vsock/test: Introduce get_transports()

Return a bitmap of registered vsock transports. As guesstimated by grepping
/proc/kallsyms (CONFIG_KALLSYMS=y) for known symbols of type `struct
vsock_transport`, or `struct virtio_transport` in case the vsock_transport
is embedded within.

Note that the way `enum transport` and `transport_ksyms[]` are defined
triggers checkpatch.pl:

util.h:11: ERROR: Macros with complex values should be enclosed in parentheses
util.h:20: ERROR: Macros with complex values should be enclosed in parentheses
util.h:20: WARNING: Argument 'symbol' is not used in function-like macro
util.h:28: WARNING: Argument 'name' is not used in function-like macro

While commit 15d4734c7a ("checkpatch: qualify do-while-0 advice")
suggests it is known that the ERRORs heuristics are insufficient, I can not
find many other places where preprocessor is used in this
checkpatch-unhappy fashion. Notable exception being bcachefs, e.g.
fs/bcachefs/alloc_background_format.h. WARNINGs regarding unused macro
arguments seem more common, e.g. __ASM_SEL in arch/x86/include/asm/asm.h.

In other words, this might be unnecessarily complex. The same can be
achieved by just telling human to keep the order:

enum transport {
	TRANSPORT_LOOPBACK = BIT(0),
	TRANSPORT_VIRTIO = BIT(1),
	TRANSPORT_VHOST = BIT(2),
	TRANSPORT_VMCI = BIT(3),
	TRANSPORT_HYPERV = BIT(4),
	TRANSPORT_NUM = 5,
};

 #define KSYM_ENTRY(sym) "d " sym "_transport"

/* Keep `enum transport` order */
static const char * const transport_ksyms[] = {
	KSYM_ENTRY("loopback"),
	KSYM_ENTRY("virtio"),
	KSYM_ENTRY("vhost"),
	KSYM_ENTRY("vmci"),
	KSYM_ENTRY("vhs"),
};

Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Tested-by: Luigi Leonardi <leonardi@redhat.com>
Reviewed-by: Luigi Leonardi <leonardi@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://patch.msgid.link/20250611-vsock-test-inc-cov-v3-2-5834060d9c20@rbox.co
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/vsock/util.c

@@ -7,6 +7,7 @@
  * Author: Stefan Hajnoczi <stefanha@redhat.com>
  */
 
+#include <ctype.h>
 #include <errno.h>
 #include <stdio.h>
 #include <stdint.h>
@@ -23,6 +24,9 @@
 #include "control.h"
 #include "util.h"
 
+#define KALLSYMS_PATH		"/proc/kallsyms"
+#define KALLSYMS_LINE_LEN	512
+
 /* Install signal handlers */
 void init_signals(void)
 {
@@ -854,3 +858,55 @@ void enable_so_linger(int fd, int timeout)
 		exit(EXIT_FAILURE);
 	}
 }
+
+static int __get_transports(void)
+{
+	char buf[KALLSYMS_LINE_LEN];
+	const char *ksym;
+	int ret = 0;
+	FILE *f;
+
+	f = fopen(KALLSYMS_PATH, "r");
+	if (!f) {
+		perror("Can't open " KALLSYMS_PATH);
+		exit(EXIT_FAILURE);
+	}
+
+	while (fgets(buf, sizeof(buf), f)) {
+		char *match;
+		int i;
+
+		assert(buf[strlen(buf) - 1] == '\n');
+
+		for (i = 0; i < TRANSPORT_NUM; ++i) {
+			if (ret & BIT(i))
+				continue;
+
+			/* Match should be followed by '\t' or '\n'.
+			 * See kallsyms.c:s_show().
+			 */
+			ksym = transport_ksyms[i];
+			match = strstr(buf, ksym);
+			if (match && isspace(match[strlen(ksym)])) {
+				ret |= BIT(i);
+				break;
+			}
+		}
+	}
+
+	fclose(f);
+	return ret;
+}
+
+/* Return integer with TRANSPORT_* bit set for every (known) registered vsock
+ * transport.
+ */
+int get_transports(void)
+{
+	static int tr = -1;
+
+	if (tr == -1)
+		tr = __get_transports();
+
+	return tr;
+}

tools/testing/vsock/util.h

@@ -3,8 +3,36 @@
 #define UTIL_H
 
 #include <sys/socket.h>
+#include <linux/bitops.h>
+#include <linux/kernel.h>
 #include <linux/vm_sockets.h>
 
+/* All known vsock transports, see callers of vsock_core_register() */
+#define KNOWN_TRANSPORTS(x)		\
+	x(LOOPBACK, "loopback")		\
+	x(VIRTIO, "virtio")		\
+	x(VHOST, "vhost")		\
+	x(VMCI, "vmci")			\
+	x(HYPERV, "hvs")
+
+enum transport {
+	TRANSPORT_COUNTER_BASE = __COUNTER__ + 1,
+	#define x(name, symbol)		\
+		TRANSPORT_##name = BIT(__COUNTER__ - TRANSPORT_COUNTER_BASE),
+	KNOWN_TRANSPORTS(x)
+	TRANSPORT_NUM = __COUNTER__ - TRANSPORT_COUNTER_BASE,
+	#undef x
+};
+
+static const char * const transport_ksyms[] = {
+	#define x(name, symbol) "d " symbol "_transport",
+	KNOWN_TRANSPORTS(x)
+	#undef x
+};
+
+static_assert(ARRAY_SIZE(transport_ksyms) == TRANSPORT_NUM);
+static_assert(BITS_PER_TYPE(int) >= TRANSPORT_NUM);
+
 /* Tests can either run as the client or the server */
 enum test_mode {
 	TEST_MODE_UNSET,
@@ -82,4 +110,5 @@ void setsockopt_timeval_check(int fd, int level, int optname,
 			      struct timeval val, char const *errmsg);
 void enable_so_zerocopy_check(int fd);
 void enable_so_linger(int fd, int timeout);
+int get_transports(void);
 #endif /* UTIL_H */