invalid ifname\n");
+		return 1;
+	}
+	if_name = argv[1];
+	err = do_attach(if_idx, prog_fd, argv[1]);
+	if (err)
+		return err;
+
+	if (signal(SIGINT, sig_handler) ||
+	    signal(SIGHUP, sig_handler) ||
+	    signal(SIGTERM, sig_handler)) {
+		perror("signal");
+		return 1;
+	}
+
+	test_bpf_perf_event(map_fd, numcpus);
+
+	for (i = 0; i < numcpus; i++)
+		if (perf_event_mmap_header(pmu_fds[i], &headers[i]) < 0)
+			return 1;
+
+	ret = perf_event_poller_multi(pmu_fds, headers, numcpus,
+				      print_bpf_output);
+	kill(0, SIGINT);
+	return ret;
+}