[PATCH nft 3/5] datatype: don't clone datatype in set_datatype_alloc() if byteorder already matches

[Thomas Haller <thaller@redhat.com>]

"struct datatype" instances are treated immutable and not changed after
creation.  set_datatype_alloc() returns a const pointer, indicating that
the caller must not modify the instance anymore. In particular it must
not, because for non-integer types we just return a reference to the
(already immutable) orig_dtype.

If the byteorder that we are about to set is already as-requested, there
is no need to clone the instance either. Just return a reference to
orig_dtype() too.

Also drop the same optimization from key_fix_dtype_byteorder().

Signed-off-by: Thomas Haller <thaller@redhat.com>
---
 src/datatype.c |  6 +++++-
 src/evaluate.c | 19 +++++++------------
 2 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/src/datatype.c b/src/datatype.c
index 1c557a06c751..6a35c6a76028 100644
--- a/src/datatype.c
+++ b/src/datatype.c
@@ -1321,9 +1321,13 @@ const struct datatype *set_datatype_alloc(const struct datatype *orig_dtype,
 	if (orig_dtype != &integer_type)
 		return datatype_get(orig_dtype);
 
+	if (orig_dtype->byteorder == byteorder) {
+		/* The (immutable) type instance is already as requested. */
+		return datatype_get(orig_dtype);
+	}
+
 	dtype = datatype_clone(orig_dtype);
 	dtype->byteorder = byteorder;
-
 	return dtype;
 }
 
diff --git a/src/evaluate.c b/src/evaluate.c
index c699a9bc7b86..e84895bf1610 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -74,17 +74,8 @@ static int __fmtstring(3, 4) set_error(struct eval_ctx *ctx,
 	return -1;
 }
 
-static void key_fix_dtype_byteorder(struct expr *key)
-{
-	const struct datatype *dtype = key->dtype;
-
-	if (dtype->byteorder == key->byteorder)
-		return;
-
-	__datatype_set(key, set_datatype_alloc(dtype, key->byteorder));
-}
-
 static int set_evaluate(struct eval_ctx *ctx, struct set *set);
+
 static struct expr *implicit_set_declaration(struct eval_ctx *ctx,
 					     const char *name,
 					     struct expr *key,
@@ -95,8 +86,12 @@ static struct expr *implicit_set_declaration(struct eval_ctx *ctx,
 	struct set *set;
 	struct handle h;
 
-	if (set_is_datamap(expr->set_flags))
-		key_fix_dtype_byteorder(key);
+	if (set_is_datamap(expr->set_flags)) {
+		const struct datatype *dtype;
+
+		dtype = set_datatype_alloc(key->dtype, key->byteorder);
+		__datatype_set(key, dtype);
+	}
 
 	set = set_alloc(&expr->location);
 	set->flags	= NFT_SET_ANONYMOUS | expr->set_flags;
-- 
2.41.0