Re: [PATCH -mm 2/2] kexec jump -v11: save/restore device state

On Tue, Jun 10, 2008 at 03:15:06PM +0800, Huang, Ying wrote:

This patch implements devices state save/restore before after kexec.


This patch together with features in kexec_jump patch can be used for
following:

- A simple hibernation implementation without ACPI support. You can
  kexec a hibernating kernel, save the memory image of original system
  and shutdown the system. When resuming, you restore the memory image
  of original system via ordinary kexec load then jump back.

- Kernel/system debug through making system snapshot. You can make
  system snapshot, jump back, do some thing and make another system
  snapshot.

- Cooperative multi-kernel/system. With kexec jump, you can switch
  between several kernels/systems quickly without boot process except
  the first time. This appears like swap a whole kernel/system out/in.

- A general method to call program in physical mode (paging turning
  off). This can be used to invoke BIOS code under Linux.


The following user-space tools can be used with kexec jump:

- kexec-tools needs to be patched to support kexec jump. The patches
  and the precompiled kexec can be download from the following URL:
       source: http://khibernation.sourceforge.net/download/release_v10/kexec-tools/kexec-tools-src_git_kh10.tar.bz2
       patches: http://khibernation.sourceforge.net/download/release_v10/kexec-tools/kexec-tools-patches_git_kh10.tar.bz2
       binary: http://khibernation.sourceforge.net/download/release_v10/kexec-tools/kexec_git_kh10

- makedumpfile with patches are used as memory image saving tool, it
  can exclude free pages from original kernel memory image file. The
  patches and the precompiled makedumpfile can be download from the
  following URL:
       source: http://khibernation.sourceforge.net/download/release_v10/makedumpfile/makedumpfile-src_cvs_kh10.tar.bz2
       patches: http://khibernation.sourceforge.net/download/release_v10/makedumpfile/makedumpfile-patches_cvs_kh10.tar.bz2
       binary: http://khibernation.sourceforge.net/download/release_v10/makedumpfile/makedumpfile_cvs_kh10

- An initramfs image can be used as the root file system of kexeced
  kernel. An initramfs image built with "BuildRoot" can be downloaded
  from the following URL:
       initramfs image: http://khibernation.sourceforge.net/download/release_v10/initramfs/rootfs_cvs_kh10.gz
  All user space tools above are included in the initramfs image.


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.

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.


[..]

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.

Thanks
Vivek