Re: [PATCH] Kdump documentation update for 2.6.20

[Horms <horms@verge.net.au>]

On Mon, Jan 08, 2007 at 01:28:03PM +0530, Vivek Goyal wrote:
> 
> 
> 
> o Kdump documentation update.
> 	- Update details for using relocatable kernel.
> 	- Start using kexec-tools-testing release as it is latest and old
> 	  kexec-tools can't load relocatable bzImage file.
> 
> Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
> ---
> 
>  Documentation/kdump/kdump.txt |  160 ++++++++++++++++++++++++++++++++++--------
>  1 file changed, 130 insertions(+), 30 deletions(-)
> 
> diff -puN Documentation/kdump/kdump.txt~kdump-documentation-update Documentation/kdump/kdump.txt
> --- linux-2.6.20-rc2-mm1-reloc/Documentation/kdump/kdump.txt~kdump-documentation-update	2007-01-08 10:01:50.000000000 +0530
> +++ linux-2.6.20-rc2-mm1-reloc-root/Documentation/kdump/kdump.txt	2007-01-08 11:51:49.000000000 +0530
> @@ -54,56 +54,68 @@ memory," in two ways:
>  Setup and Installation
>  ======================
>  
> -Install kexec-tools and the Kdump patch
> ----------------------------------------
> +Install kexec-tools
> +-------------------
>  
>  1) Login as the root user.
>  
>  2) Download the kexec-tools user-space package from the following URL:
>  
> -   http://www.xmission.com/~ebiederm/files/kexec/kexec-tools-1.101.tar.gz
> +http://www.kernel.org/pub/linux/kernel/people/horms/kexec-tools/kexec-tools-testing-20061214.tar.gz
>  
> -3) Unpack the tarball with the tar command, as follows:
> -
> -   tar xvpzf kexec-tools-1.101.tar.gz
> -
> -4) Download the latest consolidated Kdump patch from the following URL:
> -
> -   http://lse.sourceforge.net/kdump/
> +Note: Latest kexec-tools-testing git tree is available at
>  
> -   (This location is being used until all the user-space Kdump patches
> -   are integrated with the kexec-tools package.)
> +git://git.kernel.org/pub/scm/linux/kernel/git/horms/kexec-tools-testing.git
> +or
> +http://www.kernel.org/git/?p=linux/kernel/git/horms/kexec-tools-testing.git;a=summary
>  
> -5) Change to the kexec-tools-1.101 directory, as follows:
> +3) Unpack the tarball with the tar command, as follows:
>  
> -   cd kexec-tools-1.101
> +   tar xvpzf kexec-tools-testing-20061214.tar.gz
>  
> -6) Apply the consolidated patch to the kexec-tools-1.101 source tree
> -   with the patch command, as follows. (Modify the path to the downloaded
> -   patch as necessary.)
> +4) Change to the kexec-tools-1.101 directory, as follows:
>  
> -   patch -p1 < /path-to-kdump-patch/kexec-tools-1.101-kdump.patch
> +   cd kexec-tools-testing-20061214
>  
> -7) Configure the package, as follows:
> +5) Configure the package, as follows:
>  
>     ./configure
>  
> -8) Compile the package, as follows:
> +6) Compile the package, as follows:
>  
>     make
>  
> -9) Install the package, as follows:
> +7) Install the package, as follows:
>  
>     make install
>  
>  
>  Download and build the system and dump-capture kernels
>  ------------------------------------------------------
> +There are two possible methods of using Kdump.
> +
> +	1) Build a separate custom dump-capture kernel for capturing the
> +	   kernel core dump.
> +
> +	2) Use system kernel itself as dump-capture kernel and there is
> +	   no need to build a separate dump-capture kernel. (Only for
> +	   i386 architecture kernel version 2.6.20 onwards)
> +
> +For i386, second method is recommended, as it takes away the need to build
> +additional kernel.

I think that the above description is a little misleading, and quite
i386 centric. The question is not weather or not you are using the
system kernel, but rather, what options are needed for the crash kernel.

In terms of a non-relocatable kernel, then the boot and crash kernels
need to be separate.

But in the case of a relocatable kernel, then the boot and crash kernels
may be the same, or they may be separate. Depending on just what
the end-user wants in each kernel.

On ia64 there is no CONFIG_RELOCATABLE option, but the kernel is always
relocatable anyway. That is, you can use the same kernel before and
after crash (though I am not sure that I have tested this).

I'm not sure about ppc64.

I think that the description of how to build the kernels also needs to
be reworked a little to reflect this. Perhaps you could divide the
methods based on vmlinuz/bzImage, rather than
non-relocatable/relocatable (or custom kernel/system kernel?). It seems
that it is the former, rather than the later that has impact on how
things work.

> +
> +If you decide to use second option (Relocatable kernel), then directly jump to
> +the section "Method 2".
> +
> +Method 1:
> +--------
>  
>  Download the mainline (vanilla) kernel source code (2.6.13-rc1 or newer)
> -from http://www.kernel.org. Two kernels must be built: a system kernel
> -and a dump-capture kernel. Use the following steps to configure these
> -kernels with the necessary kexec and Kdump features:
> +from http://www.kernel.org.
> +
> +Two kernels must be built: a system kernel and a dump-capture kernel.
> +Use the following steps to configure these kernels with the necessary kexec
> +and Kdump features:
>  
>  System kernel
>  -------------
> @@ -198,22 +210,110 @@ The dump-capture kernel
>  7) Make and install the kernel and its modules. DO NOT add this kernel
>     to the boot loader configuration files.
>  
> +Skip following section and directly jump to "Load the Dump-capture Kernel"
> +section.
> +
> +Method 2:
> +--------
> +
> +Build Relocatable bzImage for dump-capture kernel (i386 only)
> +------------------------------------------------------------
> +Kernel version 2.6.20 onwards, i386 kernel bzImage has become relocatable.
> +That means, same kernel binary bzImage can be run from any physical address.
> +This takes away the limitation of building a special dump-capture kernel
> +compiled for a specific memory location for capturing the dump. Now one
> +has the flexibility of using the system kernel itself as the dump capture
> +kernel for i386.
> +
> +Download the mainline (vanilla) kernel source code (2.6.20-rc1 or newer)
> +from http://www.kernel.org.
> +
> +1) Enable "kexec system call" in "Processor type and features."
> +
> +   CONFIG_KEXEC=y
> +
> +2) Enable "kernel crash dumps" support under "Processor type and
> +   features"
> +
> +   CONFIG_CRASH_DUMP=y
> +
> +   Leave "Physical address where the kernel is loaded" unchanged. By
> +   default it is set to 0x100000 (1MB).
> +
> +3) Enable "Build a relocatable kernel" support under "Processor type and
> +   features"
> +
> +   CONFIG_RELOCATABLE=y
> +
> +4) Enable "/proc/vmcore support" under "Filesystems" -> "Pseudo filesystems".
> +
> +   CONFIG_PROC_VMCORE=y
> +   (CONFIG_PROC_VMCORE is set by default when CONFIG_CRASH_DUMP is selected.)
> +
> +5) On x86, enable high memory support under "Processor type and
> +   features":
> +
> +   CONFIG_HIGHMEM64G=y
> +   or
> +   CONFIG_HIGHMEM4G
> +
> +6) Enable "Compile the kernel with debug info" in "Kernel hacking."
> +
> +   CONFIG_DEBUG_INFO=Y
> +
> +   This causes the kernel to be built with debug symbols. The dump
> +   analysis tools require a vmlinux with debug symbols in order to read
> +   and analyze a dump file.
> +
> +7) Enable "sysfs file system support" in "Filesystem" -> "Pseudo
> +   filesystems." This is usually enabled by default.
> +
> +   CONFIG_SYSFS=y
> +
> +   Note that "sysfs file system support" might not appear in the "Pseudo
> +   filesystems" menu if "Configure standard kernel features (for small
> +   systems)" is not enabled in "General Setup." In this case, check the
> +   .config file itself to ensure that sysfs is turned on, as follows:
> +
> +   grep 'CONFIG_SYSFS' .config
> +
> +8) Make and install the kernel and its modules. Update the boot loader
> +   (such as grub, yaboot, or lilo) configuration files as necessary.
> +
> +9) Boot the system kernel with the boot parameter "crashkernel=Y@X",
> +   where Y specifies how much memory to reserve for the dump-capture kernel
> +   and X specifies the beginning of this reserved memory. For example,
> +   "crashkernel=64M@16M" tells the system kernel to reserve 64 MB of memory
> +   starting at physical address 0x01000000 for the dump-capture kernel.
> +
> +   On x86 and x86_64, use "crashkernel=64M@16M".
>  
>  Load the Dump-capture Kernel
>  ============================
>  
> -After booting to the system kernel, load the dump-capture kernel using
> -the following command:
> +After booting to the system kernel, dump-capture kernel needs to be
> +loaded.
>  
> -   kexec -p <dump-capture-kernel> \
> +If you are using a separate dump capture kernel (method 1) then use
> +following command to load dump-capture kernel.
> +
> +   kexec -p <dump-capture-kernel-vmlinux-image> \
>     --initrd=<initrd-for-dump-capture-kernel> --args-linux \
> -   --append="root=<root-dev> init 1 irqpoll"
> +   --append="root=<root-dev> init 1 irqpoll maxcpus=1"
> +
> +If you are using a relocatable kernel (method 2), then use
> +following command.
>  
> +   kexec -p <bzImage-of-relocatable-kernel> \
> +   --initrd=<initrd-for-relocatable-kernel> \
> +   --append="root=<root-dev> init 1 irqpoll maxcpus=1"

--args-linux is not needed on ia64, but its kernel is relocatable.
I think the important point is that if you are using a bzImage,
then you need --args-linux, and basically at this point that
means an i386 (or x86_64) relocatable bzImage.

Then again, I could be wrong, I'm not sure that I understand
--args-linux, I just know that I'm not using it :)

>  Notes on loading the dump-capture kernel:
>  
> -* <dump-capture-kernel> must be a vmlinux image (that is, an
> -  uncompressed ELF image). bzImage does not work at this time.
> +* For method 1, <dump-capture-kernel> must be a vmlinux image.
> +  (that is, an uncompressed ELF image). bzImage does not work at
> +  this time. Using bzImage for dump capture kernel works only for
> +  Relocatable kernel (method 2)
>  
>  * By default, the ELF headers are stored in ELF64 format to support
>    systems with more than 4GB memory. The --elf32-core-headers option can
> _

-- 
Horms
  H: http://www.vergenet.net/~horms/
  W: http://www.valinux.co.jp/en/

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