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Commit 47b6cb4d authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
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libbpf: Make kernel feature probing lazy 

Turn libbpf's kernel feature probing into lazily-performed checks. This allows
to skip performing unnecessary feature checks, if a given BPF application
doesn't rely on a particular kernel feature. As we grow number of feature
probes, libbpf might perform less unnecessary syscalls and scale better with
number of feature probes long-term.

By decoupling feature checks from bpf_object, it's also possible to perform
feature probing from libbpf static helpers and low-level APIs, if necessary.
Signed-off-by: default avatarAndrii Nakryiko <andriin@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200818213356.2629020-3-andriin@fb.com
parent 8d708236
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Showing with 86 additions and 64 deletions
tools/lib/bpf/libbpf.c
View file @ 47b6cb4d
......@@ -165,23 +165,26 @@ static inline __u64 ptr_to_u64(const void *ptr)
return (__u64) (unsigned long) ptr;
}
struct bpf_capabilities {
enum kern_feature_id {
/* v4.14: kernel support for program & map names. */
__u32 name:1;
FEAT_PROG_NAME,
/* v5.2: kernel support for global data sections. */
__u32 global_data:1;
FEAT_GLOBAL_DATA,
/* BTF_KIND_FUNC and BTF_KIND_FUNC_PROTO support */
__u32 btf_func:1;
FEAT_BTF_FUNC,
/* BTF_KIND_VAR and BTF_KIND_DATASEC support */
__u32 btf_datasec:1;
/* BPF_F_MMAPABLE is supported for arrays */
__u32 array_mmap:1;
FEAT_BTF_DATASEC,
/* BTF_FUNC_GLOBAL is supported */
__u32 btf_func_global:1;
FEAT_BTF_GLOBAL_FUNC,
/* BPF_F_MMAPABLE is supported for arrays */
FEAT_ARRAY_MMAP,
/* kernel support for expected_attach_type in BPF_PROG_LOAD */
__u32 exp_attach_type:1;
FEAT_EXP_ATTACH_TYPE,
__FEAT_CNT,
};
static bool kernel_supports(enum kern_feature_id feat_id);
enum reloc_type {
RELO_LD64,
RELO_CALL,
......@@ -253,8 +256,6 @@ struct bpf_program {
__u32 func_info_rec_size;
__u32 func_info_cnt;
struct bpf_capabilities *caps;
void *line_info;
__u32 line_info_rec_size;
__u32 line_info_cnt;
......@@ -436,8 +437,6 @@ struct bpf_object {
void *priv;
bpf_object_clear_priv_t clear_priv;
struct bpf_capabilities caps;
char path[];
};
#define obj_elf_valid(o) ((o)->efile.elf)
......@@ -561,7 +560,6 @@ bpf_object__add_program(struct bpf_object *obj, void *data, size_t size,
if (err)
return err;
prog.caps = &obj->caps;
progs = obj->programs;
nr_progs = obj->nr_programs;
......@@ -2340,18 +2338,18 @@ static bool section_have_execinstr(struct bpf_object *obj, int idx)
static bool btf_needs_sanitization(struct bpf_object *obj)
{
bool has_func_global = obj->caps.btf_func_global;
bool has_datasec = obj->caps.btf_datasec;
bool has_func = obj->caps.btf_func;
bool has_func_global = kernel_supports(FEAT_BTF_GLOBAL_FUNC);
bool has_datasec = kernel_supports(FEAT_BTF_DATASEC);
bool has_func = kernel_supports(FEAT_BTF_FUNC);
return !has_func || !has_datasec || !has_func_global;
}
static void bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf)
{
bool has_func_global = obj->caps.btf_func_global;
bool has_datasec = obj->caps.btf_datasec;
bool has_func = obj->caps.btf_func;
bool has_func_global = kernel_supports(FEAT_BTF_GLOBAL_FUNC);
bool has_datasec = kernel_supports(FEAT_BTF_DATASEC);
bool has_func = kernel_supports(FEAT_BTF_FUNC);
struct btf_type *t;
int i, j, vlen;
......@@ -3433,8 +3431,7 @@ bpf_object__probe_loading(struct bpf_object *obj)
return 0;
}
static int
bpf_object__probe_name(struct bpf_object *obj)
static int probe_kern_prog_name(void)
{
struct bpf_load_program_attr attr;
struct bpf_insn insns[] = {
......@@ -3453,15 +3450,14 @@ bpf_object__probe_name(struct bpf_object *obj)
attr.name = "test";
ret = bpf_load_program_xattr(&attr, NULL, 0);
if (ret >= 0) {
obj->caps.name = 1;
close(ret);
return 1;
}
return 0;
}
static int
bpf_object__probe_global_data(struct bpf_object *obj)
static int probe_kern_global_data(void)
{
struct bpf_load_program_attr prg_attr;
struct bpf_create_map_attr map_attr;
......@@ -3498,16 +3494,16 @@ bpf_object__probe_global_data(struct bpf_object *obj)
prg_attr.license = "GPL";
ret = bpf_load_program_xattr(&prg_attr, NULL, 0);
close(map);
if (ret >= 0) {
obj->caps.global_data = 1;
close(ret);
return 1;
}
close(map);
return 0;
}
static int bpf_object__probe_btf_func(struct bpf_object *obj)
static int probe_kern_btf_func(void)
{
static const char strs[] = "\0int\0x\0a";
/* void x(int a) {} */
......@@ -3525,7 +3521,6 @@ static int bpf_object__probe_btf_func(struct bpf_object *obj)
btf_fd = libbpf__load_raw_btf((char *)types, sizeof(types),
strs, sizeof(strs));
if (btf_fd >= 0) {
obj->caps.btf_func = 1;
close(btf_fd);
return 1;
}
......@@ -3533,7 +3528,7 @@ static int bpf_object__probe_btf_func(struct bpf_object *obj)
return 0;
}
static int bpf_object__probe_btf_func_global(struct bpf_object *obj)
static int probe_kern_btf_func_global(void)
{
static const char strs[] = "\0int\0x\0a";
/* static void x(int a) {} */
......@@ -3551,7 +3546,6 @@ static int bpf_object__probe_btf_func_global(struct bpf_object *obj)
btf_fd = libbpf__load_raw_btf((char *)types, sizeof(types),
strs, sizeof(strs));
if (btf_fd >= 0) {
obj->caps.btf_func_global = 1;
close(btf_fd);
return 1;
}
......@@ -3559,7 +3553,7 @@ static int bpf_object__probe_btf_func_global(struct bpf_object *obj)
return 0;
}
static int bpf_object__probe_btf_datasec(struct bpf_object *obj)
static int probe_kern_btf_datasec(void)
{
static const char strs[] = "\0x\0.data";
/* static int a; */
......@@ -3578,7 +3572,6 @@ static int bpf_object__probe_btf_datasec(struct bpf_object *obj)
btf_fd = libbpf__load_raw_btf((char *)types, sizeof(types),
strs, sizeof(strs));
if (btf_fd >= 0) {
obj->caps.btf_datasec = 1;
close(btf_fd);
return 1;
}
......@@ -3586,7 +3579,7 @@ static int bpf_object__probe_btf_datasec(struct bpf_object *obj)
return 0;
}
static int bpf_object__probe_array_mmap(struct bpf_object *obj)
static int probe_kern_array_mmap(void)
{
struct bpf_create_map_attr attr = {
.map_type = BPF_MAP_TYPE_ARRAY,
......@@ -3599,16 +3592,13 @@ static int bpf_object__probe_array_mmap(struct bpf_object *obj)
fd = bpf_create_map_xattr(&attr);
if (fd >= 0) {
obj->caps.array_mmap = 1;
close(fd);
return 1;
}
return 0;
}
static int
bpf_object__probe_exp_attach_type(struct bpf_object *obj)
static int probe_kern_exp_attach_type(void)
{
struct bpf_load_program_attr attr;
struct bpf_insn insns[] = {
......@@ -3631,34 +3621,67 @@ bpf_object__probe_exp_attach_type(struct bpf_object *obj)
fd = bpf_load_program_xattr(&attr, NULL, 0);
if (fd >= 0) {
obj->caps.exp_attach_type = 1;
close(fd);
return 1;
}
return 0;
}
static int
bpf_object__probe_caps(struct bpf_object *obj)
{
int (*probe_fn[])(struct bpf_object *obj) = {
bpf_object__probe_name,
bpf_object__probe_global_data,
bpf_object__probe_btf_func,
bpf_object__probe_btf_func_global,
bpf_object__probe_btf_datasec,
bpf_object__probe_array_mmap,
bpf_object__probe_exp_attach_type,
};
int i, ret;
enum kern_feature_result {
FEAT_UNKNOWN = 0,
FEAT_SUPPORTED = 1,
FEAT_MISSING = 2,
};
for (i = 0; i < ARRAY_SIZE(probe_fn); i++) {
ret = probe_fn[i](obj);
if (ret < 0)
pr_debug("Probe #%d failed with %d.\n", i, ret);
typedef int (*feature_probe_fn)(void);
static struct kern_feature_desc {
const char *desc;
feature_probe_fn probe;
enum kern_feature_result res;
} feature_probes[__FEAT_CNT] = {
[FEAT_PROG_NAME] = {
"BPF program name", probe_kern_prog_name,
},
[FEAT_GLOBAL_DATA] = {
"global variables", probe_kern_global_data,
},
[FEAT_BTF_FUNC] = {
"BTF functions", probe_kern_btf_func,
},
[FEAT_BTF_GLOBAL_FUNC] = {
"BTF global function", probe_kern_btf_func_global,
},
[FEAT_BTF_DATASEC] = {
"BTF data section and variable", probe_kern_btf_datasec,
},
[FEAT_ARRAY_MMAP] = {
"ARRAY map mmap()", probe_kern_array_mmap,
},
[FEAT_EXP_ATTACH_TYPE] = {
"BPF_PROG_LOAD expected_attach_type attribute",
probe_kern_exp_attach_type,
},
};
static bool kernel_supports(enum kern_feature_id feat_id)
{
struct kern_feature_desc *feat = &feature_probes[feat_id];
int ret;
if (READ_ONCE(feat->res) == FEAT_UNKNOWN) {
ret = feat->probe();
if (ret > 0) {
WRITE_ONCE(feat->res, FEAT_SUPPORTED);
} else if (ret == 0) {
WRITE_ONCE(feat->res, FEAT_MISSING);
} else {
pr_warn("Detection of kernel %s support failed: %d\n", feat->desc, ret);
WRITE_ONCE(feat->res, FEAT_MISSING);
}
}
return 0;
return READ_ONCE(feat->res) == FEAT_SUPPORTED;
}
static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd)
......@@ -3760,7 +3783,7 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map)
memset(&create_attr, 0, sizeof(create_attr));
if (obj->caps.name)
if (kernel_supports(FEAT_PROG_NAME))
create_attr.name = map->name;
create_attr.map_ifindex = map->map_ifindex;
create_attr.map_type = def->type;
......@@ -5364,12 +5387,12 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
memset(&load_attr, 0, sizeof(struct bpf_load_program_attr));
load_attr.prog_type = prog->type;
/* old kernels might not support specifying expected_attach_type */
if (!prog->caps->exp_attach_type && prog->sec_def &&
if (!kernel_supports(FEAT_EXP_ATTACH_TYPE) && prog->sec_def &&
prog->sec_def->is_exp_attach_type_optional)
load_attr.expected_attach_type = 0;
else
load_attr.expected_attach_type = prog->expected_attach_type;
if (prog->caps->name)
if (kernel_supports(FEAT_PROG_NAME))
load_attr.name = prog->name;
load_attr.insns = insns;
load_attr.insns_cnt = insns_cnt;
......@@ -5387,7 +5410,7 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
}
/* specify func_info/line_info only if kernel supports them */
btf_fd = bpf_object__btf_fd(prog->obj);
if (btf_fd >= 0 && prog->obj->caps.btf_func) {
if (btf_fd >= 0 && kernel_supports(FEAT_BTF_FUNC)) {
load_attr.prog_btf_fd = btf_fd;
load_attr.func_info = prog->func_info;
load_attr.func_info_rec_size = prog->func_info_rec_size;
......@@ -5750,11 +5773,11 @@ static int bpf_object__sanitize_maps(struct bpf_object *obj)
bpf_object__for_each_map(m, obj) {
if (!bpf_map__is_internal(m))
continue;
if (!obj->caps.global_data) {
if (!kernel_supports(FEAT_GLOBAL_DATA)) {
pr_warn("kernel doesn't support global data\n");
return -ENOTSUP;
}
if (!obj->caps.array_mmap)
if (!kernel_supports(FEAT_ARRAY_MMAP))
m->def.map_flags ^= BPF_F_MMAPABLE;
}
......@@ -5904,7 +5927,6 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr)
}
err = bpf_object__probe_loading(obj);
err = err ? : bpf_object__probe_caps(obj);
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);
......
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