linux-kernel - Re: [PATCH RFC net-next v2 2/3] vsock/test: Introduce get

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Message-ID: <adae2539-2a48-45c3-a340-e9ab3776941f@rbox.co>
Date: Fri, 6 Jun 2025 09:51:29 +0200
From: Michal Luczaj <mhal@...x.co>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: virtualization@...ts.linux.dev, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC net-next v2 2/3] vsock/test: Introduce
 get_transports()

On 6/5/25 12:46, Stefano Garzarella wrote:
> On Wed, Jun 04, 2025 at 09:10:19PM +0200, Michal Luczaj wrote:
>> On 6/4/25 11:07, Stefano Garzarella wrote:
>>> On Wed, May 28, 2025 at 10:44:42PM +0200, Michal Luczaj wrote:
>>>> +static int __get_transports(void)
>>>> +{
>>>> +	/* Order must match transports defined in util.h.
>>>> +	 * man nm: "d" The symbol is in the initialized data section.
>>>> +	 */
>>>> +	const char * const syms[] = {
>>>> +		"d loopback_transport",
>>>> +		"d virtio_transport",
>>>> +		"d vhost_transport",
>>>> +		"d vmci_transport",
>>>> +		"d hvs_transport",
>>>> +	};
>>>
>>> I would move this array (or a macro that define it), near the transport
>>> defined in util.h, so they are near and we can easily update/review
>>> changes.
>>>
>>> BTW what about adding static asserts to check we are aligned?
>>
>> Something like
>>
>> #define KNOWN_TRANSPORTS	\
> 
> What about KNOWN_TRANSPORTS(_) ?

Ah, yeah.

>> 	_(LOOPBACK, "loopback")	\
>> 	_(VIRTIO, "virtio")	\
>> 	_(VHOST, "vhost")	\
>> 	_(VMCI, "vmci")		\
>> 	_(HYPERV, "hvs")
>>
>> enum transport {
>> 	TRANSPORT_COUNTER_BASE = __COUNTER__ + 1,
>> 	#define _(name, symbol)	\
>> 		TRANSPORT_##name = _BITUL(__COUNTER__ - TRANSPORT_COUNTER_BASE),
>> 	KNOWN_TRANSPORTS
>> 	TRANSPORT_NUM = __COUNTER__ - TRANSPORT_COUNTER_BASE,
>> 	#undef _
>> };
>>
>> static char * const transport_ksyms[] = {
>> 	#define _(name, symbol) "d " symbol "_transport",
>> 	KNOWN_TRANSPORTS
>> 	#undef _
>> };
>>
>> static_assert(ARRAY_SIZE(transport_ksyms) == TRANSPORT_NUM);
>>
>> ?
> 
> Yep, this is even better, thanks :-)

Although checkpatch complains:

ERROR: Macros with complex values should be enclosed in parentheses
#105: FILE: tools/testing/vsock/util.h:11:
+#define KNOWN_TRANSPORTS(_)	\
+	_(LOOPBACK, "loopback")	\
+	_(VIRTIO, "virtio")	\
+	_(VHOST, "vhost")	\
+	_(VMCI, "vmci")		\
+	_(HYPERV, "hvs")

BUT SEE:

   do {} while (0) advice is over-stated in a few situations:

   The more obvious case is macros, like MODULE_PARM_DESC, invoked at
   file-scope, where C disallows code (it must be in functions).  See
   $exceptions if you have one to add by name.

   More troublesome is declarative macros used at top of new scope,
   like DECLARE_PER_CPU.  These might just compile with a do-while-0
   wrapper, but would be incorrect.  Most of these are handled by
   detecting struct,union,etc declaration primitives in $exceptions.

   Theres also macros called inside an if (block), which "return" an
   expression.  These cannot do-while, and need a ({}) wrapper.

   Enjoy this qualification while we work to improve our heuristics.

ERROR: Macros with complex values should be enclosed in parentheses
#114: FILE: tools/testing/vsock/util.h:20:
+	#define _(name, symbol)	\
+		TRANSPORT_##name = BIT(__COUNTER__ - TRANSPORT_COUNTER_BASE),

WARNING: Argument 'symbol' is not used in function-like macro
#114: FILE: tools/testing/vsock/util.h:20:
+	#define _(name, symbol)	\
+		TRANSPORT_##name = BIT(__COUNTER__ - TRANSPORT_COUNTER_BASE),

WARNING: Argument 'name' is not used in function-like macro
#122: FILE: tools/testing/vsock/util.h:28:
+	#define _(name, symbol) "d " symbol "_transport",

Is it ok to ignore this? FWIW, I see the same ERRORs due to similarly used
preprocessor directives in fs/bcachefs/alloc_background_format.h, and the
same WARNINGs about unused macro arguments in arch/x86/include/asm/asm.h
(e.g. __ASM_SEL).