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    SubjectRe: [PATCH -mm 2/2] kexec jump -v11: save/restore device state
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    On Wed, 2008-06-11 at 12:30 -0400, Vivek Goyal wrote:
    [...]
    > > Usage example of simple hibernation:
    > >
    > > 1. Compile and install patched kernel with following options selected:
    > >
    > > CONFIG_X86_32=y
    > > CONFIG_RELOCATABLE=y
    > > CONFIG_KEXEC=y
    > > CONFIG_CRASH_DUMP=y
    > > CONFIG_PM=y
    > >
    > > 2. Build an initramfs image contains kexec-tool and makedumpfile, or
    > > download the pre-built initramfs image, called rootfs.gz in
    > > following text.
    > >
    > > 3. Prepare a partition to save memory image of original kernel, called
    > > hibernating partition in following text.
    > >
    > > 4. Boot kernel compiled in step 1 (kernel A).
    > >
    > > 5. In the kernel A, load kernel compiled in step 1 (kernel B) with
    > > /sbin/kexec. The shell command line can be as follow:
    > >
    > > /sbin/kexec --load-preserve-context /boot/bzImage --mem-min=0x100000
    > > --mem-max=0xffffff --initrd=rootfs.gz
    > >
    > > 6. Boot the kernel B with following shell command line:
    > >
    > > /sbin/kexec -e
    > >
    > > 7. The kernel B will boot as normal kexec. In kernel B the memory
    > > image of kernel A can be saved into hibernating partition as
    > > follow:
    > >
    > > jump_back_entry=`cat /proc/cmdline | tr ' ' '\n' | grep kexec_jump_back_entry | cut -d '='`
    > > echo $jump_back_entry > kexec_jump_back_entry
    > > cp /proc/vmcore dump.elf
    > >
    > > Then you can shutdown the machine as normal.
    > >
    > > 8. Boot kernel compiled in step 1 (kernel C). Use the rootfs.gz as
    > > root file system.
    > >
    >
    > One of the concerns raised by hibernation people in the past was to use
    > single boot loader entry to boot normally as well while resuming a kernel.
    >
    > So in this case a user either needs to maintain two boot-loader entries
    > or modify it on the fly. I wished there was a better way to handle that.

    Now it is not needed to have two boot-loader entries, just one is
    enough. Step 4 and step 8 can share the same boot-loader entries. The
    rootfs.gz can be the normal initramfs or initrd when deployment. In
    rootfs.gz, if there is a valid hibernation image, the hibernated system
    will be restored, otherwise, normal boot process follows.


    > I am more interested in ability to have multiple kernel loaded in RAM
    > and capability to switch between them. Allows me to take non-disruptive
    > core dumps and somebody wanted to snapshots the kernels. That should
    > still work.
    >
    >
    > [..]
    > > --- a/arch/x86/kernel/machine_kexec_32.c
    > > +++ b/arch/x86/kernel/machine_kexec_32.c
    > > @@ -125,6 +125,12 @@ void machine_kexec(struct kimage *image)
    > > /* Interrupts aren't acceptable while we reboot */
    > > local_irq_disable();
    > >
    > > + if (image->preserve_context) {
    > > +#ifdef CONFIG_X86_IO_APIC
    > > + disable_IO_APIC();
    > > +#endif
    >
    > I think it would be a good idea to put some kind of comment here. We
    > need to put APICs in legacy mode so that we can get timer interrupts
    > in second kernel. kexec/kdump paths already have calls to
    > disable_IO_APIC() in one form or other. kexec jump path also needs one.

    OK. I will add it.

    Best Regards,
    Huang Ying

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