[PATCH bpf-next v2 02/13] bpf: Add helper btf_find_dynptr()

[Hou Tao <houtao@huaweicloud.com>]

From: Hou Tao <houtao1@huawei.com>

Add helper btf_find_dynptr() to check whether or not the passed btf type
is bpf_dynptr. It can be extend to find an embedded dynptr in passed btf
type if needed later.

It will be used by bpf map (e.g. qp-trie) with bpf_dynptr key.

Signed-off-by: Hou Tao <houtao1@huawei.com>
---
 include/linux/btf.h |  1 +
 kernel/bpf/btf.c    | 13 +++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/include/linux/btf.h b/include/linux/btf.h
index f9aababc5d78..5bf508c2bad2 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -165,6 +165,7 @@ int btf_find_spin_lock(const struct btf *btf, const struct btf_type *t);
 int btf_find_timer(const struct btf *btf, const struct btf_type *t);
 struct bpf_map_value_off *btf_parse_kptrs(const struct btf *btf,
 					  const struct btf_type *t);
+int btf_find_dynptr(const struct btf *btf, const struct btf_type *t);
 bool btf_type_is_void(const struct btf_type *t);
 s32 btf_find_by_name_kind(const struct btf *btf, const char *name, u8 kind);
 const struct btf_type *btf_type_skip_modifiers(const struct btf *btf,
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index a44ad4b347ff..fefbe84c6998 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3522,6 +3522,19 @@ struct bpf_map_value_off *btf_parse_kptrs(const struct btf *btf,
 	return ERR_PTR(ret);
 }
 
+/* Now only allow to use 'struct bpf_dynptr' as map key.
+ * Map key with embedded bpf_dynptr is not allowed.
+ */
+int btf_find_dynptr(const struct btf *btf, const struct btf_type *t)
+{
+	/* Only allow struct type */
+	if (__btf_type_is_struct(t) && t->size == sizeof(struct bpf_dynptr) &&
+	    !strcmp("bpf_dynptr", __btf_name_by_offset(btf, t->name_off)))
+		return 0;
+
+	return -EINVAL;
+}
+
 static void __btf_struct_show(const struct btf *btf, const struct btf_type *t,
 			      u32 type_id, void *data, u8 bits_offset,
 			      struct btf_show *show)
-- 
2.29.2