linux-kernel - Re: [PATCH 0/2] add new notifier function ,take2

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Message-Id: <20071018000651.35b26e42.akpm@linux-foundation.org>
Date:	Thu, 18 Oct 2007 00:06:51 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Takenori Nagano <t-nagano@...jp.nec.com>
Cc:	linux-kernel@...r.kernel.org, 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>,
	kdb@....sgi.com
Subject: Re: [PATCH 0/2] add new notifier function ,take2

On Thu, 18 Oct 2007 15:45:08 +0900 Takenori Nagano <t-nagano@...jp.nec.com> wrote:

> Hi,
> 
> A big thanks to everybody who read and replied to first version. I have tried to
> incorporate reviewer's comments and suggestions.
> 
> changelog take1 -> take2
> 
> - Rebased 2.6.23
> - comment updated
> - renamed the notifiner name "tunable_notifier" to "tunable_atomic_notifier"
> - fixed typo
> 
> 
> 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 debugfs.
> 
> Thanks,
> 
> Example)
> 
> # cd /sys/kernel/debug/
> # ls
> kprobes  pktcdvd
> # insmod ipmi_msghandler.ko
> # ls
> kprobes  panic_notifier_list  pktcdvd
> # cd panic_notifier_list/
> # ls
> ipmi_msghandler
> # insmod ipmi_watchdog.ko
> # ls
> ipmi_msghandler  ipmi_wdog
> # cat ipmi_msghandler/priority
> 200
> # cat ipmi_wdog/priority
> 150
> #
> Kernel panic - not syncing: panic
> ipmi_msghandler : notifier calls panic_event().
> ipmi_watchdog : notifier calls wdog_panic_handler().
> 
> .....(reboot)
> 
> # cat ipmi_msghandler/priority
> 200
> # cat ipmi_wdog/priority
> 150
> # echo 300 > ipmi_wdog/priority
> #
> Kernel panic - not syncing: panic
> ipmi_watchdog : notifier calls wdog_panic_handler().
> ipmi_msghandler : notifier calls panic_event().

I can sort-of see what this is doing.  Runtime-definable management of
which notifier functions will be called on a panic?  Or maybe I
misunderstood.

But even if I did understand, I don't understand why Linux needs this
feature - what are the use cases, what is the value to our users?

Can you please flesh that information out a bit more?

The patches are somewhat wordwrapped - please check your email client
configuration, thanks.
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