linux-kernel - Re: [RFC/PATCH] usb-storage: wait for device scanning before mounting root

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Date:	Thu, 19 Jun 2008 22:34:33 +0200
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Matthew Wilcox <matthew@....cx>
CC:	Pekka J Enberg <penberg@...helsinki.fi>,
	Alan Stern <stern@...land.harvard.edu>,
	linux-kernel@...r.kernel.org, dsd@...too.org,
	mdharm-usb@...-eyed-alien.net, linux-usb@...r.kernel.org,
	vegardno@....uio.no, James.Bottomley@...senPartnership.com,
	linux-scsi@...r.kernel.org, Greg KH <greg@...ah.com>
Subject: Re: [RFC/PATCH] usb-storage: wait for device scanning before mounting
 root

Matthew Wilcox wrote:
> On Thu, Jun 19, 2008 at 09:54:06PM +0200, Stefan Richter wrote:
>> When to say "I've finished scanning"? --- I think the answer is:  When
>> (a) probing of a configurable number of SCSI targets or logical units
>> was finished or (b) a configurable timeout occurs, whatever of the two
>> happens first.
...
> Yes, I do see the problem.  There's no way the SCSI core can know when
> a driver has finished scanning, so I've punted to the driver to set its
> own timeout here.

This can of course (and frequently is) implemented in userspace, but
requires an initrd.  I'm not up to speed how scsi_wait_scan is put to
use --- it can be used without initrd, can't it?

> I know that new devices really can show up at any
> time, but I think it's reasonable to say that if a machine is booted
> with the same configuration as last time, the drives should show up with
> the same names.

I know that is not what you meant here, but...:

They do show up with the same target identifiers and logical unit
identifiers.  The SCSI core doesn't pass the identifiers through to
userland though.  (Couldn't resist to go off-subject.  Sorry.)
-- 
Stefan Richter
-=====-==--- -==- =--==
http://arcgraph.de/sr/
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