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    SubjectRe: [PATH 0/1] Kexec jump - v2 - the first step to kexec based hibernation
    On Sunday, 15 July 2007 09:13, Huang, Ying wrote:
    > The changelog between v1 and v2
    > 1. The kexec jump implementation is put into the kexec/kdump
    > framework instead of software suspend framework. The device
    > and CPU state save/restore code of software suspend is called
    > when needed.
    > 2. The same code path is used for both kexec a new kernel and jump
    > back to original kernel.
    > The complete changelog of the patch is as follow:
    > ---
    > Kexec base hibernation has some potential advantages over uswsusp and
    > TuxOnIce (suspend2). Some most obvious advantages are:
    > 1. The hibernation image size can exceed half of memory size easily.

    In TuxOnIce (suspend2) there's no such limitation.

    > 2. The hibernation image can be written to and read from almost
    > anywhere, such as USB disk, NFS.

    You can do this, too, with uswsusp.

    > This patch implements the functionality of "jumping from kexeced
    > kernel to original kernel". That is, the following sequence is
    > possible:
    > 1. Boot a kernel A
    > 2. Work under kernel A
    > 3. Kexec another kernel B in kernel A
    > 4. Work under kernel B
    > 5. Jump from kernel B to kernel A
    > 6. Continue work under kernel A
    > This is the first step to implement kexec based hibernation. If the
    > memory image of kernel A is written to or read from a permanent media
    > in step 4, a preliminary version of kexec based hibernation can be
    > implemented.
    > The kernel B run as a crashdump kernel in reserved memory region. This
    > is the biggest constrains of the patch. It is planed to be eliminated
    > in the future version. That is, instead of reserving memory region
    > previously, the needed memory region is backupped before kexec and
    > restored after jumping back.
    > Another constrains of the patch is that the CONFIG_ACPI must be turned
    > off to make kexec jump work. Because ACPI will put devices into low
    > power state, the kexeced kernel can not be booted properly under
    > it. This constrains can be eliminated by separating the suspend method
    > and hibernate method of the devices as proposed earlier in the LKML.
    > The kexec jump is implemented in the framework of kexec/kdump. In
    > sys_reboot, a new command named LINUX_REBOOT_CMD_KJUMP is defined to
    > trigger the jumping to (executing) the new kernel or jump back to the
    > original kernel.
    > Now, only the i386 architecture is supported. The patch is based on
    > Linux kernel 2.6.22, and has been tested on my IBM T42.
    > Usage:
    > 1. Compile kernel with following options selected:
    > CONFIG_X86_32=y
    > CONFIG_RELOCATABLE=y # not needed strictly, but it is more convenient with it
    > CONFIG_PM=y
    > 2. Compile the kexec-tools with kdump and kjump patches, the
    > kdump patch can be found at:
    > While, the kexec-tools kjump patch is appended with the mail.
    > 3. Boot kernel compiled for normal usage, the reserved crash kernel
    > memory region must be added to kernel command line as following:
    > crashkernel=<XX>M@<XX>M
    > Where, <XX> should be replaced by the real memory size and position.
    > 4. Load kernel compiled for hibernating usage as a crashdump kernel
    > with kexec, the same kernel as that of 3 can be used if
    > CONFIG_RELOCATABLE=y is selected. The kernel command line option as
    > following must be appended to kernel command line.
    > kexec_jump_buf_pfn=`cat /sys/kernel/kexec_jump_buf_pfn`
    > For example, the shell command line can be as follow:
    > kexec -p /boot/vmlinux --args-linux --append="root=/dev/hdb signal
    > kexec_jump_buf_pfn=`cat /sys/kernel/kexec_jump_buf_pfn`"
    > 5. Boot the hibernating kernel with following shell command line:
    > kexec -j
    > 6. In the kexec booted kernel, trigger the jumping back with following
    > shell command.
    > kexec -j

    Well, I think that's _way_ too much complicated to be useful for hibernation
    on systems that are set up and administered by average users.


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