linux-kernel - Re: [linux-pm] [PATCH -mm 1/2] kexec jump -v12: kexec jump

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Date:	Sat, 12 Jul 2008 15:55:02 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>, <nigel@...el.suspend2.net>,
	Kexec Mailing List <kexec@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, Pavel Machek <pavel@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<linux-pm@...ts.linux-foundation.org>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [linux-pm] [PATCH -mm 1/2] kexec jump -v12: kexec jump

On Fri, 11 Jul 2008, Eric W. Biederman wrote:

> > Forcing the second set of requests to filter through an extra software 
> > layer is a clumsy way of accomplishing this.  There ought to be a 
> > better approach.
> 
> The point was something different.  The reasons we can not store the
> state of the system with the hardware devices logically hot unplugged
> (and thus reuse all of the find device hotplug methods) is because
> things like the filesystem layer don't know how to cope with their
> block devices going away an coming back.

This is not how the procedure works.  During hibernation, block devices
are not logically hot-unplugged.  (If they were then they couldn't be
used for writing the memory image.)  Instead, they are quiesced or
suspended and their input queues are plugged.

> That is the problem inserting an virtual software device in the middle
> can solve.  If that works should there be a better way?  Certainly but
> to prove it out starting with a block device wrapper is a trivial way to
> go.

This sounds like a solution to a non-existent problem.

Alan Stern

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