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Date:      Thu, 19 Jul 2007 09:17:48 +0200
From:      "[LoN]Kamikaze" <LoN_Kamikaze@gmx.de>
To:        Norberto Meijome <freebsd@meijome.net>
Cc:        josh@tcbug.org, olli@lurza.secnetix.de, freebsd-stable@FreeBSD.ORG, idiotbg@gmail.com
Subject:   Re: removing external usb hdd without unmounting causes reboot?
Message-ID:  <469F101C.5060906@gmx.de>
In-Reply-To: <20070719130252.6880b967@localhost>
References:  <200707181703.07480.idiotbg@gmail.com>	<200707181541.l6IFf4ht051775@lurza.secnetix.de> <20070719130252.6880b967@localhost>

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Norberto Meijome wrote:
> On Wed, 18 Jul 2007 17:41:04 +0200 (CEST)
> Oliver Fromme <olli@lurza.secnetix.de> wrote:
>> another work-around
>> is to use the auto mounter daemon (amd(8)).  It umounts
>> file systems automatically that are not in use.
>> Another nice feature of amd(8) is that you don't have
>> to mount the file system either -- Simply plug the USB
>> stick in, then access it, and amd(8) will automatically
>> mount it for you.
> 
> 
> Now, something I dont understand  -  amd runs
> at user level, and it mounts filesystems, and nothing dies when the filesystems
> go away (other than the obvious cases for the applications trying to write to
> the FS in question). Doesn't amd , at some point , have to tell the kernel
> 'please mount this filesystem' here or there? Isn't the kernel STILL involved
> in all this? and why doesnt the kernel panic when the FS goes away? 
> 

The trick is that amd unmounts the device after a couple of seconds, so when
someone accidentally removes a usb drive, it doesn't really matter. Amd will
simply fail to mount it on the next access. If you remove the device during or
shortly after accessing it, it still will panic the system.



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