BPF_MAP_TYPE_PERF_EVENT_ARRAY map is often used to send data from BPF program
to user space for additional processing. libbpf already has very low-level API
to read single CPU perf buffer, bpf_perf_event_read_simple(), but it's hard to
use and requires a lot of code to set everything up. This patch adds
perf_buffer abstraction on top of it, abstracting setting up and polling
per-CPU logic into simple and convenient API, similar to what BCC provides.
perf_buffer__new() sets up per-CPU ring buffers and updates corresponding BPF
map entries. It accepts two user-provided callbacks: one for handling raw
samples and one for get notifications of lost samples due to buffer overflow.
perf_buffer__poll() is used to fetch ring buffer data across all CPUs,
utilizing epoll instance.
perf_buffer__free() does corresponding clean up and unsets FDs from BPF map.
All APIs are not thread-safe. User should ensure proper locking/coordination if
used in multi-threaded set up.
Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
---
tools/lib/bpf/libbpf.c | 282 +++++++++++++++++++++++++++++++++++++++
tools/lib/bpf/libbpf.h | 12 ++
tools/lib/bpf/libbpf.map | 5 +-
3 files changed, 298 insertions(+), 1 deletion(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 9a4199b51300..c74cc535902a 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -32,7 +32,9 @@
#include <linux/limits.h>
#include <linux/perf_event.h>
#include <linux/ring_buffer.h>
+#include <sys/epoll.h>
#include <sys/ioctl.h>
+#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/vfs.h>
@@ -4322,6 +4324,286 @@ bpf_perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size,
return ret;
}
+struct perf_cpu_buf {
+ int fd;
+ void *base; /* mmap()'ed memory */
+ void *buf; /* for reconstructing segmented data */
+ size_t buf_size;
+};
+
+struct perf_buffer {
+ perf_buffer_sample_fn sample_cb;
+ perf_buffer_lost_fn lost_cb;
+ void *ctx; /* passed into callbacks */
+
+ size_t page_size;
+ size_t mmap_size;
+ struct perf_cpu_buf **cpu_bufs;
+ struct epoll_event *events;
+ int cpu_cnt;
+ int epfd; /* perf event FD */
+ int mapfd; /* BPF_MAP_TYPE_PERF_EVENT_ARRAY BPF map FD */
+};
+
+static void perf_buffer__free_cpu_buf(struct perf_buffer *pb,
+ struct perf_cpu_buf *cpu_buf, int cpu)
+{
+ if (!cpu_buf)
+ return;
+ if (cpu_buf->base &&
+ munmap(cpu_buf->base, pb->mmap_size + pb->page_size))
+ pr_warning("failed to munmap cpu_buf #%d\n", cpu);
+ if (cpu_buf->fd >= 0) {
+ ioctl(cpu_buf->fd, PERF_EVENT_IOC_DISABLE, 0);
+ close(cpu_buf->fd);
+ }
+ free(cpu_buf->buf);
+ free(cpu_buf);
+}
+
+void perf_buffer__free(struct perf_buffer *pb)
+{
+ int i;
+
+ if (!pb)
+ return;
+ if (pb->cpu_bufs) {
+ for (i = 0; i < pb->cpu_cnt && pb->cpu_bufs[i]; i++) {
+ struct perf_cpu_buf *cpu_buf = pb->cpu_bufs[i];
+
+ bpf_map_delete_elem(pb->mapfd, &i);
+ perf_buffer__free_cpu_buf(pb, cpu_buf, i);
+ }
+ free(pb->cpu_bufs);
+ }
+ if (pb->epfd >= 0)
+ close(pb->epfd);
+ free(pb->events);
+ free(pb);
+}
+
+static struct perf_cpu_buf *perf_buffer__open_cpu_buf(struct perf_buffer *pb,
+ int cpu)
+{
+ struct perf_event_attr attr = {};
+ struct perf_cpu_buf *cpu_buf;
+ char msg[STRERR_BUFSIZE];
+ int err;
+
+ cpu_buf = calloc(1, sizeof(*cpu_buf));
+ if (!cpu_buf)
+ return ERR_PTR(-ENOMEM);
+
+ attr.config = PERF_COUNT_SW_BPF_OUTPUT;
+ attr.type = PERF_TYPE_SOFTWARE;
+ attr.sample_type = PERF_SAMPLE_RAW;
+ attr.sample_period = 1;
+ attr.wakeup_events = 1;
+ cpu_buf->fd = syscall(__NR_perf_event_open, &attr, -1 /* pid */, cpu,
+ -1, PERF_FLAG_FD_CLOEXEC);
+ if (cpu_buf->fd < 0) {
+ err = -errno;
+ pr_warning("failed to open perf buffer event on cpu #%d: %s\n",
+ cpu, libbpf_strerror_r(err, msg, sizeof(msg)));
+ goto error;
+ }
+
+ cpu_buf->base = mmap(NULL, pb->mmap_size + pb->page_size,
+ PROT_READ | PROT_WRITE, MAP_SHARED,
+ cpu_buf->fd, 0);
+ if (cpu_buf->base == MAP_FAILED) {
+ cpu_buf->base = NULL;
+ err = -errno;
+ pr_warning("failed to mmap perf buffer on cpu #%d: %s\n",
+ cpu, libbpf_strerror_r(err, msg, sizeof(msg)));
+ goto error;
+ }
+
+ if (ioctl(cpu_buf->fd, PERF_EVENT_IOC_ENABLE, 0) < 0) {
+ err = -errno;
+ pr_warning("failed to enable perf buffer event on cpu #%d: %s\n",
+ cpu, libbpf_strerror_r(err, msg, sizeof(msg)));
+ goto error;
+ }
+
+ return cpu_buf;
+
+error:
+ perf_buffer__free_cpu_buf(pb, cpu_buf, cpu);
+ return (struct perf_cpu_buf *)ERR_PTR(err);
+}
+
+struct perf_buffer *perf_buffer__new(struct bpf_map *map, size_t page_cnt,
+ perf_buffer_sample_fn sample_cb,
+ perf_buffer_lost_fn lost_cb, void *ctx)
+{
+ char msg[STRERR_BUFSIZE];
+ struct perf_buffer *pb;
+ int err, cpu;
+
+ if (bpf_map__def(map)->type != BPF_MAP_TYPE_PERF_EVENT_ARRAY) {
+ pr_warning("map '%s' should be BPF_MAP_TYPE_PERF_EVENT_ARRAY\n",
+ bpf_map__name(map));
+ return ERR_PTR(-EINVAL);
+ }
+ if (bpf_map__fd(map) < 0) {
+ pr_warning("map '%s' doesn't have associated FD\n",
+ bpf_map__name(map));
+ return ERR_PTR(-EINVAL);
+ }
+ if (page_cnt & (page_cnt - 1)) {
+ pr_warning("page count should be power of two, but is %zu\n",
+ page_cnt);
+ return ERR_PTR(-EINVAL);
+ }
+
+ pb = calloc(1, sizeof(*pb));
+ if (!pb)
+ return ERR_PTR(-ENOMEM);
+
+ pb->sample_cb = sample_cb;
+ pb->lost_cb = lost_cb;
+ pb->ctx = ctx;
+ pb->page_size = getpagesize();
+ pb->mmap_size = pb->page_size * page_cnt;
+ pb->mapfd = bpf_map__fd(map);
+
+ pb->epfd = epoll_create1(EPOLL_CLOEXEC);
+ if (pb->epfd < 0) {
+ err = -errno;
+ pr_warning("failed to create epoll instance: %s\n",
+ libbpf_strerror_r(err, msg, sizeof(msg)));
+ goto error;
+ }
+
+ pb->cpu_cnt = libbpf_num_possible_cpus();
+ if (pb->cpu_cnt < 0) {
+ err = pb->cpu_cnt;
+ goto error;
+ }
+ pb->events = calloc(pb->cpu_cnt, sizeof(*pb->events));
+ if (!pb->events) {
+ err = -ENOMEM;
+ pr_warning("failed to allocate events: out of memory\n");
+ goto error;
+ }
+ pb->cpu_bufs = calloc(pb->cpu_cnt, sizeof(*pb->cpu_bufs));
+ if (!pb->cpu_bufs) {
+ err = -ENOMEM;
+ pr_warning("failed to allocate buffers: out of memory\n");
+ goto error;
+ }
+
+ for (cpu = 0; cpu < pb->cpu_cnt; cpu++) {
+ struct perf_cpu_buf *cpu_buf;
+
+ cpu_buf = perf_buffer__open_cpu_buf(pb, cpu);
+ if (IS_ERR(cpu_buf)) {
+ err = PTR_ERR(cpu_buf);
+ goto error;
+ }
+
+ pb->cpu_bufs[cpu] = cpu_buf;
+
+ err = bpf_map_update_elem(pb->mapfd, &cpu, &cpu_buf->fd, 0);
+ if (err) {
+ pr_warning("failed to set cpu #%d perf FD %d: %s\n",
+ cpu, cpu_buf->fd,
+ libbpf_strerror_r(err, msg, sizeof(msg)));
+ goto error;
+ }
+
+ pb->events[cpu].events = EPOLLIN;
+ pb->events[cpu].data.ptr = cpu_buf;
+ if (epoll_ctl(pb->epfd, EPOLL_CTL_ADD, cpu_buf->fd,
+ &pb->events[cpu]) < 0) {
+ err = -errno;
+ pr_warning("failed to epoll_ctl cpu #%d perf FD %d: %s\n",
+ cpu, cpu_buf->fd,
+ libbpf_strerror_r(err, msg, sizeof(msg)));
+ goto error;
+ }
+ }
+
+ return pb;
+
+error:
+ if (pb)
+ perf_buffer__free(pb);
+ return ERR_PTR(err);
+}
+
+struct perf_sample_raw {
+ struct perf_event_header header;
+ uint32_t size;
+ char data[0];
+};
+
+struct perf_sample_lost {
+ struct perf_event_header header;
+ uint64_t id;
+ uint64_t lost;
+ uint64_t sample_id;
+};
+
+static enum bpf_perf_event_ret
+perf_buffer__process_record(struct perf_event_header *e, void *ctx)
+{
+ struct perf_buffer *pb = ctx;
+ void *data = e;
+
+ switch (e->type) {
+ case PERF_RECORD_SAMPLE: {
+ struct perf_sample_raw *s = data;
+
+ pb->sample_cb(pb->ctx, s->data, s->size);
+ break;
+ }
+ case PERF_RECORD_LOST: {
+ struct perf_sample_lost *s = data;
+
+ if (pb->lost_cb)
+ pb->lost_cb(pb->ctx, s->lost);
+ break;
+ }
+ default:
+ pr_warning("unknown perf sample type %d\n", e->type);
+ return LIBBPF_PERF_EVENT_ERROR;
+ }
+ return LIBBPF_PERF_EVENT_CONT;
+}
+
+static int perf_buffer__process_records(struct perf_buffer *pb,
+ struct perf_cpu_buf *cpu_buf)
+{
+ enum bpf_perf_event_ret ret;
+
+ ret = bpf_perf_event_read_simple(cpu_buf->base, pb->mmap_size,
+ pb->page_size, &cpu_buf->buf,
+ &cpu_buf->buf_size,
+ perf_buffer__process_record, pb);
+ if (ret != LIBBPF_PERF_EVENT_CONT)
+ return ret;
+ return 0;
+}
+
+int perf_buffer__poll(struct perf_buffer *pb, int timeout_ms)
+{
+ int cnt, err;
+
+ cnt = epoll_wait(pb->epfd, pb->events, pb->cpu_cnt, timeout_ms);
+ for (int i = 0; i < cnt; i++) {
+ struct perf_cpu_buf *cpu_buf = pb->events[i].data.ptr;
+
+ err = perf_buffer__process_records(pb, cpu_buf);
+ if (err) {
+ pr_warning("error while processing records: %d\n", err);
+ return err;
+ }
+ }
+ return cnt < 0 ? -errno : cnt;
+}
+
struct bpf_prog_info_array_desc {
int array_offset; /* e.g. offset of jited_prog_insns */
int count_offset; /* e.g. offset of jited_prog_len */
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index bf7020a565c6..3bfde1a475ce 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -354,6 +354,18 @@ LIBBPF_API int bpf_prog_load(const char *file, enum bpf_prog_type type,
LIBBPF_API int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags);
LIBBPF_API int bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags);
+struct perf_buffer;
+typedef void (*perf_buffer_sample_fn)(void *ctx, void *data, __u32 size);
+typedef void (*perf_buffer_lost_fn)(void *ctx, __u64 cnt);
+
+LIBBPF_API struct perf_buffer *perf_buffer__new(struct bpf_map *map,
+ size_t page_cnt,
+ perf_buffer_sample_fn sample_cb,
+ perf_buffer_lost_fn lost_cb,
+ void *ctx);
+LIBBPF_API void perf_buffer__free(struct perf_buffer *pb);
+LIBBPF_API int perf_buffer__poll(struct perf_buffer *pb, int timeout_ms);
+
enum bpf_perf_event_ret {
LIBBPF_PERF_EVENT_DONE = 0,
LIBBPF_PERF_EVENT_ERROR = -1,
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 2382fbda4cbb..10f48103110a 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -170,13 +170,16 @@ LIBBPF_0.0.4 {
btf_dump__dump_type;
btf_dump__free;
btf_dump__new;
- btf__parse_elf;
bpf_object__load_xattr;
bpf_program__attach_kprobe;
bpf_program__attach_perf_event;
bpf_program__attach_raw_tracepoint;
bpf_program__attach_tracepoint;
bpf_program__attach_uprobe;
+ btf__parse_elf;
libbpf_num_possible_cpus;
libbpf_perf_event_disable_and_close;
+ perf_buffer__free;
+ perf_buffer__new;
+ perf_buffer__poll;
} LIBBPF_0.0.3;
--
2.17.1
