Re: [PATCH 0/2] Kexec jump: The first step to kexec base hibernation

Rafael J. Wysocki
2007-07-17T14:22:27Z

On Tuesday, 17 July 2007 14:48, Huang, Ying wrote:
> On Tue, 2007-07-17 at 01:13 -0700, david@lang.hm wrote:
> > however, since the resume designed for ACPI won't work would the following
> > approach work
> >
> > 1. boot one kernel
> > 2. setup a kexec the same way you would for hibernate
> > 3. kexec to the new kernel
> > 4. overwrite the memory of the first kernel
> > 5. kexec 'back' to the main kernel that has now been overwritten by what was saved?
> >
> > as part of this question, when you do a kexec, how does the kernel that
> > you are doing the kexec to know what to run next?
>
> For kernel in 3 that do kexec, the devices and CPU state are saved into
> memory before executing the new kernel. So when jumping back, the
> control will continue from kexec point. If the memory image of main
> kernel is restored from disk, the devices and CPU state in memory is
> restored too. Before jumping back in 5, the devices are put in the known
> state, after jumping back, the devices and CPU state is restored. If the
> "kexec -j" is used to trigger the kexec in 3, the system will continue
> with "kexec -j" exiting with exit code 0.
>
> > it needs to do some initialization first before it starts running normal
> > things, and at that point it the move back doesn't look for init like a
> > normal kernel boot (or the system would effectivly boot instead of picking
> > up where it left off)
>
> I think the early initialization can be done in a initramfs. At that
> point, the resume image can be checked, the next step depends on the
> result of checking.
>
> > is this 'restart point' flexible enough that either the pre-hibernate
> > kerenl or the small hibernate kernel could tell the pre-hibernate kernel
> > to go into suspend-to-ram mode before doing anything else?
>
> It is possible for hibernate kernel to pass information back to
> pre-hibernate kernel. For example, the information can be passed in jump
> buffer page.

I think it would be reasonable to have a protocol defined for passing this
information, so that it's independent of the kernel version etc.

Greetings,
Rafael

--
"Premature optimization is the root of all evil." - Donald Knuth