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Re: Q: Clarification about extra option ..Re: [Xen-devel] Re: [PATCH] pv

To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Subject: Re: Q: Clarification about extra option ..Re: [Xen-devel] Re: [PATCH] pvops: Make suspend work when CONFIG_SUSPEND=n
From: Shriram Rajagopalan <rshriram@xxxxxxxxx>
Date: Fri, 4 Mar 2011 11:49:28 -0800
Cc: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, Jeremy Fitzhardinge <Jeremy.Fitzhardinge@xxxxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>, Frank Pan <frankpzh@xxxxxxxxx>, "Rafael J. Wysocki" <rjw@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On Fri, Mar 4, 2011 at 10:26 AM, Konrad Rzeszutek Wilk
<konrad.wilk@xxxxxxxxxx> wrote:
> .. snip..
>> >>  Someone suggested creating a new user visible hibernate symbol that would
>> >> solve this issue and make the main hibernate logic depend on this symbol 
>> >> rather
>> >> than the HIBERNATE symbol. I could certainly spin up a patch for that but 
>> >> nobody
>> >> seemed to have reached a conclusion.
>> >
>> > Please do. I was under the understanding that we were waiting for a 
>> > victi^H^H^Hvolunteer
>> > to implement that.
>> >
>> > That was the only thing gatting your patchset going in.
>> >
>> >
>> I certainly would have long time ago but for this comment in the thread
>> "xen: fix XEN_SAVE_RESTORE Kconfig dependencies"
>> Rafael:
>>  I think we can introduce CONFIG_HIBERNATE_INTERFACE that will be 
>> user-visible
>> option instead of CONFIG_HIBERNATION and will select the latter.  Then,
>> CONFIG_XEN_SAVE_RESTORE will also be able to select CONFIG_HIBERNATION 
>> without
>> building the hibernate interface in, which will prevent user space from being
>> confused, but that will cause too much code to be built anyway.
>> If by "too much code to be built", he meant the increase in kernel
>> image size, then its not much of a deal :P.
>> But if he meant, "too much code rework", then it is an issue.
> The idea here is that the /sys/power/state won't be exposed with the "disk"
> option.
>> But IMO, the CONFIG_HIBERNATE_INTERFACE needs to go in,
>> only in the main hibernation initiator logic, as we still need the
>> pieces of every driver anyway (their freeze/thaw routines).
> Right. The idea here is to seperate the sysfs interface to be behind
> another config option. So you can still enable the hibernate kernel code
> but without exposing it to the userland.
> Rafael,
> That is the general idea, right?

I was thinking along the lines of
 def_bool n



in kernel/power/Makefile
obj-$(CONFIG_HIBERNATION_INTERFACE)  += hibernate.o snapshot.o swap.o \

  user.o block_io.o

Will this be sufficient to prevent unnecessary code from being built?
Or, is this oversimplified file exclusion totally wrong and I have to
dig deeper?

>From a cursory glance, these files seem to be dealing solely with SWSUSP which
roughly does the following:
 1. freezing devices (using pm_op functions in main.c)
 2. saving memory to swap
 3. thawing on resume (using pm_op functions in main.c)

XEN_SAVE_RESTORE only needs steps 1 & 3.


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