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

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Message-ID: <9f1f41eb-e23e-48c9-a6bc-db9d34dbae5e@rbox.co>
Date: Wed, 11 Jun 2025 22:35:19 +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 6/11/25 16:20, Stefano Garzarella wrote:
> On Fri, Jun 06, 2025 at 09:51:29AM +0200, Michal Luczaj wrote:
>> 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).
> 
> It's just test, so I think it's fine to ignore, but please exaplain it 
> in the commit description with also references to other ERRORs/WARNINGs 
> like you did here. Let's see what net maintainers think.

Sure, I've added a note. I've also switched the magic macro name '_' to
'x', this seems to be more common.

https://lore.kernel.org/netdev/20250611-vsock-test-inc-cov-v3-0-5834060d9c20@rbox.co/

Thanks,
Michal