linux-kernel - Re: [PATCH 0/2] add new notifier function ,take3

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Message-Id: <20080411210751.e4a468b2.akpm@linux-foundation.org>
Date:	Fri, 11 Apr 2008 21:07:51 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Takenori Nagano <t-nagano@...jp.nec.com>
Cc:	linux-kernel@...r.kernel.org, kdb@....sgi.com, vgoyal@...ibm.com,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	k-miyoshi@...jp.nec.com, kexec@...ts.infradead.org,
	Bernhard Walle <bwalle@...e.de>, Keith Owens <kaos@....com.au>,
	nickpiggin@...oo.com.au, Randy Dunlap <rdunlap@...otime.net>,
	greg@...ah.com
Subject: Re: [PATCH 0/2] add new notifier function ,take3

On Fri, 11 Apr 2008 16:53:47 +0900 Takenori Nagano <t-nagano@...jp.nec.com> wrote:

> Hi,
> 
> A big thanks to everybody who read and replied to previous version.
> 
> changelog take2 -> take3
> 
> - Rebased 2.6.25-rc8-mm1
> - comment updated
> - renamed the notifiner name "tunable_notifier" to "tunable_atomic_notifier"
> - fixed typo
> - move control files debugfs to /sys/kernel
> 
> These patches add new notifier function and implement it to panic_notifier_list.
> We used the hardcoded notifier chain so far, but it was not flexible. New
> notifier is very flexible, because user can change a list of order by control files.
> 
> Example)
> 
> # cd /sys/kernel/notifiers/
> # ls
> panic_notifier_list
> # cd panic_notifier_list/
> # ls
> ipmi_msghandler  ipmi_wdog
> # insmod notifier_test.ko
> # ls
> ipmi_msghandler  ipmi_wdog  notifier_test1  notifier_test2
> # cat */priority
> 200
> 150
> 500
> 1000
> Kernel panic - not syncing: Panic by panic_module.
> __tunable_atomic_notifier_call_chain enter
> notifier_test: notifier_test_panic2() is called.
> notifier_test: notifier_test_panic() is called.
> msg_handler:panic_event was called.
> ipmi_wdog:wdog_panic_handler was called.
> 
> .....(reboot)
> 
> # cd /sys/kernel/notifiers/panic_notifier_list/
> # ls
> ipmi_msghandler  ipmi_wdog  notifier_test1  notifier_test2
> # cat */priority
> 200
> 150
> 500
> 1000
> # echo 10000 > ipmi_msghandler/priority
> # echo 5000 > ipmi_wdog/priority
> # echo 3000 > notifier_test1/priority
> # echo 1500 > notifier_test2/priority
> # cat */priority
> 10000
> 5000
> 3000
> 1500
> Kernel panic - not syncing: Panic by panic_module.
> __tunable_atomic_notifier_call_chain enter
> msg_handler:panic_event was called.
> ipmi_wdog:wdog_panic_handler was called.
> notifier_test: notifier_test_panic() is called.
> notifier_test: notifier_test_panic2() is called.

OK.  But I don't see anywhere in here the most important piece of
information: why do we need this feature in Linux?

What are the use-cases?  What is the value?  etc.

Often I can guess (but I like the originator to remove the guesswork).  In
this case I'm stumped - I can't see any reason why anyone would want this.

Awaiting enlightenment ;)

Thanks.
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