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Commit fb84b822 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Daniel Borkmann
Browse files

libbpf: add perf buffer API 



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__new_raw() is similar, but provides more control over how
perf events are set up (by accepting user-provided perf_event_attr), how
they are handled (perf_event_header pointer is passed directly to
user-provided callback), and on which CPUs ring buffers are created
(it's possible to provide a list of CPUs and corresponding map keys to
update). This API allows advanced users fuller control.

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: default avatarAndrii Nakryiko <andriin@fb.com>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent c3ec002e

tools/lib/bpf/libbpf.c

+366 −0
Original line number Diff line number Diff line
@@ -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>
@@ -4354,6 +4356,370 @@ bpf_perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size, 
	return ret;

}



struct perf_buffer;



struct perf_buffer_params {

	struct perf_event_attr *attr;

	/* if event_cb is specified, it takes precendence */

	perf_buffer_event_fn event_cb;

	/* sample_cb and lost_cb are higher-level common-case callbacks */

	perf_buffer_sample_fn sample_cb;

	perf_buffer_lost_fn lost_cb;

	void *ctx;

	int cpu_cnt;

	int *cpus;

	int *map_keys;

};



struct perf_cpu_buf {

	struct perf_buffer *pb;

	void *base; /* mmap()'ed memory */

	void *buf; /* for reconstructing segmented data */

	size_t buf_size;

	int fd;

	int cpu;

	int map_key;

};



struct perf_buffer {

	perf_buffer_event_fn event_cb;

	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 epoll_fd; /* perf event FD */

	int map_fd; /* 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)

{

	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_buf->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->map_fd, &cpu_buf->map_key);

			perf_buffer__free_cpu_buf(pb, cpu_buf);

		}

		free(pb->cpu_bufs);

	}

	if (pb->epoll_fd >= 0)

		close(pb->epoll_fd);

	free(pb->events);

	free(pb);

}



static struct perf_cpu_buf *

perf_buffer__open_cpu_buf(struct perf_buffer *pb, struct perf_event_attr *attr,

			  int cpu, int map_key)

{

	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);



	cpu_buf->pb = pb;

	cpu_buf->cpu = cpu;

	cpu_buf->map_key = map_key;



	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);

	return (struct perf_cpu_buf *)ERR_PTR(err);

}



static struct perf_buffer *__perf_buffer__new(int map_fd, size_t page_cnt,

					      struct perf_buffer_params *p);



struct perf_buffer *perf_buffer__new(int map_fd, size_t page_cnt,

				     const struct perf_buffer_opts *opts)

{

	struct perf_buffer_params p = {};

	struct perf_event_attr attr = {

		.config = PERF_COUNT_SW_BPF_OUTPUT,

		.type = PERF_TYPE_SOFTWARE,

		.sample_type = PERF_SAMPLE_RAW,

		.sample_period = 1,

		.wakeup_events = 1,

	};



	p.attr = &attr;

	p.sample_cb = opts ? opts->sample_cb : NULL;

	p.lost_cb = opts ? opts->lost_cb : NULL;

	p.ctx = opts ? opts->ctx : NULL;



	return __perf_buffer__new(map_fd, page_cnt, &p);

}



struct perf_buffer *

perf_buffer__new_raw(int map_fd, size_t page_cnt,

		     const struct perf_buffer_raw_opts *opts)

{

	struct perf_buffer_params p = {};



	p.attr = opts->attr;

	p.event_cb = opts->event_cb;

	p.ctx = opts->ctx;

	p.cpu_cnt = opts->cpu_cnt;

	p.cpus = opts->cpus;

	p.map_keys = opts->map_keys;



	return __perf_buffer__new(map_fd, page_cnt, &p);

}



static struct perf_buffer *__perf_buffer__new(int map_fd, size_t page_cnt,

					      struct perf_buffer_params *p)

{

	struct bpf_map_info map = {};

	char msg[STRERR_BUFSIZE];

	struct perf_buffer *pb;

	__u32 map_info_len;

	int err, i;



	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);

	}



	map_info_len = sizeof(map);

	err = bpf_obj_get_info_by_fd(map_fd, &map, &map_info_len);

	if (err) {

		err = -errno;

		pr_warning("failed to get map info for map FD %d: %s\n",

			   map_fd, libbpf_strerror_r(err, msg, sizeof(msg)));

		return ERR_PTR(err);

	}



	if (map.type != BPF_MAP_TYPE_PERF_EVENT_ARRAY) {

		pr_warning("map '%s' should be BPF_MAP_TYPE_PERF_EVENT_ARRAY\n",

			   map.name);

		return ERR_PTR(-EINVAL);

	}



	pb = calloc(1, sizeof(*pb));

	if (!pb)

		return ERR_PTR(-ENOMEM);



	pb->event_cb = p->event_cb;

	pb->sample_cb = p->sample_cb;

	pb->lost_cb = p->lost_cb;

	pb->ctx = p->ctx;



	pb->page_size = getpagesize();

	pb->mmap_size = pb->page_size * page_cnt;

	pb->map_fd = map_fd;



	pb->epoll_fd = epoll_create1(EPOLL_CLOEXEC);

	if (pb->epoll_fd < 0) {

		err = -errno;

		pr_warning("failed to create epoll instance: %s\n",

			   libbpf_strerror_r(err, msg, sizeof(msg)));

		goto error;

	}



	if (p->cpu_cnt > 0) {

		pb->cpu_cnt = p->cpu_cnt;

	} else {

		pb->cpu_cnt = libbpf_num_possible_cpus();

		if (pb->cpu_cnt < 0) {

			err = pb->cpu_cnt;

			goto error;

		}

		if (map.max_entries < pb->cpu_cnt)

			pb->cpu_cnt = map.max_entries;

	}



	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 (i = 0; i < pb->cpu_cnt; i++) {

		struct perf_cpu_buf *cpu_buf;

		int cpu, map_key;



		cpu = p->cpu_cnt > 0 ? p->cpus[i] : i;

		map_key = p->cpu_cnt > 0 ? p->map_keys[i] : i;



		cpu_buf = perf_buffer__open_cpu_buf(pb, p->attr, cpu, map_key);

		if (IS_ERR(cpu_buf)) {

			err = PTR_ERR(cpu_buf);

			goto error;

		}



		pb->cpu_bufs[i] = cpu_buf;



		err = bpf_map_update_elem(pb->map_fd, &map_key,

					  &cpu_buf->fd, 0);

		if (err) {

			err = -errno;

			pr_warning("failed to set cpu #%d, key %d -> perf FD %d: %s\n",

				   cpu, map_key, cpu_buf->fd,

				   libbpf_strerror_r(err, msg, sizeof(msg)));

			goto error;

		}



		pb->events[i].events = EPOLLIN;

		pb->events[i].data.ptr = cpu_buf;

		if (epoll_ctl(pb->epoll_fd, EPOLL_CTL_ADD, cpu_buf->fd,

			      &pb->events[i]) < 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_cpu_buf *cpu_buf = ctx;

	struct perf_buffer *pb = cpu_buf->pb;

	void *data = e;



	/* user wants full control over parsing perf event */

	if (pb->event_cb)

		return pb->event_cb(pb->ctx, cpu_buf->cpu, e);



	switch (e->type) {

	case PERF_RECORD_SAMPLE: {

		struct perf_sample_raw *s = data;



		if (pb->sample_cb)

			pb->sample_cb(pb->ctx, cpu_buf->cpu, s->data, s->size);

		break;

	}

	case PERF_RECORD_LOST: {

		struct perf_sample_lost *s = data;



		if (pb->lost_cb)

			pb->lost_cb(pb->ctx, cpu_buf->cpu, 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, cpu_buf);

	if (ret != LIBBPF_PERF_EVENT_CONT)

		return ret;

	return 0;

}



int perf_buffer__poll(struct perf_buffer *pb, int timeout_ms)

{

	int i, cnt, err;



	cnt = epoll_wait(pb->epoll_fd, pb->events, pb->cpu_cnt, timeout_ms);

	for (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 */

tools/lib/bpf/libbpf.h

+49 −0
Original line number Diff line number Diff line
@@ -358,6 +358,26 @@ 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, int cpu,

				      void *data, __u32 size);

typedef void (*perf_buffer_lost_fn)(void *ctx, int cpu, __u64 cnt);



/* common use perf buffer options */

struct perf_buffer_opts {

	/* if specified, sample_cb is called for each sample */

	perf_buffer_sample_fn sample_cb;

	/* if specified, lost_cb is called for each batch of lost samples */

	perf_buffer_lost_fn lost_cb;

	/* ctx is provided to sample_cb and lost_cb */

	void *ctx;

};



LIBBPF_API struct perf_buffer *

perf_buffer__new(int map_fd, size_t page_cnt,

		 const struct perf_buffer_opts *opts);



enum bpf_perf_event_ret {

	LIBBPF_PERF_EVENT_DONE	= 0,

	LIBBPF_PERF_EVENT_ERROR	= -1,
@@ -365,6 +385,35 @@ enum bpf_perf_event_ret { 
};



struct perf_event_header;



typedef enum bpf_perf_event_ret

(*perf_buffer_event_fn)(void *ctx, int cpu, struct perf_event_header *event);



/* raw perf buffer options, giving most power and control */

struct perf_buffer_raw_opts {

	/* perf event attrs passed directly into perf_event_open() */

	struct perf_event_attr *attr;

	/* raw event callback */

	perf_buffer_event_fn event_cb;

	/* ctx is provided to event_cb */

	void *ctx;

	/* if cpu_cnt == 0, open all on all possible CPUs (up to the number of

	 * max_entries of given PERF_EVENT_ARRAY map)

	 */

	int cpu_cnt;

	/* if cpu_cnt > 0, cpus is an array of CPUs to open ring buffers on */

	int *cpus;

	/* if cpu_cnt > 0, map_keys specify map keys to set per-CPU FDs for */

	int *map_keys;

};



LIBBPF_API struct perf_buffer *

perf_buffer__new_raw(int map_fd, size_t page_cnt,

		     const struct perf_buffer_raw_opts *opts);



LIBBPF_API void perf_buffer__free(struct perf_buffer *pb);

LIBBPF_API int perf_buffer__poll(struct perf_buffer *pb, int timeout_ms);



typedef enum bpf_perf_event_ret

	(*bpf_perf_event_print_t)(struct perf_event_header *hdr,

				  void *private_data);

tools/lib/bpf/libbpf.map

+4 −0
Original line number Diff line number Diff line
@@ -179,4 +179,8 @@ LIBBPF_0.0.4 { 
		btf_dump__new;

		btf__parse_elf;

		libbpf_num_possible_cpus;

		perf_buffer__free;

		perf_buffer__new;

		perf_buffer__new_raw;

		perf_buffer__poll;

} LIBBPF_0.0.3;