Thread (14 messages) 14 messages, 2 authors, 2025-06-11

Re: [PATCH RFC net-next v2 2/3] vsock/test: Introduce get_transports()

From: Michal Luczaj <hidden>
Date: 2025-06-11 20:35:38
Also in: lkml, virtualization

On 6/11/25 16:20, Stefano Garzarella wrote:
On Fri, Jun 06, 2025 at 09:51:29AM +0200, Michal Luczaj wrote:
quoted
On 6/5/25 12:46, Stefano Garzarella wrote:
quoted
On Wed, Jun 04, 2025 at 09:10:19PM +0200, Michal Luczaj wrote:
quoted
On 6/4/25 11:07, Stefano Garzarella wrote:
quoted
On Wed, May 28, 2025 at 10:44:42PM +0200, Michal Luczaj wrote:
quoted
+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.
quoted
quoted
	_(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/ (local)

Thanks,
Michal
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