From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

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@kernel.org>
Reviewed-by: Alan Maguire <redacted>
---
 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().
 Changes in v4:
  - Use a stack for searching in anonymous members instead of nested call.
---
 include/linux/btf.h |    3 +++
 kernel/bpf/btf.c    |   40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 43 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..8d81a4ffa67b 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c

@@ -958,6 +958,46 @@ const struct btf_param *btf_get_func_param(const struct btf_type *func_proto, s3
                return NULL;
 }

+#define BTF_ANON_STACK_MAX     16
+
+/*
+ * 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_type *anon_stack[BTF_ANON_STACK_MAX];
+       const struct btf_member *member;
+       const char *name;
+       int i, top = 0;
+
+retry:
+       if (!btf_type_is_struct(type))
+               return ERR_PTR(-EINVAL);
+
+       for_each_member(i, type, member) {
+               if (!member->name_off) {
+                       /* Anonymous union/struct: push it for later use */
+                       type = btf_type_skip_modifiers(btf, member->type, NULL);
+                       if (type && top < BTF_ANON_STACK_MAX)
+                               anon_stack[top++] = type;
+               } else {
+                       name = btf_name_by_offset(btf, member->name_off);
+                       if (name && !strcmp(member_name, name))
+                               return member;
+               }
+       }
+       if (top > 0) {
+               /* Pop from the anonymous stack and retry */
+               type = anon_stack[--top];
+               goto retry;
+       }