linux-kernel - Re: Class device namespaces

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Message-ID: <437908170904291428k445fc8fdy9b3bb4e78ee91018@mail.gmail.com>
Date:	Wed, 29 Apr 2009 16:28:35 -0500
From:	Michael Brown <mebrown@...haels-house.net>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	Doug Warzecha <Douglas_Warzecha@...l.com>,
	Jean Delvare <khali@...ux-fr.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	linux-kernel@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Matt Domsch <Matt_Domsch@...l.com>
Subject: Re: Class device namespaces

On Wed, Apr 29, 2009 at 2:10 PM, Kay Sievers <kay.sievers@...y.org> wrote:
> Udev runs exactly at the time you create the device, and is not
> unlikely faster than your polling, at least not predictable slower.
> And it will cancel all requests which can not be fulfilled by udev
> itself.
>
> I strongly recommend switching to a different solution, you can not
> use the firmware_class interface on any udev system, the interface is
> already taken, and it's a single-user interface the way it is
> implemented today. That it seems to work for you, is pure luck, I
> guess. :)

Is there a safe/easy way to tell udev that we will handle a particular
request? I cant say that I've ever seen any problems due to udev
cancelling a firmware request.  In fact, if I manually trigger a
request using "echo" from the cmdline, I dont see udev take any action
with the dell_rbu device. eg (Fedora 10, udev-127-5.fc10):

# find /sys -name dell_rbu
/sys/devices/platform/dell_rbu
/sys/bus/platform/devices/dell_rbu
/sys/module/dell_rbu
[root@duo dell_rbu]# echo "init" > /sys/devices/platform/dell_rbu/image_type
[root@duo dell_rbu]# find /sys -name dell_rbu
/sys/devices/platform/dell_rbu
/sys/devices/platform/dell_rbu/firmware/dell_rbu
/sys/bus/platform/devices/dell_rbu
/sys/class/firmware/dell_rbu
/sys/module/dell_rbu
[root@duo dell_rbu]# ll /sys/class/firmware/dell_rbu/
total 0
-rw-r--r-- 1 root root    0 2009-04-29 16:25 data
lrwxrwxrwx 1 root root    0 2009-04-29 16:25 device -> ../../../dell_rbu
-rw-r--r-- 1 root root 4096 2009-04-29 16:25 loading
drwxr-xr-x 2 root root    0 2009-04-29 16:25 power
lrwxrwxrwx 1 root root    0 2009-04-29 16:25 subsystem ->
../../../../../class/firmware
-rw-r--r-- 1 root root 4096 2009-04-29 16:25 uevent
[root@duo dell_rbu]#
[root@duo dell_rbu]# echo 0 > /sys/class/firmware/dell_rbu/loading
[root@duo dell_rbu]#
[root@duo dell_rbu]# find /sys -name dell_rbu
/sys/devices/platform/dell_rbu
/sys/bus/platform/devices/dell_rbu
/sys/module/dell_rbu

I dont see any of the behaviour that you have talked about. If I let
it sit there for hours, it will stay at that state. It only closes up
the request_firmware() request when I echo 0 > loading.

At this point, we have had this interface in the upstream kernel.org
kernel since 2.6.14 and have a pretty huge legacy codebase that relies
on this behaviour. We need to make sure that the current behaviour
remains.

--
Michael
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