libbpf: Deprecate bpf_prog_load_xattr() API

bpf_prog_load_xattr() is high-level API that's named as a low-level
BPF_PROG_LOAD wrapper APIs, but it actually operates on struct
bpf_object. It's badly and confusingly misnamed as it will load all the
progs insige bpf_object, returning prog_fd of the very first BPF
program. It also has a bunch of ad-hoc things like log_level override,
map_ifindex auto-setting, etc. All this can be expressed more explicitly
and cleanly through existing libbpf APIs. This patch marks
bpf_prog_load_xattr() for deprecation in libbpf v0.8 ([0]).

  [0] Closes: https://github.com/libbpf/libbpf/issues/308

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211201232824.3166325-10-andrii@kernel.org

tools/lib/bpf/libbpf.h

@@ -682,6 +682,7 @@ struct bpf_prog_load_attr {
 	int prog_flags;
 };
 
+LIBBPF_DEPRECATED_SINCE(0, 8, "use bpf_object__open() and bpf_object__load() instead")
 LIBBPF_API int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr,
 				   struct bpf_object **pobj, int *prog_fd);
 LIBBPF_DEPRECATED_SINCE(0, 7, "use bpf_object__open() and bpf_object__load() instead")

tools/lib/bpf/libbpf_common.h

@@ -40,6 +40,11 @@
 #else
 #define __LIBBPF_MARK_DEPRECATED_0_7(X)
 #endif
+#if __LIBBPF_CURRENT_VERSION_GEQ(0, 8)
+#define __LIBBPF_MARK_DEPRECATED_0_8(X) X
+#else
+#define __LIBBPF_MARK_DEPRECATED_0_8(X)
+#endif
 
 /* This set of internal macros allows to do "function overloading" based on
  * number of arguments provided by used in backwards-compatible way during the