linux-kernel - Re: loading ipmi_watchdog causes tons of other watchdog modules to be loaded

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Message-Id: <200810092218.29000.a.miskiewicz@gmail.com>
Date:	Thu, 9 Oct 2008 22:18:28 +0200
From:	Arkadiusz Miskiewicz <a.miskiewicz@...il.com>
To:	"Kay Sievers" <kay.sievers@...y.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: loading ipmi_watchdog causes tons of other watchdog modules to be loaded

On Thursday 09 of October 2008, Kay Sievers wrote:
> On Thu, Oct 9, 2008 at 9:02 PM, Arkadiusz Miskiewicz
>
> <a.miskiewicz@...il.com> wrote:
> > On Thursday 09 October 2008, Kay Sievers wrote:
> >> On Thu, Oct 9, 2008 at 7:22 PM, Arkadiusz Miskiewicz
> >>
> >> > ... but that ipmi_watchdog is the correct driver that handles
> >> > /dev/watchdog, so this shouldn't be happening, correct?
> >>
> >> While the driver you expect to work is loaded, what does:
> >>   ls -l /dev/watchdog
> >> print?
> >>
> >> If the devno of this node is 10:130, what does:
> >>   find /sys/class /sys/devices/ -name dev | xargs grep 10:130
> >> print?
> >
> > # ls -l /dev/watchdog
> > crw------- 1 root root 10, 130 sie  8 17:00 /dev/watchdog
> > # find /sys/class /sys/devices/ -name dev | xargs grep 10:130
> > /sys/class/misc/watchdog/dev:10:130
>
> Ok, so you actually have a driver bound to that device number, and it
> should not trigger the usual module autoloading mechanism.
>
> What does:
>   ls -l /sys/class/misc/watchdog/

# ls -l /sys/class/misc/watchdog/
razem 0
-r--r--r-- 1 root root 4096 paź  9 22:02 dev
drwxr-xr-x 2 root root    0 paź  9 22:02 power
lrwxrwxrwx 1 root root    0 paź  9 22:22 subsystem -> ../../misc
-rw-r--r-- 1 root root 4096 paź  9 22:02 uevent


> and
>   ls -l /sys/class/misc/watchdog/device/
> print?

# LC_ALL=C ls -l /sys/class/misc/watchdog/device/
ls: cannot access /sys/class/misc/watchdog/device/: No such file or directory


> Does the /sys/class/misc/watchdog/ directory exist, before you load
> the module you expect to be the driver behind /dev/watchdog?

It doesn't exist before. modprobe ipmi_watchdog, 
then /sys/class/misc/watchdog/ becomes available.

> To clarify, the other modules get loaded, after you loaded but module,
> the above /sys/class/misc/watchdog/ directory exists, and only if you
> read from the device, all the other modules get loaded?

Exactly.  I load ipmi_watchdog, /sys/class/misc/watchdog/ becomes available 
(no /sys/class/misc/watchdog/device/ though), then cat /dev/watchdog and this 
causes that other watchdog modules are loaded.

> Kay

-- 
Arkadiusz Miśkiewicz        PLD/Linux Team
arekm / maven.pl            http://ftp.pld-linux.org/
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