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: Andrii Nakryiko <andriin@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20200818213356.2629020-3-andriin@fb.com
This commit is contained in:
Andrii Nakryiko
Alexei Starovoitov
parent
8d70823605
commit
47b6cb4d0a
@ -165,23 +165,26 @@ static inline __u64 ptr_to_u64(const void *ptr)
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return (__u64) (unsigned long) ptr;
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}
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struct bpf_capabilities {
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enum kern_feature_id {
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/* v4.14: kernel support for program & map names. */
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__u32 name:1;
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FEAT_PROG_NAME,
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/* v5.2: kernel support for global data sections. */
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__u32 global_data:1;
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FEAT_GLOBAL_DATA,
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/* BTF_KIND_FUNC and BTF_KIND_FUNC_PROTO support */
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__u32 btf_func:1;
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FEAT_BTF_FUNC,
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/* BTF_KIND_VAR and BTF_KIND_DATASEC support */
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__u32 btf_datasec:1;
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/* BPF_F_MMAPABLE is supported for arrays */
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__u32 array_mmap:1;
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FEAT_BTF_DATASEC,
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/* BTF_FUNC_GLOBAL is supported */
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__u32 btf_func_global:1;
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FEAT_BTF_GLOBAL_FUNC,
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/* BPF_F_MMAPABLE is supported for arrays */
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FEAT_ARRAY_MMAP,
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/* kernel support for expected_attach_type in BPF_PROG_LOAD */
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__u32 exp_attach_type:1;
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FEAT_EXP_ATTACH_TYPE,
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__FEAT_CNT,
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};
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static bool kernel_supports(enum kern_feature_id feat_id);
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enum reloc_type {
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RELO_LD64,
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RELO_CALL,
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@ -253,8 +256,6 @@ struct bpf_program {
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__u32 func_info_rec_size;
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__u32 func_info_cnt;
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struct bpf_capabilities *caps;
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void *line_info;
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__u32 line_info_rec_size;
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__u32 line_info_cnt;
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@ -436,8 +437,6 @@ struct bpf_object {
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void *priv;
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bpf_object_clear_priv_t clear_priv;
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struct bpf_capabilities caps;
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char path[];
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};
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#define obj_elf_valid(o) ((o)->efile.elf)
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@ -561,7 +560,6 @@ bpf_object__add_program(struct bpf_object *obj, void *data, size_t size,
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if (err)
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return err;
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prog.caps = &obj->caps;
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progs = obj->programs;
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nr_progs = obj->nr_programs;
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@ -2340,18 +2338,18 @@ static bool section_have_execinstr(struct bpf_object *obj, int idx)
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static bool btf_needs_sanitization(struct bpf_object *obj)
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{
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bool has_func_global = obj->caps.btf_func_global;
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bool has_datasec = obj->caps.btf_datasec;
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bool has_func = obj->caps.btf_func;
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bool has_func_global = kernel_supports(FEAT_BTF_GLOBAL_FUNC);
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bool has_datasec = kernel_supports(FEAT_BTF_DATASEC);
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bool has_func = kernel_supports(FEAT_BTF_FUNC);
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return !has_func || !has_datasec || !has_func_global;
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}
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static void bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf)
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{
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bool has_func_global = obj->caps.btf_func_global;
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bool has_datasec = obj->caps.btf_datasec;
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bool has_func = obj->caps.btf_func;
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bool has_func_global = kernel_supports(FEAT_BTF_GLOBAL_FUNC);
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bool has_datasec = kernel_supports(FEAT_BTF_DATASEC);
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bool has_func = kernel_supports(FEAT_BTF_FUNC);
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struct btf_type *t;
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int i, j, vlen;
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@ -3433,8 +3431,7 @@ bpf_object__probe_loading(struct bpf_object *obj)
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return 0;
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}
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static int
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bpf_object__probe_name(struct bpf_object *obj)
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static int probe_kern_prog_name(void)
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{
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struct bpf_load_program_attr attr;
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struct bpf_insn insns[] = {
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@ -3453,15 +3450,14 @@ bpf_object__probe_name(struct bpf_object *obj)
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attr.name = "test";
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ret = bpf_load_program_xattr(&attr, NULL, 0);
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if (ret >= 0) {
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obj->caps.name = 1;
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close(ret);
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return 1;
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}
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return 0;
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}
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static int
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bpf_object__probe_global_data(struct bpf_object *obj)
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static int probe_kern_global_data(void)
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{
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struct bpf_load_program_attr prg_attr;
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struct bpf_create_map_attr map_attr;
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@ -3498,16 +3494,16 @@ bpf_object__probe_global_data(struct bpf_object *obj)
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prg_attr.license = "GPL";
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ret = bpf_load_program_xattr(&prg_attr, NULL, 0);
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close(map);
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if (ret >= 0) {
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obj->caps.global_data = 1;
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close(ret);
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return 1;
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}
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close(map);
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return 0;
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}
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static int bpf_object__probe_btf_func(struct bpf_object *obj)
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static int probe_kern_btf_func(void)
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{
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static const char strs[] = "\0int\0x\0a";
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/* void x(int a) {} */
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@ -3525,7 +3521,6 @@ static int bpf_object__probe_btf_func(struct bpf_object *obj)
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btf_fd = libbpf__load_raw_btf((char *)types, sizeof(types),
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strs, sizeof(strs));
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if (btf_fd >= 0) {
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obj->caps.btf_func = 1;
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close(btf_fd);
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return 1;
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}
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@ -3533,7 +3528,7 @@ static int bpf_object__probe_btf_func(struct bpf_object *obj)
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return 0;
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}
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static int bpf_object__probe_btf_func_global(struct bpf_object *obj)
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static int probe_kern_btf_func_global(void)
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{
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static const char strs[] = "\0int\0x\0a";
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/* static void x(int a) {} */
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@ -3551,7 +3546,6 @@ static int bpf_object__probe_btf_func_global(struct bpf_object *obj)
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btf_fd = libbpf__load_raw_btf((char *)types, sizeof(types),
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strs, sizeof(strs));
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if (btf_fd >= 0) {
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obj->caps.btf_func_global = 1;
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close(btf_fd);
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return 1;
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}
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@ -3559,7 +3553,7 @@ static int bpf_object__probe_btf_func_global(struct bpf_object *obj)
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return 0;
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}
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static int bpf_object__probe_btf_datasec(struct bpf_object *obj)
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static int probe_kern_btf_datasec(void)
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{
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static const char strs[] = "\0x\0.data";
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/* static int a; */
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@ -3578,7 +3572,6 @@ static int bpf_object__probe_btf_datasec(struct bpf_object *obj)
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btf_fd = libbpf__load_raw_btf((char *)types, sizeof(types),
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strs, sizeof(strs));
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if (btf_fd >= 0) {
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obj->caps.btf_datasec = 1;
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close(btf_fd);
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return 1;
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}
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@ -3586,7 +3579,7 @@ static int bpf_object__probe_btf_datasec(struct bpf_object *obj)
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return 0;
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}
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static int bpf_object__probe_array_mmap(struct bpf_object *obj)
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static int probe_kern_array_mmap(void)
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{
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struct bpf_create_map_attr attr = {
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.map_type = BPF_MAP_TYPE_ARRAY,
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@ -3599,16 +3592,13 @@ static int bpf_object__probe_array_mmap(struct bpf_object *obj)
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fd = bpf_create_map_xattr(&attr);
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if (fd >= 0) {
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obj->caps.array_mmap = 1;
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close(fd);
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return 1;
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}
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return 0;
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}
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static int
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bpf_object__probe_exp_attach_type(struct bpf_object *obj)
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static int probe_kern_exp_attach_type(void)
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{
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struct bpf_load_program_attr attr;
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struct bpf_insn insns[] = {
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@ -3631,34 +3621,67 @@ bpf_object__probe_exp_attach_type(struct bpf_object *obj)
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fd = bpf_load_program_xattr(&attr, NULL, 0);
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if (fd >= 0) {
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obj->caps.exp_attach_type = 1;
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close(fd);
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return 1;
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}
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return 0;
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}
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static int
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bpf_object__probe_caps(struct bpf_object *obj)
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{
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int (*probe_fn[])(struct bpf_object *obj) = {
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bpf_object__probe_name,
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bpf_object__probe_global_data,
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bpf_object__probe_btf_func,
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bpf_object__probe_btf_func_global,
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bpf_object__probe_btf_datasec,
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bpf_object__probe_array_mmap,
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bpf_object__probe_exp_attach_type,
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};
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int i, ret;
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enum kern_feature_result {
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FEAT_UNKNOWN = 0,
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FEAT_SUPPORTED = 1,
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FEAT_MISSING = 2,
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};
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for (i = 0; i < ARRAY_SIZE(probe_fn); i++) {
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ret = probe_fn[i](obj);
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if (ret < 0)
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pr_debug("Probe #%d failed with %d.\n", i, ret);
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typedef int (*feature_probe_fn)(void);
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static struct kern_feature_desc {
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const char *desc;
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feature_probe_fn probe;
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enum kern_feature_result res;
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} feature_probes[__FEAT_CNT] = {
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[FEAT_PROG_NAME] = {
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"BPF program name", probe_kern_prog_name,
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},
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[FEAT_GLOBAL_DATA] = {
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"global variables", probe_kern_global_data,
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},
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[FEAT_BTF_FUNC] = {
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"BTF functions", probe_kern_btf_func,
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},
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[FEAT_BTF_GLOBAL_FUNC] = {
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"BTF global function", probe_kern_btf_func_global,
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},
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[FEAT_BTF_DATASEC] = {
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"BTF data section and variable", probe_kern_btf_datasec,
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},
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[FEAT_ARRAY_MMAP] = {
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"ARRAY map mmap()", probe_kern_array_mmap,
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},
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[FEAT_EXP_ATTACH_TYPE] = {
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"BPF_PROG_LOAD expected_attach_type attribute",
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probe_kern_exp_attach_type,
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},
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};
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static bool kernel_supports(enum kern_feature_id feat_id)
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{
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struct kern_feature_desc *feat = &feature_probes[feat_id];
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int ret;
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if (READ_ONCE(feat->res) == FEAT_UNKNOWN) {
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ret = feat->probe();
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if (ret > 0) {
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WRITE_ONCE(feat->res, FEAT_SUPPORTED);
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} else if (ret == 0) {
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WRITE_ONCE(feat->res, FEAT_MISSING);
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} else {
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pr_warn("Detection of kernel %s support failed: %d\n", feat->desc, ret);
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WRITE_ONCE(feat->res, FEAT_MISSING);
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}
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}
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return 0;
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return READ_ONCE(feat->res) == FEAT_SUPPORTED;
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}
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static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd)
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@ -3760,7 +3783,7 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map)
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memset(&create_attr, 0, sizeof(create_attr));
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if (obj->caps.name)
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if (kernel_supports(FEAT_PROG_NAME))
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create_attr.name = map->name;
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create_attr.map_ifindex = map->map_ifindex;
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create_attr.map_type = def->type;
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@ -5364,12 +5387,12 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
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memset(&load_attr, 0, sizeof(struct bpf_load_program_attr));
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load_attr.prog_type = prog->type;
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/* old kernels might not support specifying expected_attach_type */
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if (!prog->caps->exp_attach_type && prog->sec_def &&
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if (!kernel_supports(FEAT_EXP_ATTACH_TYPE) && prog->sec_def &&
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prog->sec_def->is_exp_attach_type_optional)
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load_attr.expected_attach_type = 0;
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else
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load_attr.expected_attach_type = prog->expected_attach_type;
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if (prog->caps->name)
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if (kernel_supports(FEAT_PROG_NAME))
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load_attr.name = prog->name;
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load_attr.insns = insns;
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load_attr.insns_cnt = insns_cnt;
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@ -5387,7 +5410,7 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
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}
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/* specify func_info/line_info only if kernel supports them */
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btf_fd = bpf_object__btf_fd(prog->obj);
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if (btf_fd >= 0 && prog->obj->caps.btf_func) {
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if (btf_fd >= 0 && kernel_supports(FEAT_BTF_FUNC)) {
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load_attr.prog_btf_fd = btf_fd;
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load_attr.func_info = prog->func_info;
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load_attr.func_info_rec_size = prog->func_info_rec_size;
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@ -5750,11 +5773,11 @@ static int bpf_object__sanitize_maps(struct bpf_object *obj)
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bpf_object__for_each_map(m, obj) {
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if (!bpf_map__is_internal(m))
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continue;
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if (!obj->caps.global_data) {
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if (!kernel_supports(FEAT_GLOBAL_DATA)) {
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pr_warn("kernel doesn't support global data\n");
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return -ENOTSUP;
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}
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if (!obj->caps.array_mmap)
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if (!kernel_supports(FEAT_ARRAY_MMAP))
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m->def.map_flags ^= BPF_F_MMAPABLE;
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}
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@ -5904,7 +5927,6 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr)
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}
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err = bpf_object__probe_loading(obj);
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err = err ? : bpf_object__probe_caps(obj);
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err = err ? : bpf_object__resolve_externs(obj, obj->kconfig);
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err = err ? : bpf_object__sanitize_and_load_btf(obj);
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err = err ? : bpf_object__sanitize_maps(obj);
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