[PATCH v3 3/9] bpf/btf: Add a function to search a member of a struct/union

["Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx>]

From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

Add btf_find_struct_member() API to search a member of a given data structure
or union from the member's name.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
---
 Changes in v3:
  - Remove simple input check.
  - Fix unneeded IS_ERR_OR_NULL() check for btf_type_by_id().
  - Move the code next to btf_get_func_param().
  - Use for_each_member() macro instead of for-loop.
  - Use btf_type_skip_modifiers() instead of btf_type_by_id().
---
 include/linux/btf.h |    3 +++
 kernel/bpf/btf.c    |   35 +++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/include/linux/btf.h b/include/linux/btf.h
index 20e3a07eef8f..4b10d57ceee0 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -226,6 +226,9 @@ const struct btf_type *btf_find_func_proto(const char *func_name,
 					   struct btf **btf_p);
 const struct btf_param *btf_get_func_param(const struct btf_type *func_proto,
 					   s32 *nr);
+const struct btf_member *btf_find_struct_member(struct btf *btf,
+						const struct btf_type *type,
+						const char *member_name);
 
 #define for_each_member(i, struct_type, member)			\
 	for (i = 0, member = btf_type_member(struct_type);	\
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index f7b25c615269..5258870030fc 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -958,6 +958,41 @@ const struct btf_param *btf_get_func_param(const struct btf_type *func_proto, s3
 		return NULL;
 }
 
+/*
+ * Find a member of data structure/union by name and return it.
+ * Return NULL if not found, or -EINVAL if parameter is invalid.
+ */
+const struct btf_member *btf_find_struct_member(struct btf *btf,
+						const struct btf_type *type,
+						const char *member_name)
+{
+	const struct btf_member *member, *ret;
+	const char *name;
+	int i;
+
+	if (!btf_type_is_struct(type))
+		return ERR_PTR(-EINVAL);
+
+	for_each_member(i, type, member) {
+		if (!member->name_off) {
+			/* unnamed member: dig deeper */
+			type = btf_type_skip_modifiers(btf, member->type, NULL);
+			if (type) {
+				ret = btf_find_struct_member(btf, type,
+							     member_name);
+				if (!IS_ERR_OR_NULL(ret))
+					return ret;
+			}
+		} else {
+			name = btf_name_by_offset(btf, member->name_off);
+			if (name && !strcmp(member_name, name))
+				return member;
+		}
+	}
+
+	return NULL;
+}
+
 #define BTF_SHOW_MAX_ITER	10
 
 #define BTF_KIND_BIT(kind)	(1ULL << kind)