[PATCH v4 2/9] bpf/btf: tracing: Move finding func-proto API and getting func-param API to BTF

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

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

Move generic function-proto find API and getting function parameter API
to BTF library code from trace_probe.c. This will avoid redundant efforts
on different feature.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 Changes in v3:
  - Remove perameter check.
  - Fix a typo.
  - Add a type check for btf_get_func_param() and add comment for that.
  - Use bpf_find_btf_id() and add bpf_put().
  - Move the code before btf_show() related code.
---
 include/linux/btf.h        |    4 ++++
 kernel/bpf/btf.c           |   47 +++++++++++++++++++++++++++++++++++++++++
 kernel/trace/trace_probe.c |   50 +++++++++-----------------------------------
 3 files changed, 61 insertions(+), 40 deletions(-)

diff --git a/include/linux/btf.h b/include/linux/btf.h
index dbfe41a09c4b..20e3a07eef8f 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -222,6 +222,10 @@ const struct btf_type *
 btf_resolve_size(const struct btf *btf, const struct btf_type *type,
 		 u32 *type_size);
 const char *btf_type_str(const struct btf_type *t);
+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);
 
 #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 b9b0eb1189bb..f7b25c615269 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -911,6 +911,53 @@ static const struct btf_type *btf_type_skip_qualifiers(const struct btf *btf,
 	return t;
 }
 
+/*
+ * Find a function proto type by name, and return the btf_type with its btf
+ * in *@btf_p. Return NULL if not found.
+ * Note that caller has to call btf_put(*@btf_p) after using the btf_type.
+ */
+const struct btf_type *btf_find_func_proto(const char *func_name, struct btf **btf_p)
+{
+	const struct btf_type *t;
+	s32 id;
+
+	id = bpf_find_btf_id(func_name, BTF_KIND_FUNC, btf_p);
+	if (id < 0)
+		return NULL;
+
+	/* Get BTF_KIND_FUNC type */
+	t = btf_type_by_id(*btf_p, id);
+	if (!t || !btf_type_is_func(t))
+		goto err;
+
+	/* The type of BTF_KIND_FUNC is BTF_KIND_FUNC_PROTO */
+	t = btf_type_by_id(*btf_p, t->type);
+	if (!t || !btf_type_is_func_proto(t))
+		goto err;
+
+	return t;
+err:
+	btf_put(*btf_p);
+	return NULL;
+}
+
+/*
+ * Get function parameter with the number of parameters.
+ * This can return NULL if the function has no parameters.
+ * It can return -EINVAL if the @func_proto is not a function proto type.
+ */
+const struct btf_param *btf_get_func_param(const struct btf_type *func_proto, s32 *nr)
+{
+	if (!btf_type_is_func_proto(func_proto))
+		return ERR_PTR(-EINVAL);
+
+	*nr = btf_type_vlen(func_proto);
+	if (*nr > 0)
+		return (const struct btf_param *)(func_proto + 1);
+	else
+		return NULL;
+}
+
 #define BTF_SHOW_MAX_ITER	10
 
 #define BTF_KIND_BIT(kind)	(1ULL << kind)
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index ecbe28f8d676..21a228d88ebb 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -361,38 +361,6 @@ static const char *type_from_btf_id(struct btf *btf, s32 id)
 	return NULL;
 }
 
-static const struct btf_type *find_btf_func_proto(const char *funcname,
-						  struct btf **btf_p)
-{
-	const struct btf_type *t;
-	struct btf *btf = NULL;
-	s32 id;
-
-	if (!funcname)
-		return ERR_PTR(-EINVAL);
-
-	id = bpf_find_btf_id(funcname, BTF_KIND_FUNC, &btf);
-	if (id <= 0)
-		return ERR_PTR(-ENOENT);
-
-	/* Get BTF_KIND_FUNC type */
-	t = btf_type_by_id(btf, id);
-	if (!t || !btf_type_is_func(t))
-		goto err;
-
-	/* The type of BTF_KIND_FUNC is BTF_KIND_FUNC_PROTO */
-	t = btf_type_by_id(btf, t->type);
-	if (!t || !btf_type_is_func_proto(t))
-		goto err;
-
-	*btf_p = btf;
-	return t;
-
-err:
-	btf_put(btf);
-	return ERR_PTR(-ENOENT);
-}
-
 static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr,
 						   struct btf **btf_p, bool tracepoint)
 {
@@ -403,12 +371,13 @@ static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr
 	if (!funcname || !nr)
 		return ERR_PTR(-EINVAL);
 
-	t = find_btf_func_proto(funcname, &btf);
-	if (IS_ERR(t))
+	t = btf_find_func_proto(funcname, &btf);
+	if (!t)
 		return (const struct btf_param *)t;
 
-	*nr = btf_type_vlen(t);
-	param = (const struct btf_param *)(t + 1);
+	param = btf_get_func_param(t, nr);
+	if (IS_ERR_OR_NULL(param))
+		goto err;
 
 	/* Hide the first 'data' argument of tracepoint */
 	if (tracepoint) {
@@ -421,6 +390,7 @@ static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr
 		return param;
 	}
 
+err:
 	btf_put(btf);
 	return NULL;
 }
@@ -496,8 +466,8 @@ static const struct fetch_type *parse_btf_retval_type(
 
 	if (ctx->funcname) {
 		/* Do not use ctx->btf, because it must be used with ctx->param */
-		t = find_btf_func_proto(ctx->funcname, &btf);
-		if (!IS_ERR(t)) {
+		t = btf_find_func_proto(ctx->funcname, &btf);
+		if (t) {
 			typestr = type_from_btf_id(btf, t->type);
 			btf_put(btf);
 		}
@@ -512,8 +482,8 @@ static bool is_btf_retval_void(const char *funcname)
 	struct btf *btf;
 	bool ret;
 
-	t = find_btf_func_proto(funcname, &btf);
-	if (IS_ERR(t))
+	t = btf_find_func_proto(funcname, &btf);
+	if (!t)
 		return false;
 
 	ret = (t->type == 0);