[PATCH bpf-next v3 6/8] libbpf: prepare deprecation of btf__get_from_id(), btf__load()

[Quentin Monnet <quentin@isovalent.com>]

Introduce a macro LIBBPF_DEPRECATED_SINCE(major, minor, message) to
prepare the deprecation of two API functions. This macro mark the
functions as deprecated when libbpf's version reaches the values passed
as an argument.

Prepare deprecation for btf__get_from_id() and btf__load(), respectively
replaced by btf__load_from_kernel_by_id() and btf__load_into_kernel(),
for version 0.6 of the library.

References:

- https://github.com/libbpf/libbpf/issues/278
- https://github.com/libbpf/libbpf/wiki/Libbpf:-the-road-to-v1.0#btfh-apis

Side notes:

- Because of the constraints from the preprocessor, we have to write a
  few lines of macro magic for each version used to prepare deprecation
  (0.6 for now).
- Checkpatch complains about the absence of parentheses around the
  definition for LIBBPF_DEPRECATED_SINCE, but the compiler profusely
  complains if we attempt to add them.

Signed-off-by: Quentin Monnet <quentin@isovalent.com>
---
 tools/lib/bpf/Makefile        |  3 +++
 tools/lib/bpf/btf.h           |  2 ++
 tools/lib/bpf/libbpf_common.h | 19 +++++++++++++++++++
 3 files changed, 24 insertions(+)

diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index ec14aa725bb0..095d5dc30d50 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -8,6 +8,7 @@ LIBBPF_VERSION := $(shell \
 	grep -oE '^LIBBPF_([0-9.]+)' libbpf.map | \
 	sort -rV | head -n1 | cut -d'_' -f2)
 LIBBPF_MAJOR_VERSION := $(firstword $(subst ., ,$(LIBBPF_VERSION)))
+LIBBPF_MINOR_VERSION := $(firstword $(subst ., ,$(subst $(LIBBPF_MAJOR_VERSION)., ,$(LIBBPF_VERSION))))
 
 MAKEFLAGS += --no-print-directory
 
@@ -86,6 +87,8 @@ override CFLAGS += -Werror -Wall
 override CFLAGS += $(INCLUDES)
 override CFLAGS += -fvisibility=hidden
 override CFLAGS += -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64
+override CFLAGS += -DLIBBPF_MAJOR_VERSION=$(LIBBPF_MAJOR_VERSION)
+override CFLAGS += -DLIBBPF_MINOR_VERSION=$(LIBBPF_MINOR_VERSION)
 
 # flags specific for shared library
 SHLIB_FLAGS := -DSHARED -fPIC
diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
index 698afde03c2e..a6039ca66895 100644
--- a/tools/lib/bpf/btf.h
+++ b/tools/lib/bpf/btf.h
@@ -44,9 +44,11 @@ LIBBPF_API struct btf *btf__parse_elf_split(const char *path, struct btf *base_b
 LIBBPF_API struct btf *btf__parse_raw(const char *path);
 LIBBPF_API struct btf *btf__parse_raw_split(const char *path, struct btf *base_btf);
 LIBBPF_API struct btf *btf__load_from_kernel_by_id(__u32 id);
+LIBBPF_DEPRECATED_SINCE(0, 6, "use btf__load_from_kernel_by_id instead")
 LIBBPF_API int btf__get_from_id(__u32 id, struct btf **btf);
 
 LIBBPF_API int btf__finalize_data(struct bpf_object *obj, struct btf *btf);
+LIBBPF_DEPRECATED_SINCE(0, 6, "use btf__load_into_kernel instead")
 LIBBPF_API int btf__load(struct btf *btf);
 LIBBPF_API int btf__load_into_kernel(struct btf *btf);
 LIBBPF_API __s32 btf__find_by_name(const struct btf *btf,
diff --git a/tools/lib/bpf/libbpf_common.h b/tools/lib/bpf/libbpf_common.h
index 947d8bd8a7bb..7218d6156ed7 100644
--- a/tools/lib/bpf/libbpf_common.h
+++ b/tools/lib/bpf/libbpf_common.h
@@ -17,6 +17,25 @@
 
 #define LIBBPF_DEPRECATED(msg) __attribute__((deprecated(msg)))
 
+#define __LIBBPF_GET_VERSION(major, minor) (((major) << 8) + (minor))
+#define __LIBBPF_CURRENT_VERSION					    \
+	__LIBBPF_GET_VERSION(LIBBPF_MAJOR_VERSION, LIBBPF_MINOR_VERSION)
+#define __LIBBPF_CURRENT_VERSION_GEQ(major, minor)			    \
+	(__LIBBPF_CURRENT_VERSION >= __LIBBPF_GET_VERSION(major, minor))
+/* Add checks for other versions below when planning deprecation of API symbols
+ * with the LIBBPF_DEPRECATED_SINCE macro.
+ */
+#if __LIBBPF_CURRENT_VERSION_GEQ(0, 6)
+#define __LIBBPF_MARK_DEPRECATED_0_6(X) X
+#else
+#define __LIBBPF_MARK_DEPRECATED_0_6(X)
+#endif
+
+/* Mark a symbol as deprecated when libbpf version is >= {major}.{minor} */
+#define LIBBPF_DEPRECATED_SINCE(major, minor, msg)			    \
+	__LIBBPF_MARK_DEPRECATED_ ## major ## _ ## minor		    \
+		(LIBBPF_DEPRECATED("v" # major "." # minor "+, " msg))
+
 /* Helper macro to declare and initialize libbpf options struct
  *
  * This dance with uninitialized declaration, followed by memset to zero,
-- 
2.30.2