linux-kernel - No sysfs directory for openvswitch module when built-in

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Date:	Tue, 29 Jan 2013 22:15:18 +0800
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	Rusty Russell <rusty@...tcorp.com.au>,
	Jesse Gross <jesse@...ira.com>,
	"David S. Miller" <davem@...emloft.net>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: No sysfs directory for openvswitch module when built-in

Hello, Rusty, Jesse,

I met an interesting problem when I compile openvswitch module as a
built-in (actually I compile ALL kernel modules as built-in), there is
no /sys/module/openvswitch/ directory created by the kernel in this
case.

What's worse, the user-space init script thinks openvswitch module is
not loaded by checking the exist of this directory, therefore refuses
to start.

After digging a little deeper, I found the cause of this problem is
actually that the core kernel doesn't create directory for any kernel
module without a module version or any module parameters when
built-in. Openvswitch is exactly such a module!!

I believe there is nothing wrong either in the user-space init script,
or in the openvswitch kernel module. So, the question why core kernel
doesn't create module directory for such modules?

>From the code:

static int __init param_sysfs_init(void)
{
        module_kset = kset_create_and_add("module", &module_uevent_ops, NULL);
        if (!module_kset) {
                printk(KERN_WARNING "%s (%d): error creating kset\n",
                        __FILE__, __LINE__);
                return -ENOMEM;
        }
        module_sysfs_initialized = 1;

        version_sysfs_builtin();
        param_sysfs_builtin();

        return 0;
}

it seems there is no way to get the name of the kernel module in such
case, the above searches module name either in parameter or in version
information. But I may miss something here...

We can certainly workaround this issue by providing a (dummy) version
in openvswitch module, but the more important question is can't we fix
this in core kernel? It is perfectly valid to provide a kernel module
without either a module version or any module parameter.

What do you think?

Thanks!
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