libbpf: Unify low-level BPF_PROG_LOAD APIs into bpf_prog_load()

Add a new unified OPTS-based low-level API for program loading,
bpf_prog_load() ([0]).  bpf_prog_load() accepts few "mandatory"
parameters as input arguments (program type, name, license,
instructions) and all the other optional (as in not required to specify
for all types of BPF programs) fields into struct bpf_prog_load_opts.

This makes all the other non-extensible APIs variant for BPF_PROG_LOAD
obsolete and they are slated for deprecation in libbpf v0.7:
  - bpf_load_program();
  - bpf_load_program_xattr();
  - bpf_verify_program().

Implementation-wise, internal helper libbpf__bpf_prog_load is refactored
to become a public bpf_prog_load() API. struct bpf_prog_load_params used
internally is replaced by public struct bpf_prog_load_opts.

Unfortunately, while conceptually all this is pretty straightforward,
the biggest complication comes from the already existing bpf_prog_load()
*high-level* API, which has nothing to do with BPF_PROG_LOAD command.

We try really hard to have a new API named bpf_prog_load(), though,
because it maps naturally to BPF_PROG_LOAD command.

For that, we rename old bpf_prog_load() into bpf_prog_load_deprecated()
and mark it as COMPAT_VERSION() for shared library users compiled
against old version of libbpf. Statically linked users and shared lib
users compiled against new version of libbpf headers will get "rerouted"
to bpf_prog_deprecated() through a macro helper that decides whether to
use new or old bpf_prog_load() based on number of input arguments (see
___libbpf_overload in libbpf_common.h).

To test that existing
bpf_prog_load()-using code compiles and works as expected, I've compiled
and ran selftests as is. I had to remove (locally) selftest/bpf/Makefile
-Dbpf_prog_load=bpf_prog_test_load hack because it was conflicting with
the macro-based overload approach. I don't expect anyone else to do
something like this in practice, though. This is testing-specific way to
replace bpf_prog_load() calls with special testing variant of it, which
adds extra prog_flags value. After testing I kept this selftests hack,
but ensured that we use a new bpf_prog_load_deprecated name for this.

This patch also marks bpf_prog_load() and bpf_prog_load_xattr() as deprecated.
bpf_object interface has to be used for working with struct bpf_program.
Libbpf doesn't support loading just a bpf_program.

The silver lining is that when we get to libbpf 1.0 all these
complication will be gone and we'll have one clean bpf_prog_load()
low-level API with no backwards compatibility hackery surrounding it.

  [0] Closes: https://github.com/libbpf/libbpf/issues/284

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211103220845.2676888-4-andrii@kernel.org

1 files changed, 70 insertions, 3 deletions

diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index f35146c1d9a9..079cc81ac51e 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -72,6 +72,71 @@ LIBBPF_API int bpf_create_map_in_map(enum bpf_map_type map_type,
 				     int inner_map_fd, int max_entries,
 				     __u32 map_flags);
 
+struct bpf_prog_load_opts {
+	size_t sz; /* size of this struct for forward/backward compatibility */
+
+	/* libbpf can retry BPF_PROG_LOAD command if bpf() syscall returns
+	 * -EAGAIN. This field determines how many attempts libbpf has to
+	 *  make. If not specified, libbpf will use default value of 5.
+	 */
+	int attempts;
+
+	enum bpf_attach_type expected_attach_type;
+	__u32 prog_btf_fd;
+	__u32 prog_flags;
+	__u32 prog_ifindex;
+	__u32 kern_version;
+
+	__u32 attach_btf_id;
+	__u32 attach_prog_fd;
+	__u32 attach_btf_obj_fd;
+
+	const int *fd_array;
+
+	/* .BTF.ext func info data */
+	const void *func_info;
+	__u32 func_info_cnt;
+	__u32 func_info_rec_size;
+
+	/* .BTF.ext line info data */
+	const void *line_info;
+	__u32 line_info_cnt;
+	__u32 line_info_rec_size;
+
+	/* verifier log options */
+	__u32 log_level;
+	__u32 log_size;
+	char *log_buf;
+};
+#define bpf_prog_load_opts__last_field log_buf
+
+LIBBPF_API int bpf_prog_load(enum bpf_prog_type prog_type,
+			     const char *prog_name, const char *license,
+			     const struct bpf_insn *insns, size_t insn_cnt,
+			     const struct bpf_prog_load_opts *opts);
+/* this "specialization" should go away in libbpf 1.0 */
+LIBBPF_API int bpf_prog_load_v0_6_0(enum bpf_prog_type prog_type,
+				    const char *prog_name, const char *license,
+				    const struct bpf_insn *insns, size_t insn_cnt,
+				    const struct bpf_prog_load_opts *opts);
+
+/* This is an elaborate way to not conflict with deprecated bpf_prog_load()
+ * API, defined in libbpf.h. Once we hit libbpf 1.0, all this will be gone.
+ * With this approach, if someone is calling bpf_prog_load() with
+ * 4 arguments, they will use the deprecated API, which keeps backwards
+ * compatibility (both source code and binary). If bpf_prog_load() is called
+ * with 6 arguments, though, it gets redirected to __bpf_prog_load.
+ * So looking forward to libbpf 1.0 when this hack will be gone and
+ * __bpf_prog_load() will be called just bpf_prog_load().
+ */
+#ifndef bpf_prog_load
+#define bpf_prog_load(...) ___libbpf_overload(___bpf_prog_load, __VA_ARGS__)
+#define ___bpf_prog_load4(file, type, pobj, prog_fd) \
+	bpf_prog_load_deprecated(file, type, pobj, prog_fd)
+#define ___bpf_prog_load6(prog_type, prog_name, license, insns, insn_cnt, opts) \
+	bpf_prog_load(prog_type, prog_name, license, insns, insn_cnt, opts)
+#endif /* bpf_prog_load */
+
 struct bpf_load_program_attr {
 	enum bpf_prog_type prog_type;
 	enum bpf_attach_type expected_attach_type;
@@ -103,13 +168,15 @@ struct bpf_load_program_attr {
 
 /* Recommend log buffer size */
 #define BPF_LOG_BUF_SIZE (UINT32_MAX >> 8) /* verifier maximum in kernels <= 5.1 */
-LIBBPF_API int
-bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
-		       char *log_buf, size_t log_buf_sz);
+LIBBPF_DEPRECATED_SINCE(0, 7, "use bpf_prog_load() instead")
+LIBBPF_API int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
+				      char *log_buf, size_t log_buf_sz);
+LIBBPF_DEPRECATED_SINCE(0, 7, "use bpf_prog_load() instead")
 LIBBPF_API int bpf_load_program(enum bpf_prog_type type,
 				const struct bpf_insn *insns, size_t insns_cnt,
 				const char *license, __u32 kern_version,
 				char *log_buf, size_t log_buf_sz);
+LIBBPF_DEPRECATED_SINCE(0, 7, "use bpf_prog_load() instead")
 LIBBPF_API int bpf_verify_program(enum bpf_prog_type type,
 				  const struct bpf_insn *insns,
 				  size_t insns_cnt, __u32 prog_flags,