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

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Message-ID: <wzbyv7fvzgpf4ta775of6k4ozypnfe6szysvnz4odd3363ipsp@2v3h5w77cr7a>
Date: Wed, 4 Jun 2025 11:07:41 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Michal Luczaj <mhal@...x.co>
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 Wed, May 28, 2025 at 10:44:42PM +0200, Michal Luczaj wrote:
>Return a bitmap of registered vsock transports. As guesstimated by grepping
>/proc/kallsyms (CONFIG_KALLSYMS=y) for known symbols of type `struct
>virtio_transport`.
>
>Suggested-by: Stefano Garzarella <sgarzare@...hat.com>
>Signed-off-by: Michal Luczaj <mhal@...x.co>
>---
> tools/testing/vsock/util.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++
> tools/testing/vsock/util.h | 12 ++++++++++
> 2 files changed, 72 insertions(+)
>
>diff --git a/tools/testing/vsock/util.c b/tools/testing/vsock/util.c
>index b7b3fb2221c1682ecde58cf12e2f0b0ded1cff39..74fb52f566148b16436251216dd9d9275f0ec95b 100644
>--- a/tools/testing/vsock/util.c
>+++ b/tools/testing/vsock/util.c
>@@ -7,6 +7,7 @@
>  * Author: Stefan Hajnoczi <stefanha@...hat.com>
>  */
>
>+#include <ctype.h>
> #include <errno.h>
> #include <stdio.h>
> #include <stdint.h>
>@@ -17,6 +18,7 @@
> #include <assert.h>
> #include <sys/epoll.h>
> #include <sys/mman.h>
>+#include <linux/kernel.h>
> #include <linux/sockios.h>
>
> #include "timeout.h"
>@@ -854,3 +856,61 @@ void enable_so_linger(int fd, int timeout)
> 		exit(EXIT_FAILURE);
> 	}
> }
>+
>+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?

>+	char buf[KALLSYMS_LINE_LEN];
>+	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 < ARRAY_SIZE(syms); ++i) {
>+			match = strstr(buf, syms[i]);
>+
>+			/* Match should be followed by '\t' or '\n'.
>+			 * See kallsyms.c:s_show().
>+			 */
>+			if (match && isspace(match[strlen(syms[i])])) {
>+				ret |= _BITUL(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;
>+}
>diff --git a/tools/testing/vsock/util.h b/tools/testing/vsock/util.h
>index 0afe7cbae12e5194172c639ccfbeb8b81f7c25ac..63953e32c3e18e1aa5c2addcf6f09f433660fa84 100644
>--- a/tools/testing/vsock/util.h
>+++ b/tools/testing/vsock/util.h
>@@ -3,8 +3,19 @@
> #define UTIL_H
>
> #include <sys/socket.h>
>+#include <linux/bitops.h>
> #include <linux/vm_sockets.h>
>
>+#define KALLSYMS_PATH		"/proc/kallsyms"
>+#define KALLSYMS_LINE_LEN	512

We don't need to expose them in util.h IMO, we can keep in util.c

>+
>+/* All known transports */
>+#define TRANSPORT_LOOPBACK	_BITUL(0)
>+#define TRANSPORT_VIRTIO	_BITUL(1)
>+#define TRANSPORT_VHOST		_BITUL(2)
>+#define TRANSPORT_VMCI		_BITUL(3)
>+#define TRANSPORT_HYPERV	_BITUL(4)
>+
> /* Tests can either run as the client or the server */
> enum test_mode {
> 	TEST_MODE_UNSET,
>@@ -82,4 +93,5 @@ 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 */
>
>-- 
>2.49.0
>