Re: [dm-crypt] dm-crypt LUKS and USB power management

From: Arno Wagner <arno@wagner.name>
To: dm-crypt@saout.de
Subject: Re: [dm-crypt] dm-crypt LUKS and USB power management
Date: Tue, 31 May 2016 20:19:58 +0200	[thread overview]
Message-ID: <20160531181957.GA11489@tansi.org> (raw)
In-Reply-To: <574D6E9A.5070401@gmx.de>

That would be the wrong place to do it. Monitoring USB
disconnect is the task of the USB driver, also because
LUKS/LVM/etc. has no clue what hardware is used on
the lower layers.

Regards,
Arno

On Tue, May 31, 2016 at 12:59:38 CEST, Axel Heider wrote:
> 
> 
> 
> > I doubt if it could be done clean. Most targets in Device Mapper ask for
> > careful unstacking.
> 
> Couldn't LUKS/cryptsetup/dm-crypt set up a monitor for the disk peripheral
> at least? So it releases any connection to the device if it is diconnected.
> The device is gone anyway, so there is no gain in keeping any handles open.
> Internally, the higher layer file system driver should still get errors
> then. But the lower lever driver stack is no longer blocked. So a new
> device can become /dev/sda again and not dev/sdb because /dev/sda is still
> "somehow" active.
> 
> 
> 
> > I would rather investigate the (flaky) USB device. First, does it happen only
> > when Runtime PM is enabled ? If so, you should just blacklist it from Power
> > Management. Many devices, under Linux, report (false) PM capabilities.
> 
> My current solution is using a hub with a dedicated power support to
> connect the USB/SATA adapter with the HDD. Then disk spindown can
> still be used, but there is no USB disconnect/reconnect. That solves
> the problem practically.
> I did not find a way yet to disable power/idele management on the
> board USB ports. It's a Odroid C1 or C2 with Debian Jesse Kernel
> 3.14.29 or 3.14.65. The suggestion from
> http://unix.stackexchange.com/questions/91027/how-to-disable-usb-autosuspend-on-kernel-3-7-10-or-above
> does not work
> and so far nobody else had a solution. Will keep searching...
> 
> Axel
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-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno@wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
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