linux-kernel - Re: [PATCH 0/3 -mm] kexec jump -v8

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Date:	Wed, 26 Dec 2007 20:57:16 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	"Huang, Ying" <ying.huang@...el.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Machek <pavel@....cz>, nigel@...el.suspend2.net,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-pm@...ts.linux-foundation.org,
	Kexec Mailing List <kexec@...ts.infradead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3 -mm] kexec jump -v8

On Fri, Dec 21, 2007 at 03:33:19PM +0800, Huang, Ying wrote:

[..]
> The following user-space tools can be used with kexec jump.
> 
> 1. 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_v8/kexec-tools/kexec-tools-src_git_kh8.tar.bz2
>        patches: http://khibernation.sourceforge.net/download/release_v8/kexec-tools/kexec-tools-patches_git_kh8.tar.bz2
>        binary: http://khibernation.sourceforge.net/download/release_v8/kexec-tools/kexec_git_kh8
> 
> 2. 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_v8/makedumpfile/makedumpfile-src_cvs_kh8.tar.bz2
>        patches: http://khibernation.sourceforge.net/download/release_v8/makedumpfile/makedumpfile-patches_cvs_kh8.tar.bz2
>        binary: http://khibernation.sourceforge.net/download/release_v8/makedumpfile/makedumpfile_cvs_kh8
> 
> 3. A simplest memory image restoring tool named "krestore" is
>    implemented. It can be downloaded from the following URL:
>        source: http://khibernation.sourceforge.net/download/release_v8/krestore/krestore-src_cvs_kh8.tar.bz2
>        binary: http://khibernation.sourceforge.net/download/release_v8/krestore/krestore_cvs_kh8
> 
> 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_v8/initramfs/rootfs_cvs_kh8.gz
> All user space tools above are included in the initramfs image.
> 
> 
> Usage example of jumping between original and kexeced kernel:
> 
> 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, or download the
>    pre-built initramfs image, called rootfs.gz in following text.
> 
> 3. Boot kernel compiled in step 1.
> 
> 4. Load kernel compiled in step 1 with /sbin/kexec. If You want to use
>    "krestore" tool, the --elf64-core-headers should be specified in
>    command line of /sbin/kexec. The shell command line can be as
>    follow:
> 
>    /sbin/kexec --load-jump-back /boot/bzImage --mem-min=0x100000
>      --mem-max=0xffffff --elf64-core-headers --initrd=rootfs.gz
> 
> 5. Boot the kexeced kernel with following shell command line:
> 
>    /sbin/kexec -e
> 
> 6. The kexeced kernel will boot as normal kexec. In kexeced kernel the
>    memory image of original kernel can read via /proc/vmcore or
>    /dev/oldmem, and can be written via /dev/oldmem. You can
>    save/restore/modify it as you want to.
> 
> 7. Prepare jumping back from kexeced kernel with following shell
>    command lines:
> 
>    jump_back_entry=`cat /proc/cmdline | tr ' ' '\n' | grep kexec_jump_back_entry | cut -d '='`
>    /sbin/kexec --load-jump-back-helper=$jump_back_entry
> 
> 8. Jump back to the original kernel with following shell command line:
> 
>    /sbin/kexec -e
> 
> 9. Now, you are in the original kernel again. You can read/write the
>    memory image of kexeced kernel via /proc/kimgcore.
> 

Why do we need two interfaces, /proc/vmcore and /proc/kimgcore? Can't
we have just one say /proc/vmcore. Irrespective of what kernel you are
in /proc/vmcore gives you the access to the memory of kernel which was
previously booted.

Thanks
Vivek
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