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libbpf: Allow to augment system Kconfig through extra optional config
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Instead of all or nothing approach of overriding Kconfig file location, allow
to extend it with extra values and override chosen subset of values though
optional user-provided extra config, passed as a string through open options'
.kconfig option. If same config key is present in both user-supplied config
and Kconfig, user-supplied one wins. This allows applications to more easily
test various conditions despite host kernel's real configuration. If all of
BPF object's __kconfig externs are satisfied from user-supplied config, system
Kconfig won't be read at all.

Simplify selftests by not needing to create temporary Kconfig files.

Suggested-by: Alexei Starovoitov <ast@fb.com>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191219002837.3074619-3-andriin@fb.com
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Andrii Nakryiko authored and Alexei Starovoitov committed Dec 19, 2019
1 parent 81bfdd0 commit 8601fd4
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Showing 3 changed files with 132 additions and 112 deletions.
204 changes: 124 additions & 80 deletions tools/lib/bpf/libbpf.c
Original file line number Diff line number Diff line change
Expand Up @@ -302,7 +302,7 @@ struct bpf_object {
size_t nr_maps;
size_t maps_cap;

char *kconfig_path;
char *kconfig;
struct extern_desc *externs;
int nr_extern;
int kconfig_map_idx;
Expand Down Expand Up @@ -1149,98 +1149,129 @@ static int set_ext_value_num(struct extern_desc *ext, void *ext_val,
return 0;
}

static int bpf_object__read_kernel_config(struct bpf_object *obj,
const char *config_path,
void *data)
static int bpf_object__process_kconfig_line(struct bpf_object *obj,
char *buf, void *data)
{
char buf[PATH_MAX], *sep, *value;
struct extern_desc *ext;
char *sep, *value;
int len, err = 0;
void *ext_val;
__u64 num;
gzFile file;

if (config_path) {
file = gzopen(config_path, "r");
} else {
struct utsname uts;
if (strncmp(buf, "CONFIG_", 7))
return 0;

uname(&uts);
len = snprintf(buf, PATH_MAX, "/boot/config-%s", uts.release);
if (len < 0)
return -EINVAL;
else if (len >= PATH_MAX)
return -ENAMETOOLONG;
/* gzopen also accepts uncompressed files. */
file = gzopen(buf, "r");
if (!file)
file = gzopen("/proc/config.gz", "r");
sep = strchr(buf, '=');
if (!sep) {
pr_warn("failed to parse '%s': no separator\n", buf);
return -EINVAL;
}

/* Trim ending '\n' */
len = strlen(buf);
if (buf[len - 1] == '\n')
buf[len - 1] = '\0';
/* Split on '=' and ensure that a value is present. */
*sep = '\0';
if (!sep[1]) {
*sep = '=';
pr_warn("failed to parse '%s': no value\n", buf);
return -EINVAL;
}

ext = find_extern_by_name(obj, buf);
if (!ext || ext->is_set)
return 0;

ext_val = data + ext->data_off;
value = sep + 1;

switch (*value) {
case 'y': case 'n': case 'm':
err = set_ext_value_tri(ext, ext_val, *value);
break;
case '"':
err = set_ext_value_str(ext, ext_val, value);
break;
default:
/* assume integer */
err = parse_u64(value, &num);
if (err) {
pr_warn("extern %s=%s should be integer\n",
ext->name, value);
return err;
}
err = set_ext_value_num(ext, ext_val, num);
break;
}
if (err)
return err;
pr_debug("extern %s=%s\n", ext->name, value);
return 0;
}

static int bpf_object__read_kconfig_file(struct bpf_object *obj, void *data)
{
char buf[PATH_MAX];
struct utsname uts;
int len, err = 0;
gzFile file;

uname(&uts);
len = snprintf(buf, PATH_MAX, "/boot/config-%s", uts.release);
if (len < 0)
return -EINVAL;
else if (len >= PATH_MAX)
return -ENAMETOOLONG;

/* gzopen also accepts uncompressed files. */
file = gzopen(buf, "r");
if (!file)
file = gzopen("/proc/config.gz", "r");

if (!file) {
pr_warn("failed to read kernel config at '%s'\n", config_path);
pr_warn("failed to open system Kconfig\n");
return -ENOENT;
}

while (gzgets(file, buf, sizeof(buf))) {
if (strncmp(buf, "CONFIG_", 7))
continue;

sep = strchr(buf, '=');
if (!sep) {
err = -EINVAL;
pr_warn("failed to parse '%s': no separator\n", buf);
goto out;
}
/* Trim ending '\n' */
len = strlen(buf);
if (buf[len - 1] == '\n')
buf[len - 1] = '\0';
/* Split on '=' and ensure that a value is present. */
*sep = '\0';
if (!sep[1]) {
err = -EINVAL;
*sep = '=';
pr_warn("failed to parse '%s': no value\n", buf);
err = bpf_object__process_kconfig_line(obj, buf, data);
if (err) {
pr_warn("error parsing system Kconfig line '%s': %d\n",
buf, err);
goto out;
}
}

ext = find_extern_by_name(obj, buf);
if (!ext)
continue;
if (ext->is_set) {
err = -EINVAL;
pr_warn("re-defining extern '%s' not allowed\n", buf);
goto out;
}
out:
gzclose(file);
return err;
}

ext_val = data + ext->data_off;
value = sep + 1;
static int bpf_object__read_kconfig_mem(struct bpf_object *obj,
const char *config, void *data)
{
char buf[PATH_MAX];
int err = 0;
FILE *file;

switch (*value) {
case 'y': case 'n': case 'm':
err = set_ext_value_tri(ext, ext_val, *value);
break;
case '"':
err = set_ext_value_str(ext, ext_val, value);
break;
default:
/* assume integer */
err = parse_u64(value, &num);
if (err) {
pr_warn("extern %s=%s should be integer\n",
ext->name, value);
goto out;
}
err = set_ext_value_num(ext, ext_val, num);
file = fmemopen((void *)config, strlen(config), "r");
if (!file) {
err = -errno;
pr_warn("failed to open in-memory Kconfig: %d\n", err);
return err;
}

while (fgets(buf, sizeof(buf), file)) {
err = bpf_object__process_kconfig_line(obj, buf, data);
if (err) {
pr_warn("error parsing in-memory Kconfig line '%s': %d\n",
buf, err);
break;
}
if (err)
goto out;
pr_debug("extern %s=%s\n", ext->name, value);
}

out:
gzclose(file);
fclose(file);
return err;
}

Expand Down Expand Up @@ -4567,7 +4598,7 @@ static struct bpf_object *
__bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
const struct bpf_object_open_opts *opts)
{
const char *obj_name, *kconfig_path;
const char *obj_name, *kconfig;
struct bpf_program *prog;
struct bpf_object *obj;
char tmp_name[64];
Expand Down Expand Up @@ -4599,10 +4630,10 @@ __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
return obj;

obj->relaxed_core_relocs = OPTS_GET(opts, relaxed_core_relocs, false);
kconfig_path = OPTS_GET(opts, kconfig_path, NULL);
if (kconfig_path) {
obj->kconfig_path = strdup(kconfig_path);
if (!obj->kconfig_path)
kconfig = OPTS_GET(opts, kconfig, NULL);
if (kconfig) {
obj->kconfig = strdup(kconfig);
if (!obj->kconfig)
return ERR_PTR(-ENOMEM);
}

Expand Down Expand Up @@ -4745,7 +4776,7 @@ static int bpf_object__sanitize_maps(struct bpf_object *obj)
}

static int bpf_object__resolve_externs(struct bpf_object *obj,
const char *config_path)
const char *extra_kconfig)
{
bool need_config = false;
struct extern_desc *ext;
Expand Down Expand Up @@ -4779,8 +4810,21 @@ static int bpf_object__resolve_externs(struct bpf_object *obj,
return -EINVAL;
}
}
if (need_config && extra_kconfig) {
err = bpf_object__read_kconfig_mem(obj, extra_kconfig, data);
if (err)
return -EINVAL;
need_config = false;
for (i = 0; i < obj->nr_extern; i++) {
ext = &obj->externs[i];
if (!ext->is_set) {
need_config = true;
break;
}
}
}
if (need_config) {
err = bpf_object__read_kernel_config(obj, config_path, data);
err = bpf_object__read_kconfig_file(obj, data);
if (err)
return -EINVAL;
}
Expand Down Expand Up @@ -4818,7 +4862,7 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr)
obj->loaded = true;

err = bpf_object__probe_caps(obj);
err = err ? : bpf_object__resolve_externs(obj, obj->kconfig_path);
err = err ? : bpf_object__resolve_externs(obj, obj->kconfig);
err = err ? : bpf_object__sanitize_and_load_btf(obj);
err = err ? : bpf_object__sanitize_maps(obj);
err = err ? : bpf_object__create_maps(obj);
Expand Down Expand Up @@ -5412,7 +5456,7 @@ void bpf_object__close(struct bpf_object *obj)
zfree(&map->pin_path);
}

zfree(&obj->kconfig_path);
zfree(&obj->kconfig);
zfree(&obj->externs);
obj->nr_extern = 0;

Expand Down
8 changes: 4 additions & 4 deletions tools/lib/bpf/libbpf.h
Original file line number Diff line number Diff line change
Expand Up @@ -85,12 +85,12 @@ struct bpf_object_open_opts {
*/
const char *pin_root_path;
__u32 attach_prog_fd;
/* kernel config file path override (for CONFIG_ externs); can point
* to either uncompressed text file or .gz file
/* Additional kernel config content that augments and overrides
* system Kconfig for CONFIG_xxx externs.
*/
const char *kconfig_path;
const char *kconfig;
};
#define bpf_object_open_opts__last_field kconfig_path
#define bpf_object_open_opts__last_field kconfig

LIBBPF_API struct bpf_object *bpf_object__open(const char *path);
LIBBPF_API struct bpf_object *
Expand Down
32 changes: 4 additions & 28 deletions tools/testing/selftests/bpf/prog_tests/core_extern.c
Original file line number Diff line number Diff line change
Expand Up @@ -23,19 +23,13 @@ static uint32_t get_kernel_version(void)
static struct test_case {
const char *name;
const char *cfg;
const char *cfg_path;
bool fails;
struct test_core_extern__data data;
} test_cases[] = {
{ .name = "default search path", .cfg_path = NULL,
.data = { .bpf_syscall = true } },
{ .name = "/proc/config.gz", .cfg_path = "/proc/config.gz",
.data = { .bpf_syscall = true } },
{ .name = "missing config", .fails = true,
.cfg_path = "/proc/invalid-config.gz" },
{ .name = "default search path", .data = { .bpf_syscall = true } },
{
.name = "custom values",
.cfg = "CONFIG_BPF_SYSCALL=y\n"
.cfg = "CONFIG_BPF_SYSCALL=n\n"
"CONFIG_TRISTATE=m\n"
"CONFIG_BOOL=y\n"
"CONFIG_CHAR=100\n"
Expand All @@ -45,7 +39,7 @@ static struct test_case {
"CONFIG_STR=\"abracad\"\n"
"CONFIG_MISSING=0",
.data = {
.bpf_syscall = true,
.bpf_syscall = false,
.tristate_val = TRI_MODULE,
.bool_val = true,
.char_val = 100,
Expand Down Expand Up @@ -133,30 +127,14 @@ void test_core_extern(void)
int n = sizeof(*skel->data) / sizeof(uint64_t);

for (i = 0; i < ARRAY_SIZE(test_cases); i++) {
char tmp_cfg_path[] = "/tmp/test_core_extern_cfg.XXXXXX";
struct test_case *t = &test_cases[i];
DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts,
.kconfig_path = t->cfg_path,
.kconfig = t->cfg,
);

if (!test__start_subtest(t->name))
continue;

if (t->cfg) {
size_t n = strlen(t->cfg) + 1;
int fd = mkstemp(tmp_cfg_path);
int written;

if (CHECK(fd < 0, "mkstemp", "errno: %d\n", errno))
continue;
printf("using '%s' as config file\n", tmp_cfg_path);
written = write(fd, t->cfg, n);
close(fd);
if (CHECK_FAIL(written != n))
goto cleanup;
opts.kconfig_path = tmp_cfg_path;
}

skel = test_core_extern__open_opts(&opts);
if (CHECK(!skel, "skel_open", "skeleton open failed\n"))
goto cleanup;
Expand Down Expand Up @@ -185,8 +163,6 @@ void test_core_extern(void)
j, exp[j], got[j]);
}
cleanup:
if (t->cfg)
unlink(tmp_cfg_path);
test_core_extern__destroy(skel);
skel = NULL;
}
Expand Down

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