linux-kernel - Re: module: sysfs - add 'uevent' file to allow coldplug

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Message-ID: <BANLkTinL4r3RfNuA5x6=UK4DCSSJNeZw7w@mail.gmail.com>
Date:	Wed, 22 Jun 2011 00:47:55 +0200
From:	Kay Sievers <kay.sievers@...y.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Greg KH <greg@...ah.com>
Subject: Re: module: sysfs - add 'uevent' file to allow coldplug

On Tue, Jun 21, 2011 at 03:53, Rusty Russell <rusty@...tcorp.com.au> wrote:
> On Mon, 20 Jun 2011 13:20:00 +0200, Kay Sievers <kay.sievers@...y.org> wrote:
>> On Mon, Jun 20, 2011 at 01:23, Rusty Russell <rusty@...tcorp.com.au> wrote:
>> > On Sun, 19 Jun 2011 00:00:29 +0200, Kay Sievers <kay.sievers@...y.org> wrote:
>> >> From: Kay Sievers <kay.sievers@...y.org>
>> >> Subject: module: sysfs - add 'uevent' file to allow built-in coldplug
>> >>
>> >> Userspace wants to manage module parameters with udev rules.
>> >> This currently only works for loaded modules, but not for
>> >> built-in ones.
>> >
>> > I'm confused.  What does "manage" mean here?
>>
>> Hook system management into module-load events, which might include
>> changing module parameters in /sys/module/*/parameters/*, or at
>> bootup/coldplug run it for built-in modules.
>>
>> We do the same to set properties for buses, drivers or devices when they appear.
>
> Sorry, that's another vague answer :(
>
> udev already knows about module load

Not for built-ins.

> and the parameters are created at
> that point; they are not *changed*.

The can be changed, and sometimes they need.

> What, *exactly* will this enable?  Don't use the word "hook" or
> "management": both vague terms which assume I know what you're talking
> about.  I don't.

Just used these words because it's absolutely generic infrastructure
we use already everywhere in /sys. :) Just run a: find /sys -name
uevent


> Show me exactly what udev will now be able to do that it can't do now,
> and how it will be used.  Preferably with examples.  Assume (correctly)
> that I have only a vague idea what udev does.

Set the polling interval of a always-built-in module parameter:

SUBSYSTEM=="module", KERNEL=="block",
ATTR{parameters/events_dfl_poll_msecs}="2000"

http://git.kernel.org/?p=linux/hotplug/udev.git;a=commitdiff;h=c5a41da94916815ac14d950a0547bffc4411f7af

Kay
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