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

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Message-ID: <87lib1j9ni.fsf@rustcorp.com.au>
Date:	Thu, 07 Feb 2013 10:08:09 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Cong Wang <xiyou.wangcong@...il.com>,
	Jesse Gross <jesse@...ira.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Jon Masters" <jcm@...hat.com>,
	"Lucas De Marchi" <lucas.demarchi@...fusion.mobi>
Subject: Re: No sysfs directory for openvswitch module when built-in

Ben Hutchings <bhutchings@...arflare.com> writes:
> On Mon, 2013-02-04 at 16:29 +1030, Rusty Russell wrote:
>> Cong Wang <xiyou.wangcong@...il.com> writes:
>> > 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.
>> 
>> We only know built-in "modules" exist if we see a parameter or version
>> which mention them.  Looking for /sys/module/openvswitch/ is almost as
>> flawed as looking in /proc/modules.
>> 
>> I hacked up something which lists KBUILD_MODNAME for every element in my
>> kernel which did EXPORT_KERNEL or module_init, and most of them can
>> never be modules, though any could have parameters.  Even if we changed
>> the build system so we could tell things which "could have been a
>> module", it's silly.
> [...]
>
> Isn't this information already provided by modules.builtin?

(CC's trimmed)

Thanks Ben, I learned something!  I hadn't spotted that tristate vars
get set to Y instead of y.  Subtle...

So we already have the infrastructure, and copy it into the module dir
(though logically it's a kernel property and belongs in /proc).
eg. lsmod doesn't list them, which is a bit weird, though modprobe
"succeeds".

A quick grep through my /etc shows 5 scripts using lsmod and 1 using
/sys/module to check for presence of modules.  Should the kernel pad
/proc/modules with entries for builtins?

Thoughts welcome...
Rusty.
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