linux-kernel - Re: What is listed in /sys/module?

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Message-ID: <878v2xmgmw.fsf@rustcorp.com.au>
Date:	Thu, 30 May 2013 10:24:31 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Jean Delvare <khali@...ux-fr.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: What is listed in /sys/module?

Jean Delvare <khali@...ux-fr.org> writes:
> Hi Greg, Rusty,
>
> I have a question related to /sys/module and can't seem to find the
> answer by myself so I hope you can explain.
>
> I noticed that /sys/module contains more than /proc/modules. At first I
> thought that any potentially modular piece of code would show up
> in /sys/module, so /sys/module would include both actual modules and
> "built-in modules".
>
> However I then noticed that some built-in modules do _not_ show up
> in /sys/module. For example, I have USB and I2C core support built into
> my 3.9.4 kernel, /sys/module/usbcore exists but /sys/module/i2c_core
> does not. CONFIG_SENSORS_W83795=y did not give me /sys/module/w83795
> either.

Yes.  /sys/module entries are created for builtin "modules" with
parameters.  This is because, the module names are discovered by
scouring the parameters: see param_sysfs_builtin().

Two things to note about builtin modules:

1) There is nothing other than parameters in /sys/module/, except a
   uevent which is used for managing the parameters.  So, without
   parameters, it would be an empty directory.

2) We actually do generate a list of builtin modules these days, called
   modules.builtin.  So we could generate sysfs dirs from this.

If you want to make it consistent, I look forward to your patch!

Cheers,
Rusty.
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