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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: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211209193840.1248570-8-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2021-12-09 11:38:35 -08:00
parent 2eda2145eb
commit b3ce907950
3 changed files with 84 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

92
tools/lib/bpf/libbpf.c
View File

@ -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 @@ retry_load:
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);
}
@ -6712,7 +6749,8 @@ retry_load:
}
out:
free(log_buf);
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, \

7
tools/lib/bpf/libbpf.h
View File

@ -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,

2
tools/lib/bpf/libbpf.map
View File

@ -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;
};