linux-kernel - Re: Loud "pop" coming from hard drive on reboot

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Date:	Wed, 18 Apr 2007 21:46:47 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	7eggert@....de, Chuck Ebbert <cebbert@...hat.com>,
	emisca <emisca.ml@...il.com>,
	Jan Engelhardt <jengelh@...ux01.gwdg.de>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-ide@...r.kernel.org, Adrian Bunk <bunk@...sta.de>,
	Andrew Morton <akpm@...l.org>
Subject: Re: Loud "pop" coming from hard drive on reboot

Alan Cox wrote:
>> Not that simple.  Most disks don't spin up on SYNCHRONIZE_CACHE if its 
>> cache is clean.  Sadly some disks actually spin up when it receives spin 
>> down command while spun down to immediately spin down again, so we would 
>> be fixing problem for some number of disks while breaking others.  :-(
> 
> Snoop the last command sent to the drive, that tells you if you can skip
> the cache flush ?

Thought about that and querying power state before doing shutdown 
sequence but things get somewhat ugly because shutdown sequence is 
driven from sd->shutdown().  We'll have to snoop both sync and shutdown 
commands and check whether the system is shutting down.  Also, I felt 
very uneasy about faking successful completion to SYNCHRONIZE_CACHE.

I dunno.  It's already too late for 2.6.21.  I was hoping we could get 
distros to update shutdown utilities in not-too-distant future but I 
have no experience with that.  Is that just a wishful thinking?

-- 
tejun
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