linux-kernel - Re: SATA hotplug from the user side ?

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Message-ID: <45AAE52B.2070705@gmail.com>
Date:	Mon, 15 Jan 2007 11:21:31 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Soeren Sonnenburg <kernel@....de>
CC:	Jeff Garzik <jeff@...zik.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: SATA hotplug from the user side ?

Soeren Sonnenburg wrote:
> Jeff & Tejun thanks *a lot* for clarifying this. I am quite happy to see
> that this is working very reliably!

You're welcome.  :-)

>>> These messages sound eval - so now the question is should I care ?
>>> ( On the other hand it did not crash the machine )
>> So, no, you don't really have to care.  Just make sure the device is
>> unmounted prior to unplugging.
> 
> OK, but then this really should be in the SATA hotplug FAQ (or can one
> fix this somehow?)... No user will ignore messages like this. What is

Yeah, probably.  Care to submit patch to FAQ to Jeff?

> especially annoying is that udev on the first remove/insert cycle
> created a new device node so the disk became /dev/sde (was /dev/sdd):
> dmesg output of reinserting the disk 2 times follows:

That's because something is still holding onto /dev/sdd.  The device
remains dangled until all references to it are gone.  /dev/sdd is still
lingering when the drive is hotplugged; thus, it gets assigned the next
device.

I think this is best solved by udev.  Think of /dev/sdX as kernel
internal name which may change from time to time.  Mount devices with
LABEL's and use udev-provided persistent names to access removable
devices.  Also, libata can be improved to tell udev that certain ports
are external, I think.

Thanks.

-- 
tejun
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