linux-kernel - Re: [linux-pm] [PATCH] Remove process freezer from suspend to RAM pathway

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Date:	Tue, 3 Jul 2007 18:21:42 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Matthew Garrett <mjg59@...f.ucam.org>
cc:	linux-kernel@...r.kernel.org, <linux-pm@...ts.linux-foundation.org>
Subject: Re: [linux-pm] [PATCH] Remove process freezer from suspend to RAM
 pathway

On Tue, 3 Jul 2007, Matthew Garrett wrote:

> On Tue, Jul 03, 2007 at 05:16:37PM -0400, Alan Stern wrote:
> > On Tue, 3 Jul 2007, Matthew Garrett wrote:
> > > But that's fine - "Are we undergoing a systemwide suspend" is an easy 
> > > question to ask. Freezing processes instead means that most of those 
> > > paths will never be tested.
> > 
> > The question is easy to ask, but it's not so easy to figure out what
> > you should do if the answer is Yes.  Freezing processes instead means
> > that those "untested" paths -- in many, many drivers -- won't have to 
> > exist at all.
> 
> We're used to the idea of applications blocking when a resource they're 
> using goes away - NFS has done it forever. 

You persist in evading my point.  I'm not worried about applications;  
I'm worried about drivers.

Let me put it explicitly: You're writing a driver.  You're working on
the read, write, or probe method.  You add code to check if a system
sleep is underway.  Suppose the answer is Yes -- what does your driver
do next?

Make your answer as detailed as you reasonably can.  And be careful to 
arrange things so that an ongoing I/O operation doesn't get messed up 
when your suspend method is called.

Alan Stern

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