Commit b3ce9079 authored by Andrii Nakryiko's avatar Andrii Nakryiko
Browse files

libbpf: Add per-program log buffer setter and getter 

Allow to set user-provided log buffer on a per-program basis ([0]). This
gives great deal of flexibility in terms of which programs are loaded
with logging enabled and where corresponding logs go.

Log buffer set with bpf_program__set_log_buf() overrides kernel_log_buf
and kernel_log_size settings set at bpf_object open time through
bpf_object_open_opts, if any.

Adjust bpf_object_load_prog_instance() logic to not perform own log buf
allocation and load retry if custom log buffer is provided by the user.

  [0] Closes: https://github.com/libbpf/libbpf/issues/418



Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211209193840.1248570-8-andrii@kernel.org
parent 2eda2145

tools/lib/bpf/libbpf.c

+75 −17
Original line number Diff line number Diff line
@@ -331,7 +331,11 @@ struct bpf_program { 


	struct reloc_desc *reloc_desc;

	int nr_reloc;

	int log_level;



	/* BPF verifier log settings */

	char *log_buf;

	size_t log_size;

	__u32 log_level;



	struct {

		int nr;
@@ -713,6 +717,9 @@ bpf_object__init_prog(struct bpf_object *obj, struct bpf_program *prog, 
	prog->instances.fds = NULL;

	prog->instances.nr = -1;



	/* inherit object's log_level */

	prog->log_level = obj->log_level;



	prog->sec_name = strdup(sec_name);

	if (!prog->sec_name)

		goto errout;
@@ -6591,8 +6598,10 @@ static int bpf_object_load_prog_instance(struct bpf_object *obj, struct bpf_prog 
	const char *prog_name = NULL;

	char *cp, errmsg[STRERR_BUFSIZE];

	size_t log_buf_size = 0;

	char *log_buf = NULL;

	char *log_buf = NULL, *tmp;

	int btf_fd, ret, err;

	bool own_log_buf = true;

	__u32 log_level = prog->log_level;



	if (prog->type == BPF_PROG_TYPE_UNSPEC) {

		/*
@@ -6627,7 +6636,7 @@ static int bpf_object_load_prog_instance(struct bpf_object *obj, struct bpf_prog 
		load_attr.line_info_rec_size = prog->line_info_rec_size;

		load_attr.line_info_cnt = prog->line_info_cnt;

	}

	load_attr.log_level = prog->log_level;

	load_attr.log_level = log_level;

	load_attr.prog_flags = prog->prog_flags;

	load_attr.fd_array = obj->fd_array;
@@ -6648,21 +6657,42 @@ static int bpf_object_load_prog_instance(struct bpf_object *obj, struct bpf_prog 
		*prog_fd = -1;

		return 0;

	}

retry_load:

	if (log_buf_size) {

		log_buf = malloc(log_buf_size);

		if (!log_buf)

			return -ENOMEM;



		*log_buf = 0;

retry_load:

	/* if log_level is zero, we don't request logs initiallly even if

	 * custom log_buf is specified; if the program load fails, then we'll

	 * bump log_level to 1 and use either custom log_buf or we'll allocate

	 * our own and retry the load to get details on what failed

	 */

	if (log_level) {

		if (prog->log_buf) {

			log_buf = prog->log_buf;

			log_buf_size = prog->log_size;

			own_log_buf = false;

		} else if (obj->log_buf) {

			log_buf = obj->log_buf;

			log_buf_size = obj->log_size;

			own_log_buf = false;

		} else {

			log_buf_size = max((size_t)BPF_LOG_BUF_SIZE, log_buf_size * 2);

			tmp = realloc(log_buf, log_buf_size);

			if (!tmp) {

				ret = -ENOMEM;

				goto out;

			}

			log_buf = tmp;

			log_buf[0] = '\0';

			own_log_buf = true;

		}

	}



	load_attr.log_buf = log_buf;

	load_attr.log_size = log_buf_size;

	ret = bpf_prog_load(prog->type, prog_name, license, insns, insns_cnt, &load_attr);

	load_attr.log_level = log_level;



	ret = bpf_prog_load(prog->type, prog_name, license, insns, insns_cnt, &load_attr);

	if (ret >= 0) {

		if (log_buf && load_attr.log_level) {

		if (log_level && own_log_buf) {

			pr_debug("prog '%s': -- BEGIN PROG LOAD LOG --\n%s-- END PROG LOAD LOG --\n",

				 prog->name, log_buf);

		}
@@ -6690,19 +6720,26 @@ static int bpf_object_load_prog_instance(struct bpf_object *obj, struct bpf_prog 
		goto out;

	}



	if (!log_buf || errno == ENOSPC) {

		log_buf_size = max((size_t)BPF_LOG_BUF_SIZE,

				   log_buf_size << 1);

		free(log_buf);

	if (log_level == 0) {

		log_level = 1;

		goto retry_load;

	}

	/* On ENOSPC, increase log buffer size and retry, unless custom

	 * log_buf is specified.

	 * Be careful to not overflow u32, though. Kernel's log buf size limit

	 * isn't part of UAPI so it can always be bumped to full 4GB. So don't

	 * multiply by 2 unless we are sure we'll fit within 32 bits.

	 * Currently, we'll get -EINVAL when we reach (UINT_MAX >> 2).

	 */

	if (own_log_buf && errno == ENOSPC && log_buf_size <= UINT_MAX / 2)

		goto retry_load;



	ret = -errno;

	cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));

	pr_warn("prog '%s': BPF program load failed: %s\n", prog->name, cp);

	pr_perm_msg(ret);



	if (log_buf && log_buf[0] != '\0') {

	if (own_log_buf && log_buf && log_buf[0] != '\0') {

		pr_warn("prog '%s': -- BEGIN PROG LOAD LOG --\n%s-- END PROG LOAD LOG --\n",

			prog->name, log_buf);

	}
@@ -6712,6 +6749,7 @@ static int bpf_object_load_prog_instance(struct bpf_object *obj, struct bpf_prog 
	}



out:

	if (own_log_buf)

		free(log_buf);

	return ret;

}
@@ -8498,6 +8536,26 @@ int bpf_program__set_log_level(struct bpf_program *prog, __u32 log_level) 
	return 0;

}



const char *bpf_program__log_buf(const struct bpf_program *prog, size_t *log_size)

{

	*log_size = prog->log_size;

	return prog->log_buf;

}



int bpf_program__set_log_buf(struct bpf_program *prog, char *log_buf, size_t log_size)

{

	if (log_size && !log_buf)

		return -EINVAL;

	if (prog->log_size > UINT_MAX)

		return -EINVAL;

	if (prog->obj->loaded)

		return -EBUSY;



	prog->log_buf = log_buf;

	prog->log_size = log_size;

	return 0;

}



#define SEC_DEF(sec_pfx, ptype, atype, flags, ...) {			    \

	.sec = sec_pfx,							    \

	.prog_type = BPF_PROG_TYPE_##ptype,				    \

tools/lib/bpf/libbpf.h

+7 −0
Original line number Diff line number Diff line
@@ -591,8 +591,15 @@ bpf_program__set_expected_attach_type(struct bpf_program *prog, 


LIBBPF_API __u32 bpf_program__flags(const struct bpf_program *prog);

LIBBPF_API int bpf_program__set_flags(struct bpf_program *prog, __u32 flags);



/* Per-program log level and log buffer getters/setters.

 * See bpf_object_open_opts comments regarding log_level and log_buf

 * interactions.

 */

LIBBPF_API __u32 bpf_program__log_level(const struct bpf_program *prog);

LIBBPF_API int bpf_program__set_log_level(struct bpf_program *prog, __u32 log_level);

LIBBPF_API const char *bpf_program__log_buf(const struct bpf_program *prog, size_t *log_size);

LIBBPF_API int bpf_program__set_log_buf(struct bpf_program *prog, char *log_buf, size_t log_size);



LIBBPF_API int

bpf_program__set_attach_target(struct bpf_program *prog, int attach_prog_fd,

tools/lib/bpf/libbpf.map

+2 −0
Original line number Diff line number Diff line
@@ -423,6 +423,8 @@ LIBBPF_0.6.0 { 
LIBBPF_0.7.0 {

	global:

		bpf_btf_load;

		bpf_program__log_buf;

		bpf_program__log_level;

		bpf_program__set_log_buf;

		bpf_program__set_log_level;

};