tools: bpftool: add simple perf event output reader

Users of BPF sooner or later discover perf_event_output() helpers
and BPF_MAP_TYPE_PERF_EVENT_ARRAY.  Dumping this array type is
not possible, however, we can add simple reading of perf events.
Create a new event_pipe subcommand for maps, this sub command
will only work with BPF_MAP_TYPE_PERF_EVENT_ARRAY maps.

Parts of the code from samples/bpf/trace_output_user.c.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/bpf/bpftool/map_perf_ring.c

@@ -0,0 +1,347 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (C) 2018 Netronome Systems, Inc. */
+/* This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+#include <errno.h>
+#include <fcntl.h>
+#include <libbpf.h>
+#include <poll.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include <unistd.h>
+#include <linux/bpf.h>
+#include <linux/perf_event.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sys/syscall.h>
+
+#include <bpf.h>
+#include <perf-sys.h>
+
+#include "main.h"
+
+#define MMAP_PAGE_CNT	16
+
+static bool stop;
+
+struct event_ring_info {
+	int fd;
+	int key;
+	unsigned int cpu;
+	void *mem;
+};
+
+struct perf_event_sample {
+	struct perf_event_header header;
+	__u32 size;
+	unsigned char data[];
+};
+
+static void int_exit(int signo)
+{
+	fprintf(stderr, "Stopping...\n");
+	stop = true;
+}
+
+static void
+print_bpf_output(struct event_ring_info *ring, struct perf_event_sample *e)
+{
+	struct {
+		struct perf_event_header header;
+		__u64 id;
+		__u64 lost;
+	} *lost = (void *)e;
+	struct timespec ts;
+
+	if (clock_gettime(CLOCK_MONOTONIC, &ts)) {
+		perror("Can't read clock for timestamp");
+		return;
+	}
+
+	if (json_output) {
+		jsonw_start_object(json_wtr);
+		jsonw_name(json_wtr, "timestamp");
+		jsonw_uint(json_wtr, ts.tv_sec * 1000000000ull + ts.tv_nsec);
+		jsonw_name(json_wtr, "type");
+		jsonw_uint(json_wtr, e->header.type);
+		jsonw_name(json_wtr, "cpu");
+		jsonw_uint(json_wtr, ring->cpu);
+		jsonw_name(json_wtr, "index");
+		jsonw_uint(json_wtr, ring->key);
+		if (e->header.type == PERF_RECORD_SAMPLE) {
+			jsonw_name(json_wtr, "data");
+			print_data_json(e->data, e->size);
+		} else if (e->header.type == PERF_RECORD_LOST) {
+			jsonw_name(json_wtr, "lost");
+			jsonw_start_object(json_wtr);
+			jsonw_name(json_wtr, "id");
+			jsonw_uint(json_wtr, lost->id);
+			jsonw_name(json_wtr, "count");
+			jsonw_uint(json_wtr, lost->lost);
+			jsonw_end_object(json_wtr);
+		}
+		jsonw_end_object(json_wtr);
+	} else {
+		if (e->header.type == PERF_RECORD_SAMPLE) {
+			printf("== @%ld.%ld CPU: %d index: %d =====\n",
+			       (long)ts.tv_sec, ts.tv_nsec,
+			       ring->cpu, ring->key);
+			fprint_hex(stdout, e->data, e->size, " ");
+			printf("\n");
+		} else if (e->header.type == PERF_RECORD_LOST) {
+			printf("lost %lld events\n", lost->lost);
+		} else {
+			printf("unknown event type=%d size=%d\n",
+			       e->header.type, e->header.size);
+		}
+	}
+}
+
+static void
+perf_event_read(struct event_ring_info *ring, void **buf, size_t *buf_len)
+{
+	volatile struct perf_event_mmap_page *header = ring->mem;
+	__u64 buffer_size = MMAP_PAGE_CNT * get_page_size();
+	__u64 data_tail = header->data_tail;
+	__u64 data_head = header->data_head;
+	void *base, *begin, *end;
+
+	asm volatile("" ::: "memory"); /* in real code it should be smp_rmb() */
+	if (data_head == data_tail)
+		return;
+
+	base = ((char *)header) + get_page_size();
+
+	begin = base + data_tail % buffer_size;
+	end = base + data_head % buffer_size;
+
+	while (begin != end) {
+		struct perf_event_sample *e;
+
+		e = begin;
+		if (begin + e->header.size > base + buffer_size) {
+			long len = base + buffer_size - begin;
+
+			if (*buf_len < e->header.size) {
+				free(*buf);
+				*buf = malloc(e->header.size);
+				if (!*buf) {
+					fprintf(stderr,
+						"can't allocate memory");
+					stop = true;
+					return;
+				}
+				*buf_len = e->header.size;
+			}
+
+			memcpy(*buf, begin, len);
+			memcpy(*buf + len, base, e->header.size - len);
+			e = (void *)*buf;
+			begin = base + e->header.size - len;
+		} else if (begin + e->header.size == base + buffer_size) {
+			begin = base;
+		} else {
+			begin += e->header.size;
+		}
+
+		print_bpf_output(ring, e);
+	}
+
+	__sync_synchronize(); /* smp_mb() */
+	header->data_tail = data_head;
+}
+
+static int perf_mmap_size(void)
+{
+	return get_page_size() * (MMAP_PAGE_CNT + 1);
+}
+
+static void *perf_event_mmap(int fd)
+{
+	int mmap_size = perf_mmap_size();
+	void *base;
+
+	base = mmap(NULL, mmap_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	if (base == MAP_FAILED) {
+		p_err("event mmap failed: %s\n", strerror(errno));
+		return NULL;
+	}
+
+	return base;
+}
+
+static void perf_event_unmap(void *mem)
+{
+	if (munmap(mem, perf_mmap_size()))
+		fprintf(stderr, "Can't unmap ring memory!\n");
+}
+
+static int bpf_perf_event_open(int map_fd, int key, int cpu)
+{
+	struct perf_event_attr attr = {
+		.sample_type = PERF_SAMPLE_RAW,
+		.type = PERF_TYPE_SOFTWARE,
+		.config = PERF_COUNT_SW_BPF_OUTPUT,
+	};
+	int pmu_fd;
+
+	pmu_fd = sys_perf_event_open(&attr, -1, cpu, -1, 0);
+	if (pmu_fd < 0) {
+		p_err("failed to open perf event %d for CPU %d", key, cpu);
+		return -1;
+	}
+
+	if (bpf_map_update_elem(map_fd, &key, &pmu_fd, BPF_ANY)) {
+		p_err("failed to update map for event %d for CPU %d", key, cpu);
+		goto err_close;
+	}
+	if (ioctl(pmu_fd, PERF_EVENT_IOC_ENABLE, 0)) {
+		p_err("failed to enable event %d for CPU %d", key, cpu);
+		goto err_close;
+	}
+
+	return pmu_fd;
+
+err_close:
+	close(pmu_fd);
+	return -1;
+}
+
+int do_event_pipe(int argc, char **argv)
+{
+	int i, nfds, map_fd, index = -1, cpu = -1;
+	struct bpf_map_info map_info = {};
+	struct event_ring_info *rings;
+	size_t tmp_buf_sz = 0;
+	void *tmp_buf = NULL;
+	struct pollfd *pfds;
+	__u32 map_info_len;
+	bool do_all = true;
+
+	map_info_len = sizeof(map_info);
+	map_fd = map_parse_fd_and_info(&argc, &argv, &map_info, &map_info_len);
+	if (map_fd < 0)
+		return -1;
+
+	if (map_info.type != BPF_MAP_TYPE_PERF_EVENT_ARRAY) {
+		p_err("map is not a perf event array");
+		goto err_close_map;
+	}
+
+	while (argc) {
+		if (argc < 2)
+			BAD_ARG();
+
+		if (is_prefix(*argv, "cpu")) {
+			char *endptr;
+
+			NEXT_ARG();
+			cpu = strtoul(*argv, &endptr, 0);
+			if (*endptr) {
+				p_err("can't parse %s as CPU ID", **argv);
+				goto err_close_map;
+			}
+
+			NEXT_ARG();
+		} else if (is_prefix(*argv, "index")) {
+			char *endptr;
+
+			NEXT_ARG();
+			index = strtoul(*argv, &endptr, 0);
+			if (*endptr) {
+				p_err("can't parse %s as index", **argv);
+				goto err_close_map;
+			}
+
+			NEXT_ARG();
+		} else {
+			BAD_ARG();
+		}
+
+		do_all = false;
+	}
+
+	if (!do_all) {
+		if (index == -1 || cpu == -1) {
+			p_err("cpu and index must be specified together");
+			goto err_close_map;
+		}
+
+		nfds = 1;
+	} else {
+		nfds = min(get_possible_cpus(), map_info.max_entries);
+		cpu = 0;
+		index = 0;
+	}
+
+	rings = calloc(nfds, sizeof(rings[0]));
+	if (!rings)
+		goto err_close_map;
+
+	pfds = calloc(nfds, sizeof(pfds[0]));
+	if (!pfds)
+		goto err_free_rings;
+
+	for (i = 0; i < nfds; i++) {
+		rings[i].cpu = cpu + i;
+		rings[i].key = index + i;
+
+		rings[i].fd = bpf_perf_event_open(map_fd, rings[i].key,
+						  rings[i].cpu);
+		if (rings[i].fd < 0)
+			goto err_close_fds_prev;
+
+		rings[i].mem = perf_event_mmap(rings[i].fd);
+		if (!rings[i].mem)
+			goto err_close_fds_current;
+
+		pfds[i].fd = rings[i].fd;
+		pfds[i].events = POLLIN;
+	}
+
+	signal(SIGINT, int_exit);
+	signal(SIGHUP, int_exit);
+	signal(SIGTERM, int_exit);
+
+	if (json_output)
+		jsonw_start_array(json_wtr);
+
+	while (!stop) {
+		poll(pfds, nfds, 200);
+		for (i = 0; i < nfds; i++)
+			perf_event_read(&rings[i], &tmp_buf, &tmp_buf_sz);
+	}
+	free(tmp_buf);
+
+	if (json_output)
+		jsonw_end_array(json_wtr);
+
+	for (i = 0; i < nfds; i++) {
+		perf_event_unmap(rings[i].mem);
+		close(rings[i].fd);
+	}
+	free(pfds);
+	free(rings);
+	close(map_fd);
+
+	return 0;
+
+err_close_fds_prev:
+	while (i--) {
+		perf_event_unmap(rings[i].mem);
+err_close_fds_current:
+		close(rings[i].fd);
+	}
+	free(pfds);
+err_free_rings:
+	free(rings);
+err_close_map:
+	close(map_fd);
+	return -1;
+}