[PATCH bpf-next 02/16] bpf: Add two helpers to facilitate the btf parsing of bpf_dynptr

[Hou Tao <houtao@xxxxxxxxxxxxxxx>]

From: Hou Tao <houtao1@xxxxxxxxxx>

Add helper btf_type_is_dynptr() to check whether or not the btf_type is
a bpf_dynptr, and add helper btf_new_bpf_dynptr_record() to create an
btf record which only includes a bpf_dynptr. These two helpers will be
used when using bpf_dynptr as the map key directly.

Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
---
 include/linux/btf.h |  2 ++
 kernel/bpf/btf.c    | 42 +++++++++++++++++++++++++++++++++++++-----
 2 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/include/linux/btf.h b/include/linux/btf.h
index b8a583194c4a..ed89b83e8c19 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -222,8 +222,10 @@ bool btf_member_is_reg_int(const struct btf *btf, const struct btf_type *s,
 			   u32 expected_offset, u32 expected_size);
 struct btf_record *btf_parse_fields(const struct btf *btf, const struct btf_type *t,
 				    u32 field_mask, u32 value_size);
+struct btf_record *btf_new_bpf_dynptr_record(void);
 int btf_check_and_fixup_fields(const struct btf *btf, struct btf_record *rec);
 bool btf_type_is_void(const struct btf_type *t);
+bool btf_type_is_dynptr(const struct btf *btf, const struct btf_type *t);
 s32 btf_find_by_name_kind(const struct btf *btf, const char *name, u8 kind);
 s32 bpf_find_btf_id(const char *name, u32 kind, struct btf **btf_p);
 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 5254fc9c1b24..321356710924 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3923,6 +3923,16 @@ static int btf_field_cmp(const void *_a, const void *_b, const void *priv)
 	return 0;
 }
 
+static void btf_init_btf_record(struct btf_record *record)
+{
+	record->cnt = 0;
+	record->field_mask = 0;
+	record->spin_lock_off = -EINVAL;
+	record->timer_off = -EINVAL;
+	record->wq_off = -EINVAL;
+	record->refcount_off = -EINVAL;
+}
+
 struct btf_record *btf_parse_fields(const struct btf *btf, const struct btf_type *t,
 				    u32 field_mask, u32 value_size)
 {
@@ -3941,14 +3951,11 @@ struct btf_record *btf_parse_fields(const struct btf *btf, const struct btf_type
 	/* This needs to be kzalloc to zero out padding and unused fields, see
 	 * comment in btf_record_equal.
 	 */
-	rec = kzalloc(offsetof(struct btf_record, fields[cnt]), GFP_KERNEL | __GFP_NOWARN);
+	rec = kzalloc(struct_size(rec, fields, cnt), GFP_KERNEL | __GFP_NOWARN);
 	if (!rec)
 		return ERR_PTR(-ENOMEM);
 
-	rec->spin_lock_off = -EINVAL;
-	rec->timer_off = -EINVAL;
-	rec->wq_off = -EINVAL;
-	rec->refcount_off = -EINVAL;
+	btf_init_btf_record(rec);
 	for (i = 0; i < cnt; i++) {
 		field_type_size = btf_field_type_size(info_arr[i].type);
 		if (info_arr[i].off + field_type_size > value_size) {
@@ -4038,6 +4045,25 @@ struct btf_record *btf_parse_fields(const struct btf *btf, const struct btf_type
 	return ERR_PTR(ret);
 }
 
+struct btf_record *btf_new_bpf_dynptr_record(void)
+{
+	struct btf_record *record;
+
+	record = kzalloc(struct_size(record, fields, 1), GFP_KERNEL | __GFP_NOWARN);
+	if (!record)
+		return ERR_PTR(-ENOMEM);
+
+	btf_init_btf_record(record);
+
+	record->cnt = 1;
+	record->field_mask = BPF_DYNPTR;
+	record->fields[0].offset = 0;
+	record->fields[0].size = sizeof(struct bpf_dynptr);
+	record->fields[0].type = BPF_DYNPTR;
+
+	return record;
+}
+
 int btf_check_and_fixup_fields(const struct btf *btf, struct btf_record *rec)
 {
 	int i;
@@ -7276,6 +7302,12 @@ static bool btf_is_dynptr_ptr(const struct btf *btf, const struct btf_type *t)
 	return false;
 }
 
+bool btf_type_is_dynptr(const struct btf *btf, const struct btf_type *t)
+{
+	return __btf_type_is_struct(t) && t->size == sizeof(struct bpf_dynptr) &&
+	       !strcmp(__btf_name_by_offset(btf, t->name_off), "bpf_dynptr");
+}
+
 struct bpf_cand_cache {
 	const char *name;
 	u32 name_len;
-- 
2.44.0