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_KEXEC=y
CONFIG_CRASH_DUMP=y # only needed by kexeced kernel to save/restore memory image
CONFIG_PM=y
CONFIG_KEXEC_JUMP=y
2. Download the kexec-tools-testing git tree, apply the kexec-tools
kjump patches (or download the source tar ball directly) and
compile.
3. Download and compile the krestore tool.
4. Prepare 2 root partition used by kernel A and kernel B/C, referred
as /dev/hda, /dev/hdb in following text. This is not strictly
necessary, I use this scheme for testing during development.
5. Boot kernel compiled for normal usage (kernal A).
6. Load kernel compiled for hibernating/restore usage (kernel B) with
kexec, the same kernel as that of 5 can be used if
CONFIG_RELOCATABLE=y and CONFIG_CRASH_DUMP=y are selected.
The --elf64-core-headers should be specified in command line of
kexec, because only the 64bit ELF is supported by krestore tool.
For example, the shell command line can be as follow:
kexec -p -n /boot/bzImage --mem-min=0x100000 --mem-max=0xffffff
--elf64-core-headers --append="root=/dev/hdb single"
7. Jump to the hibernating kernel (kernel B) with following shell
command line:
kexec -j
8. In the hibernating kernel (kernel B), the memory image of
hibernated kernel (kernel A) can be saved as follow:
cp /proc/vmcore .
cp /sys/kernel/kexec_jump_back_entry .
Here we save also kernel B's pages.
9. Shutdown or reboot in hibernating kernel (kernel B).
10. Boot kernel (kernel C) compiled for hibernating/restore usage on
the root file system /dev/hdb in memory range of kernel B.
For example, the following kernel command line parameters can be
used:
root=/dev/hdb single memmap=exactmap memmap=640K@0K memmap=15M@1M
0-640K from kernel A overrides 0-640K of kernel C at restore time.
11. In restore kernel (kernel C), the memory image of kernel A can be
restored as follow:
cp kexec_jump_back_entry /sys/kernel/kexec_jump_back_entry
krestore vmcore
This steps replaces kernel C's pages with kernel B's (at least 15m-16m),
saved at step 8, so these kernels should be equal? Or they must be
physically located in non-overlapping regions such that C is in B's
memory range but non-overlapping. The proposed setup doesn't guaratee
this afaics.
12. Jump back to hibernated kernel (kernel A)
kexec -b
Best Regards,
Huang Ying
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--Mika
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