Commit 3dca2115 authored by Daniel Borkmann's avatar Daniel Borkmann Committed by Alexei Starovoitov
Browse files

bpf, libbpf: simplify and cleanup perf ring buffer walk 



Simplify bpf_perf_event_read_simple() a bit and fix up some minor
things along the way: the return code in the header is not of type
int but enum bpf_perf_event_ret instead. Once callback indicated
to break the loop walking event data, it also needs to be consumed
in data_tail since it has been processed already.

Moreover, bpf_perf_event_print_t callback should avoid void * as
we actually get a pointer to struct perf_event_header and thus
applications can make use of container_of() to have type checks.
The walk also doesn't have to use modulo op since the ring size is
required to be power of two.

Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 84430d42

tools/bpf/bpftool/map_perf_ring.c

+6 −4
Original line number Diff line number Diff line
@@ -50,15 +50,17 @@ static void int_exit(int signo) 
	stop = true;

}



static enum bpf_perf_event_ret print_bpf_output(void *event, void *priv)

static enum bpf_perf_event_ret

print_bpf_output(struct perf_event_header *event, void *private_data)

{

	struct event_ring_info *ring = priv;

	struct perf_event_sample *e = event;

	struct perf_event_sample *e = container_of(event, struct perf_event_sample,

						   header);

	struct event_ring_info *ring = private_data;

	struct {

		struct perf_event_header header;

		__u64 id;

		__u64 lost;

	} *lost = event;

	} *lost = (typeof(lost))event;



	if (json_output) {

		jsonw_start_object(json_wtr);

tools/lib/bpf/libbpf.c

+29 −38
Original line number Diff line number Diff line
@@ -2415,56 +2415,47 @@ int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr, 
}



enum bpf_perf_event_ret

bpf_perf_event_read_simple(void *mem, unsigned long size,

			   unsigned long page_size, void **buf, size_t *buf_len,

			   bpf_perf_event_print_t fn, void *priv)

bpf_perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size,

			   void **copy_mem, size_t *copy_size,

			   bpf_perf_event_print_t fn, void *private_data)

{

	struct perf_event_mmap_page *header = mem;

	struct perf_event_mmap_page *header = mmap_mem;

	__u64 data_head = ring_buffer_read_head(header);

	__u64 data_tail = header->data_tail;

	int ret = LIBBPF_PERF_EVENT_ERROR;

	void *base, *begin, *end;



	if (data_head == data_tail)

		return LIBBPF_PERF_EVENT_CONT;



	base = ((char *)header) + page_size;



	begin = base + data_tail % size;

	end = base + data_head % size;



	while (begin != end) {

	void *base = ((__u8 *)header) + page_size;

	int ret = LIBBPF_PERF_EVENT_CONT;

	struct perf_event_header *ehdr;



		ehdr = begin;

		if (begin + ehdr->size > base + size) {

			long len = base + size - begin;



			if (*buf_len < ehdr->size) {

				free(*buf);

				*buf = malloc(ehdr->size);

				if (!*buf) {

	size_t ehdr_size;



	while (data_head != data_tail) {

		ehdr = base + (data_tail & (mmap_size - 1));

		ehdr_size = ehdr->size;



		if (((void *)ehdr) + ehdr_size > base + mmap_size) {

			void *copy_start = ehdr;

			size_t len_first = base + mmap_size - copy_start;

			size_t len_secnd = ehdr_size - len_first;



			if (*copy_size < ehdr_size) {

				free(*copy_mem);

				*copy_mem = malloc(ehdr_size);

				if (!*copy_mem) {

					*copy_size = 0;

					ret = LIBBPF_PERF_EVENT_ERROR;

					break;

				}

				*buf_len = ehdr->size;

				*copy_size = ehdr_size;

			}



			memcpy(*buf, begin, len);

			memcpy(*buf + len, base, ehdr->size - len);

			ehdr = (void *)*buf;

			begin = base + ehdr->size - len;

		} else if (begin + ehdr->size == base + size) {

			begin = base;

		} else {

			begin += ehdr->size;

			memcpy(*copy_mem, copy_start, len_first);

			memcpy(*copy_mem + len_first, base, len_secnd);

			ehdr = *copy_mem;

		}



		ret = fn(ehdr, priv);

		ret = fn(ehdr, private_data);

		data_tail += ehdr_size;

		if (ret != LIBBPF_PERF_EVENT_CONT)

			break;



		data_tail += ehdr->size;

	}



	ring_buffer_write_tail(header, data_tail);

tools/lib/bpf/libbpf.h

+8 −7
Original line number Diff line number Diff line
@@ -297,13 +297,14 @@ enum bpf_perf_event_ret { 
	LIBBPF_PERF_EVENT_CONT	= -2,

};



typedef enum bpf_perf_event_ret (*bpf_perf_event_print_t)(void *event,

							  void *priv);

LIBBPF_API int bpf_perf_event_read_simple(void *mem, unsigned long size,

					  unsigned long page_size,

					  void **buf, size_t *buf_len,

					  bpf_perf_event_print_t fn,

					  void *priv);

struct perf_event_header;

typedef enum bpf_perf_event_ret

	(*bpf_perf_event_print_t)(struct perf_event_header *hdr,

				  void *private_data);

LIBBPF_API enum bpf_perf_event_ret

bpf_perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size,

			   void **copy_mem, size_t *copy_size,

			   bpf_perf_event_print_t fn, void *private_data);



struct nlattr;

typedef int (*libbpf_dump_nlmsg_t)(void *cookie, void *msg, struct nlattr **tb);

tools/testing/selftests/bpf/trace_helpers.c

+4 −3
Original line number Diff line number Diff line
@@ -125,10 +125,11 @@ struct perf_event_sample { 
	char data[];

};



static enum bpf_perf_event_ret bpf_perf_event_print(void *event, void *priv)

static enum bpf_perf_event_ret

bpf_perf_event_print(struct perf_event_header *hdr, void *private_data)

{

	struct perf_event_sample *e = event;

	perf_event_print_fn fn = priv;

	struct perf_event_sample *e = (struct perf_event_sample *)hdr;

	perf_event_print_fn fn = private_data;

	int ret;



	if (e->header.type == PERF_RECORD_SAMPLE) {

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