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libbpf: Split bpf object load into prepare/load

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Introduce bpf_object__prepare API: additional intermediate preparation
step that performs ELF processing, relocations, prepares final state of
BPF program instructions (accessible with bpf_program__insns()), creates
and (potentially) pins maps, and stops short of loading BPF programs.

We anticipate few use cases for this API, such as:
* Use prepare to initialize bpf_token, without loading freplace
programs, unlocking possibility to lookup BTF of other programs.
* Execute prepare to obtain finalized BPF program instructions without
loading programs, enabling tools like veristat to process one program at
a time, without incurring cost of ELF parsing and processing.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250303135752.158343-4-mykyta.yatsenko5@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Mykyta Yatsenko 2025-03-03 13:57:51 +00:00 committed by Alexei Starovoitov
parent 9a9e347835
commit 1315c28ed8
3 changed files with 118 additions and 44 deletions
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148
tools/lib/bpf/libbpf.c
View File

@ -7901,13 +7901,6 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level)
size_t i;
int err;
for (i = 0; i < obj->nr_programs; i++) {
prog = &obj->programs[i];
err = bpf_object__sanitize_prog(obj, prog);
if (err)
return err;
}
for (i = 0; i < obj->nr_programs; i++) {
prog = &obj->programs[i];
if (prog_is_subprog(obj, prog))
@ -7933,6 +7926,21 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level)
return 0;
}
static int bpf_object_prepare_progs(struct bpf_object *obj)
{
struct bpf_program *prog;
size_t i;
int err;
for (i = 0; i < obj->nr_programs; i++) {
prog = &obj->programs[i];
err = bpf_object__sanitize_prog(obj, prog);
if (err)
return err;
}
return 0;
}
static const struct bpf_sec_def *find_sec_def(const char *sec_name);
static int bpf_object_init_progs(struct bpf_object *obj, const struct bpf_object_open_opts *opts)
@ -8549,9 +8557,72 @@ static int bpf_object_prepare_struct_ops(struct bpf_object *obj)
return 0;
}
static void bpf_object_unpin(struct bpf_object *obj)
{
int i;
/* unpin any maps that were auto-pinned during load */
for (i = 0; i < obj->nr_maps; i++)
if (obj->maps[i].pinned && !obj->maps[i].reused)
bpf_map__unpin(&obj->maps[i], NULL);
}
static void bpf_object_post_load_cleanup(struct bpf_object *obj)
{
int i;
/* clean up fd_array */
zfree(&obj->fd_array);
/* clean up module BTFs */
for (i = 0; i < obj->btf_module_cnt; i++) {
close(obj->btf_modules[i].fd);
btf__free(obj->btf_modules[i].btf);
free(obj->btf_modules[i].name);
}
obj->btf_module_cnt = 0;
zfree(&obj->btf_modules);
/* clean up vmlinux BTF */
btf__free(obj->btf_vmlinux);
obj->btf_vmlinux = NULL;
}
static int bpf_object_prepare(struct bpf_object *obj, const char *target_btf_path)
{
int err;
if (obj->state >= OBJ_PREPARED) {
pr_warn("object '%s': prepare loading can't be attempted twice\n", obj->name);
return -EINVAL;
}
err = bpf_object_prepare_token(obj);
err = err ? : bpf_object__probe_loading(obj);
err = err ? : bpf_object__load_vmlinux_btf(obj, false);
err = err ? : bpf_object__resolve_externs(obj, obj->kconfig);
err = err ? : bpf_object__sanitize_maps(obj);
err = err ? : bpf_object__init_kern_struct_ops_maps(obj);
err = err ? : bpf_object_adjust_struct_ops_autoload(obj);
err = err ? : bpf_object__relocate(obj, obj->btf_custom_path ? : target_btf_path);
err = err ? : bpf_object__sanitize_and_load_btf(obj);
err = err ? : bpf_object__create_maps(obj);
err = err ? : bpf_object_prepare_progs(obj);
if (err) {
bpf_object_unpin(obj);
bpf_object_unload(obj);
obj->state = OBJ_LOADED;
return err;
}
obj->state = OBJ_PREPARED;
return 0;
}
static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const char *target_btf_path)
{
int err, i;
int err;
if (!obj)
return libbpf_err(-EINVAL);
@ -8571,17 +8642,12 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch
return libbpf_err(-LIBBPF_ERRNO__ENDIAN);
}
err = bpf_object_prepare_token(obj);
err = err ? : bpf_object__probe_loading(obj);
err = err ? : bpf_object__load_vmlinux_btf(obj, false);
err = err ? : bpf_object__resolve_externs(obj, obj->kconfig);
err = err ? : bpf_object__sanitize_maps(obj);
err = err ? : bpf_object__init_kern_struct_ops_maps(obj);
err = err ? : bpf_object_adjust_struct_ops_autoload(obj);
err = err ? : bpf_object__relocate(obj, obj->btf_custom_path ? : target_btf_path);
err = err ? : bpf_object__sanitize_and_load_btf(obj);
err = err ? : bpf_object__create_maps(obj);
err = err ? : bpf_object__load_progs(obj, extra_log_level);
if (obj->state < OBJ_PREPARED) {
err = bpf_object_prepare(obj, target_btf_path);
if (err)
return libbpf_err(err);
}
err = bpf_object__load_progs(obj, extra_log_level);
err = err ? : bpf_object_init_prog_arrays(obj);
err = err ? : bpf_object_prepare_struct_ops(obj);
@ -8593,35 +8659,22 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch
err = bpf_gen__finish(obj->gen_loader, obj->nr_programs, obj->nr_maps);
}
/* clean up fd_array */
zfree(&obj->fd_array);
/* clean up module BTFs */
for (i = 0; i < obj->btf_module_cnt; i++) {
close(obj->btf_modules[i].fd);
btf__free(obj->btf_modules[i].btf);
free(obj->btf_modules[i].name);
}
free(obj->btf_modules);
/* clean up vmlinux BTF */
btf__free(obj->btf_vmlinux);
obj->btf_vmlinux = NULL;
bpf_object_post_load_cleanup(obj);
obj->state = OBJ_LOADED; /* doesn't matter if successfully or not */
if (err)
goto out;
if (err) {
bpf_object_unpin(obj);
bpf_object_unload(obj);
pr_warn("failed to load object '%s'\n", obj->path);
return libbpf_err(err);
}
return 0;
out:
/* unpin any maps that were auto-pinned during load */
for (i = 0; i < obj->nr_maps; i++)
if (obj->maps[i].pinned && !obj->maps[i].reused)
bpf_map__unpin(&obj->maps[i], NULL);
}
bpf_object_unload(obj);
pr_warn("failed to load object '%s'\n", obj->path);
return libbpf_err(err);
int bpf_object__prepare(struct bpf_object *obj)
{
return libbpf_err(bpf_object_prepare(obj, NULL));
}
int bpf_object__load(struct bpf_object *obj)
@ -9069,6 +9122,13 @@ void bpf_object__close(struct bpf_object *obj)
if (IS_ERR_OR_NULL(obj))
return;
/*
* if user called bpf_object__prepare() without ever getting to
* bpf_object__load(), we need to clean up stuff that is normally
* cleaned up at the end of loading step
*/
bpf_object_post_load_cleanup(obj);
usdt_manager_free(obj->usdt_man);
obj->usdt_man = NULL;

13
tools/lib/bpf/libbpf.h
View File

@ -241,6 +241,19 @@ LIBBPF_API struct bpf_object *
bpf_object__open_mem(const void *obj_buf, size_t obj_buf_sz,
const struct bpf_object_open_opts *opts);
/**
* @brief **bpf_object__prepare()** prepares BPF object for loading:
* performs ELF processing, relocations, prepares final state of BPF program
* instructions (accessible with bpf_program__insns()), creates and
* (potentially) pins maps. Leaves BPF object in the state ready for program
* loading.
* @param obj Pointer to a valid BPF object instance returned by
* **bpf_object__open*()** API
* @return 0, on success; negative error code, otherwise, error code is
* stored in errno
*/
int bpf_object__prepare(struct bpf_object *obj);
/**
* @brief **bpf_object__load()** loads BPF object into kernel.
* @param obj Pointer to a valid BPF object instance returned by

1
tools/lib/bpf/libbpf.map
View File

@ -436,6 +436,7 @@ LIBBPF_1.6.0 {
bpf_linker__add_buf;
bpf_linker__add_fd;
bpf_linker__new_fd;
bpf_object__prepare;
btf__add_decl_attr;
btf__add_type_attr;
} LIBBPF_1.5.0;