Re: [PATCH net-next] tools: ynl: make ynl.c more c++ friendly

On 08/14, Jakub Kicinski wrote:

On Thu, 14 Aug 2025 09:44:13 -0700 Stanislav Fomichev wrote:

quoted

Compiling ynl.c in a C++ code base requires invoking C compiler and
using extern "C" for the headers. To make it easier, we can add
small changes to the ynl.c file to make it palatable to the native
C++ compiler. The changes are:
- avoid using void* pointer arithmetic, use char* instead
- avoid implicit void* type casts, add c-style explicit casts
- avoid implicit int->enum type casts, add c-style explicit casts
- avoid anonymous structs (for type casts)
- namespacify cpp version, this should let us compile both ynl.c
  as c and ynl.c as cpp in the same binary (YNL_CPP can be used
  to enable/disable namespacing)

Also add test_cpp rule to make sure ynl.c won't break C++ in the future.

As I mentioned in person, ynl-cpp is a separate thing, and you'd all
benefit from making it more C++ than going the other way and massaging
YNL C.

With that said, commenting below on the few that I think would be okay.

Ok, and the rest (typecasts mostly and the namespace) - you're not supper
happy about? I can drop that test_cpp if that helps :-)

quoted

@@ -224,7 +228,7 @@ static inline void *ynl_attr_data_end(const struct nlattr *attr)
 
 #define ynl_attr_for_each_payload(start, len, attr)			\
 	for ((attr) = ynl_attr_first(start, len, 0); attr;		\
-	     (attr) = ynl_attr_next(start + len, attr))
+	     (attr) = ynl_attr_next((char *)start + len, attr))

okay

quoted

@@ -149,7 +153,7 @@ ynl_err_walk(struct ynl_sock *ys, void *start, void *end, unsigned int off,
 		return n;
 	}
 
-	data_len = end - start;
+	data_len = (char *)end - (char *)start;

can we make the arguments char * instead of the casts?

Let me try. That might require to char-ify helpers like ynl_nlmsg_data_offset
and ynl_nlmsg_end_addr.