[RFC bpf-next 04/13] libbpf: add btf__parse_opts() API for flexible BTF parsing

[Alan Maguire <alan.maguire@oracle.com>]

Options cover existing parsing scenarios (ELF, raw, retrieving
.BTF.ext) and also allow specification of the ELF section name
containing BTF.  This will allow consumers to retrieve BTF from
.BTF.base_ref sections (BTF_BASE_REF_ELF_SEC) also.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 tools/lib/bpf/btf.c      | 24 ++++++++++++++++++------
 tools/lib/bpf/btf.h      | 32 ++++++++++++++++++++++++++++++++
 tools/lib/bpf/libbpf.map |  1 +
 3 files changed, 51 insertions(+), 6 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index f02477af3d79..d43c3eba27e0 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -1084,7 +1084,7 @@ struct btf *btf__new_split(const void *data, __u32 size, struct btf *base_btf)
 	return libbpf_ptr(btf_new(data, size, base_btf));
 }
 
-static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
+static struct btf *btf_parse_elf(const char *path, const char *btf_sec, struct btf *base_btf,
 				 struct btf_ext **btf_ext)
 {
 	Elf_Data *btf_data = NULL, *btf_ext_data = NULL;
@@ -1146,7 +1146,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
 				idx, path);
 			goto done;
 		}
-		if (strcmp(name, BTF_ELF_SEC) == 0) {
+		if (strcmp(name, btf_sec) == 0) {
 			btf_data = elf_getdata(scn, 0);
 			if (!btf_data) {
 				pr_warn("failed to get section(%d, %s) data from %s\n",
@@ -1166,7 +1166,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
 	}
 
 	if (!btf_data) {
-		pr_warn("failed to find '%s' ELF section in %s\n", BTF_ELF_SEC, path);
+		pr_warn("failed to find '%s' ELF section in %s\n", btf_sec, path);
 		err = -ENODATA;
 		goto done;
 	}
@@ -1212,12 +1212,12 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
 
 struct btf *btf__parse_elf(const char *path, struct btf_ext **btf_ext)
 {
-	return libbpf_ptr(btf_parse_elf(path, NULL, btf_ext));
+	return libbpf_ptr(btf_parse_elf(path, BTF_ELF_SEC, NULL, btf_ext));
 }
 
 struct btf *btf__parse_elf_split(const char *path, struct btf *base_btf)
 {
-	return libbpf_ptr(btf_parse_elf(path, base_btf, NULL));
+	return libbpf_ptr(btf_parse_elf(path, BTF_ELF_SEC, base_btf, NULL));
 }
 
 static struct btf *btf_parse_raw(const char *path, struct btf *base_btf)
@@ -1293,6 +1293,18 @@ struct btf *btf__parse_raw_split(const char *path, struct btf *base_btf)
 	return libbpf_ptr(btf_parse_raw(path, base_btf));
 }
 
+struct btf *btf__parse_opts(const char *path, struct btf_parse_opts *opts)
+{
+	if (!OPTS_VALID(opts, btf_parse_opts))
+		return libbpf_err_ptr(-EINVAL);
+	if (opts && !opts->btf_sec)
+		return btf__parse_raw_split(path, opts ? opts->base_btf : NULL);
+	return libbpf_ptr(btf_parse_elf(path,
+					opts ? opts->btf_sec : BTF_ELF_SEC,
+					opts ? opts->base_btf : NULL,
+					opts ? &opts->btf_ext : NULL));
+}
+
 static struct btf *btf_parse(const char *path, struct btf *base_btf, struct btf_ext **btf_ext)
 {
 	struct btf *btf;
@@ -1307,7 +1319,7 @@ static struct btf *btf_parse(const char *path, struct btf *base_btf, struct btf_
 		return btf;
 	if (err != -EPROTO)
 		return ERR_PTR(err);
-	return btf_parse_elf(path, base_btf, btf_ext);
+	return btf_parse_elf(path, BTF_ELF_SEC, base_btf, btf_ext);
 }
 
 struct btf *btf__parse(const char *path, struct btf_ext **btf_ext)
diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
index f2a853d6fa55..c63043520149 100644
--- a/tools/lib/bpf/btf.h
+++ b/tools/lib/bpf/btf.h
@@ -18,6 +18,7 @@ extern "C" {
 
 #define BTF_ELF_SEC ".BTF"
 #define BTF_EXT_ELF_SEC ".BTF.ext"
+#define BTF_BASE_REF_ELF_SEC ".BTF.base_ref"
 #define MAPS_ELF_SEC ".maps"
 
 struct btf;
@@ -129,6 +130,37 @@ 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);
 
+struct btf_parse_opts {
+	size_t sz;
+	/* use base BTF to parse split BTF */
+	struct btf *base_btf;
+	/* retrieve optional .BTF.ext info */
+	struct btf_ext *btf_ext;
+	/* BTF section name */
+	const char *btf_sec;
+        size_t:0;
+};
+
+#define btf_parse_opts__last_field btf_sec
+
+/* @brief **btf__parse_opts()** parses BTF information from either a
+ * raw BTF file (*btf_sec* is NULL) or from the specified BTF section,
+ * also retrieving  .BTF.ext info if *btf_ext* is non-NULL.  If
+ * *base_btf* is specified, use it to parse split BTF from the
+ * specified location.
+ *
+ * @return new BTF object instance which has to be eventually freed with
+ * **btf__free()**
+ *
+ * On error, error-code-encoded-as-pointer is returned, not a NULL. To extract
+ * error code from such a pointer `libbpf_get_error()` should be used. If
+ * `libbpf_set_strict_mode(LIBBPF_STRICT_CLEAN_PTRS)` is enabled, NULL is
+ * returned on error instead. In both cases thread-local `errno` variable is
+ * always set to error code as well.
+ */
+
+LIBBPF_API struct btf *btf__parse_opts(const char *path, struct btf_parse_opts *opts);
+
 LIBBPF_API struct btf *btf__load_vmlinux_btf(void);
 LIBBPF_API struct btf *btf__load_module_btf(const char *module_name, struct btf *vmlinux_btf);
 
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 3d53b1781af1..e9a7cb9c3c5b 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -415,5 +415,6 @@ LIBBPF_1.4.0 {
 		bpf_token_create;
 		btf__new_split;
 		btf__new_split_base_ref;
+		btf__parse_opts;
 		btf_ext__raw_data;
 } LIBBPF_1.3.0;
-- 
2.39.3