On Sun, Sep 29, 2024 at 6:56 PM Michael S. Tsirkin [off-list ref] wrote:

On Thu, Sep 26, 2024 at 06:16:40PM +0200, Alexander Mikhalitsyn wrote:

quoted

Add an explicit MODULE_VERSION("0.0.1") specification
for a vhost_vsock module. It is useful because it allows
userspace to check if vhost_vsock is there when it is
configured as a built-in.

Without this change, there is no /sys/module/vhost_vsock directory.

With this change:
$ ls -la /sys/module/vhost_vsock/
total 0
drwxr-xr-x   2 root root    0 Sep 26 15:59 .
drwxr-xr-x 100 root root    0 Sep 26 15:59 ..
--w-------   1 root root 4096 Sep 26 15:59 uevent
-r--r--r--   1 root root 4096 Sep 26 15:59 version

Signed-off-by: Alexander Mikhalitsyn <redacted>

Dear Michael,

Why not check that the misc device is registered?

It is possible to read /proc/misc and check if "241 vhost-vsock" is
there, but it means that userspace
needs to have a specific logic for vsock. At the same time, it's quite
convenient to do something like:
    if [ ! -d /sys/modules/vhost_vsock ]; then
        modprobe vhost_vsock
    fi

I'd rather not add a new UAPI until actually necessary.

I don't insist. I decided to send this patch because, while I was
debugging a non-related kernel issue
on my local dev environment I accidentally discovered that LXD
(containers and VM manager)
fails to run VMs because it fails to load the vhost_vsock module (but
it was built-in in my debug kernel
and the module file didn't exist). Then I discovered that before
trying to load a module we
check if /sys/module/<module name> exists. And found that, for some
reason /sys/module/vhost_vsock
does not exist when vhost_vsock is configured as a built-in, and
/sys/module/vhost_vsock *does* exist when
vhost_vsock is loaded as a module. It looks like an inconsistency and
I also checked that other modules in
drivers/vhost have MODULE_VERSION specified and version is 0.0.1. I
thought that this change looks legitimate
and convenient for userspace consumers.

Kind regards,
Alex

quoted

---
 drivers/vhost/vsock.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 802153e23073..287ea8e480b5 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c

@@ -956,6 +956,7 @@ static void __exit vhost_vsock_exit(void)

 module_init(vhost_vsock_init);
 module_exit(vhost_vsock_exit);
+MODULE_VERSION("0.0.1");
 MODULE_LICENSE("GPL v2");
 MODULE_AUTHOR("Asias He");
 MODULE_DESCRIPTION("vhost transport for vsock ");
--

2.34.1