On Sat, 14 Jul 2007, Rafael J. Wysocki wrote:
On Saturday, 14 July 2007 22:34, [email protected] wrote:
in the past, Rafael J. Wysocki wrote:
BTW, please read this message and tell me what you think:
http://lkml.org/lkml/2007/7/13/265
Greetings,
Rafael
since I've deleted this message here's the relavent portion of it
Okay, I have thought it through and I think that, as an initial step, we
can do something like this:
- preload the image-saving kernel before hibernation
- in the hibernation code path replace device_suspend() with the shutting
down of all devices without unregistering them (not very nice, but should be
sufficient for a while)
- when we've called device_power_down() and save_processor_state(), jump
to the image-saving kernel and let it run
- make the image-saving kernel set up everything, save the image without
starting any user space (we may use the existing image-saving code for
this purpose, with some modifications) and power off the system (or make it
enter S4)
- use the existing restoration code to load the image and jump to the
hibernated kernel
- in the restore code patch replace device_resume() with the reprobing of
all devices.
Comments?
I think this is far more complicated then it needs to be.
it sounds like it should be possible to do the following
1. figure out what pages should be backed up (creating a data structure to
hold them)
That should be done after step 2, because the memory contents can change
in this step.
no, this needs to be done by the main kernel, becouse only it knows how to
find this info. the kernel that you kexec into could be very different
(including different versions) and the ways to identify this data is not
part of any existing API
2. kexec into the hibernate kernel (this step handles all device
transitions today)
3. have the hibernate userspace find the data structures created in step
#1
4. have the hibernate userspace write the pages somewhere in the suspend
format.
You don't need to run any hibernate userspace to carry out steps 3 and 4.
you should though.
by doing this write in usespace you can add in all the eye-candy (aka
progress bars), network I/O, etc that you want since it doesn't affect
things
trying to do this in the kernel makes the kernel have to know/decide too
much policy (and many things that people want to do are things that do not
belong in the kernel in the first place)
5. have the hibernate kernel power down the box.
the only things here that sounds like they're not available in stock
kernels are steps #1 and #3.
Correct, up to the first remark above.
now this won't do the fancier suspend-to-ram-and-disk and it won't let you
go back from the hibernate kernel to the main kernel, but it should be
enough to let you do the suspend safely and reliably.
for the restore, as I understand it the process is
1. boot a kernel, any working kernel.
2. read the suspend formatted data from wherever it was saved and feed it
to /dev/suspend
Yes, something like this, but you really should pay more attention to devices.
There are things that you shouldn't do to them (like unregistering), because
some processes may be using them while we're trying to hibernate (for now
we have the freezer, but I though you'd like to do all that to eliminate it).
Generally, you need to ensure that the devices are handled in consistent ways
by both the hibernated and image-saving kernels and that's a big piece of the
jigsaw that's missing now.
the kexec process should handle the device state for the transition from
one kernel to another (it has to do this now, this isn't a new
requirement), so this should solve the problem during the hibernate stage.
during the wakeup stage, I thought you said that al that was needed was to
feed the suspend image to /dev/suspend and the kernel in the suspend image
would re-probe, or otherwise re-initialize all the devices it needs. am I
misunderstanding this?
David Lang
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