libbpf: Split bpf object load into prepare/load

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 <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

1 files changed, 13 insertions, 0 deletions

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 3020ee45303a..e0605403f977 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -242,6 +242,19 @@ 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
  * **bpf_object__open*()** APIs