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Date: Tue, 9 Jan 2007 20:17:08 +0530
From: Vivek Goyal <vgoyal@in.ibm.com>
To: Horms <horms@verge.net.au>
Cc: linux kernel mailing list <linux-kernel@vger.kernel.org>,
       Fastboot mailing list <fastboot@lists.osdl.org>,
       Morton Andrew Morton <akpm@osdl.org>, Mohan Kumar M <mohan@in.ibm.com>
Subject: Re: [PATCH] Kdump documentation update for 2.6.20
Message-ID: <20070109144708.GA6924@in.ibm.com>
Reply-To: vgoyal@in.ibm.com
References: <20070108075803.GB7889@in.ibm.com> <20070109011846.GB7479@verge.net.au>
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On Tue, Jan 09, 2007 at 10:18:47AM +0900, Horms wrote:
> >  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.
> 
Hi Horms,

Thanks for going through the update. Actually I never knew that kdump
IA64 support is mainline now. I thought it is still in Tony's tree. And
we never had IA64 specific documentation in kdump.txt file and that's another
reason that discussion became more i386 centric when it came to relocatable
kernels.

> 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 have tried to re-arrange the documentation based on some of your 
recommendations. I have also left couple of sections empty which are
ia64 specific. I don't have an IA64 machine and I don't know how exactly
it is used on IA64. Can you please have a quick look at the patch and
also fill IA64 specific details where appropriate.

Hopefully, this time documentation is clearer.


Mohan, Can you please check the correctness of ppc64 specific details.

> > +   --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.
> 

I am hoping it --args-linux will be required while loading vmlinux on
IA64? Because this is ELF file specific option. And this interface should
be common across all the architectures.

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


Thanks
Vivek


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.
	- Also add kdump on ia64 specific details.

Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
---

 Documentation/kdump/kdump.txt |  221 +++++++++++++++++++++++++++++-------------
 1 file changed, 153 insertions(+), 68 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 12:32:55.000000000 +0530
+++ linux-2.6.20-rc2-mm1-reloc-root/Documentation/kdump/kdump.txt	2007-01-09 19:57:06.000000000 +0530
@@ -17,7 +17,7 @@ You can use common Linux commands, such 
 memory image to a dump file on the local disk, or across the network to
 a remote system.
 
-Kdump and kexec are currently supported on the x86, x86_64, and ppc64
+Kdump and kexec are currently supported on the x86, x86_64, ppc64 and IA64
 architectures.
 
 When the system kernel boots, it reserves a small section of memory for
@@ -54,59 +54,64 @@ 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:
+Note: Latest kexec-tools-testing git tree is available at
 
-   http://lse.sourceforge.net/kdump/
+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
 
-   (This location is being used until all the user-space Kdump patches
-   are integrated with the kexec-tools package.)
-
-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
-------------------------------------------------------
+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) Or use the system kernel binary itself as dump-capture kernel and there is
+   no need to build a separate dump-capture kernel. This is possible
+   only with the architecutres which support a relocatable kernel. As
+   of today i386 and ia64 architectures support relocatable kernel.
+
+Building a relocatable kernel is advantageous from the point of view that
+one does not have to build a second kernel for capturing the dump. But
+at the same time one might want to build a custom dump capture kernel
+suitable to his needs.
 
-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:
+Following are the configuration setting required for system and
+dump-capture kernels for enabling kdump support.
 
-System kernel
--------------
+System kernel config options
+----------------------------
 
 1) Enable "kexec system call" in "Processor type and features."
 
@@ -132,88 +137,169 @@ System kernel
    analysis tools require a vmlinux with debug symbols in order to read
    and analyze a dump file.
 
-4) Make and install the kernel and its modules. Update the boot loader
-   (such as grub, yaboot, or lilo) configuration files as necessary.
+Dump-capture kernel config options (Arch Independent)
+-----------------------------------------------------
 
-5) 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.
+1) Enable "kernel crash dumps" support under "Processor type and
+   features":
 
-   On x86 and x86_64, use "crashkernel=64M@16M".
+   CONFIG_CRASH_DUMP=y
 
-   On ppc64, use "crashkernel=128M@32M".
+2) 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.)
+
+Dump-capture kernel config options (Arch Dependent, i386)
+--------------------------------------------------------
+1) On x86, enable high memory support under "Processor type and
+   features":
 
+   CONFIG_HIGHMEM64G=y
+   or
+   CONFIG_HIGHMEM4G
 
-The dump-capture kernel
------------------------
+2) On x86 and x86_64, disable symmetric multi-processing support
+   under "Processor type and features":
 
-1) Under "General setup," append "-kdump" to the current string in
-   "Local version."
+   CONFIG_SMP=n
 
-2) On x86, enable high memory support under "Processor type and
+   (If CONFIG_SMP=y, then specify maxcpus=1 on the kernel command line
+   when loading the dump-capture kernel, see section "Load the Dump-capture
+   Kernel".)
+
+3) If one wants to build and use a relocatable kernel,
+   Enable "Build a relocatable kernel" support under "Processor type and
+   features"
+
+   CONFIG_RELOCATABLE=y
+
+4) Use a suitable value for "Physical address where the kernel is
+   loaded" (under "Processor type and features"). This only appears when
+   "kernel crash dumps" is enabled. A suitable value depends upon
+   whether kernel is relocatable or not.
+
+   If you are using a relocatable kernel use CONFIG_PHYSICAL_START=0x100000
+   This will compile the kernel for physical address 1MB, but given the fact
+   kernel is relocatable, it can be run from any physical address hence
+   kexec boot loader will load it in memory region reserved for dump-capture
+   kernel.
+
+   Otherwise it should be the start of memory region reserved for
+   second kernel using boot parameter "crashkernel=Y@X". Here X is
+   start of memory region reserved for dump-capture kernel.
+   Generally X is 16MB (0x1000000). So you can set
+   CONFIG_PHYSICAL_START=0x1000000
+
+5) Make and install the kernel and its modules. DO NOT add this kernel
+   to the boot loader configuration files.
+  
+Dump-capture kernel config options (Arch Dependent, x86_64)
+----------------------------------------------------------
+1) On x86, enable high memory support under "Processor type and
    features":
 
    CONFIG_HIGHMEM64G=y
    or
    CONFIG_HIGHMEM4G
 
-3) On x86 and x86_64, disable symmetric multi-processing support
+2) On x86 and x86_64, disable symmetric multi-processing support
    under "Processor type and features":
 
    CONFIG_SMP=n
+
    (If CONFIG_SMP=y, then specify maxcpus=1 on the kernel command line
    when loading the dump-capture kernel, see section "Load the Dump-capture
    Kernel".)
 
-4) On ppc64, disable NUMA support and enable EMBEDDED support:
+3) Use a suitable value for "Physical address where the kernel is
+   loaded" (under "Processor type and features"). This only appears when
+   "kernel crash dumps" is enabled. By default this value is 0x1000000
+   (16MB). It should be the same as X in the "crashkernel=Y@X" boot
+   parameter.
+
+   For x86_64, normally "CONFIG_PHYSICAL_START=0x1000000".
+
+4) Make and install the kernel and its modules. DO NOT add this kernel
+   to the boot loader configuration files.
+
+Dump-capture kernel config options (Arch Dependent, ppc64)
+----------------------------------------------------------
+
+1) On ppc64, disable NUMA support and enable EMBEDDED support:
 
    CONFIG_NUMA=n
    CONFIG_EMBEDDED=y
    CONFIG_EEH=N for the dump-capture kernel
 
-5) Enable "kernel crash dumps" support under "Processor type and
-   features":
-
-   CONFIG_CRASH_DUMP=y
-
-6) Use a suitable value for "Physical address where the kernel is
+2) Use a suitable value for "Physical address where the kernel is
    loaded" (under "Processor type and features"). This only appears when
    "kernel crash dumps" is enabled. By default this value is 0x1000000
    (16MB). It should be the same as X in the "crashkernel=Y@X" boot
    parameter discussed above.
 
-   On x86 and x86_64, use "CONFIG_PHYSICAL_START=0x1000000".
-
    On ppc64 the value is automatically set at 32MB when
    CONFIG_CRASH_DUMP is set.
 
-6) Optionally enable "/proc/vmcore support" under "Filesystems" ->
-   "Pseudo filesystems".
+3) Make and install the kernel and its modules. DO NOT add this kernel
+   to the boot loader configuration files.
 
-   CONFIG_PROC_VMCORE=y
-   (CONFIG_PROC_VMCORE is set by default when CONFIG_CRASH_DUMP is selected.)
+Dump-capture kernel config options (Arch Dependent, ia64)
+----------------------------------------------------------
+(To be filled)
 
-7) Make and install the kernel and its modules. DO NOT add this kernel
-   to the boot loader configuration files.
 
+Boot into System Kernel
+=======================
+
+1) Make and install the kernel and its modules. Update the boot loader
+   (such as grub, yaboot, or lilo) configuration files as necessary.
+
+2) 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 (16MB) for the dump-capture kernel.
+
+   On x86 and x86_64, use "crashkernel=64M@16M".
+
+   On ppc64, use "crashkernel=128M@32M".
 
 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.
+
+Based on the architecture and type of image (relocatable or not), one
+can choose to load the uncompressed vmlinux or compressed bzImage/vmlinuz
+of dump-capture kernel. Following is the summary.
+
+For i386:
+	- Use vmlinux if kernel is not relocatable.
+	- Use bzImage/vmlinuz if kernel is relocatable.
+For x86_64:
+	- Use vmlinux
+For ppc64:
+	- Use vmlinux
+For ia64:
+	(To be filled)
 
-   kexec -p <dump-capture-kernel> \
+If you are using a uncompressed vmlinux image 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 compressed bzImage/vmlinuz, then use following command
+to load dump-capture kernel.
 
-Notes on loading the dump-capture kernel:
+   kexec -p <dump-capture-kernel-bzImage> \
+   --initrd=<initrd-for-dump-capture-kernel> \
+   --append="root=<root-dev> init 1 irqpoll maxcpus=1"
 
-* <dump-capture-kernel> must be a vmlinux image (that is, an
-  uncompressed ELF image). bzImage does not work at this time.
+Notes on loading the dump-capture kernel:
 
 * By default, the ELF headers are stored in ELF64 format to support
   systems with more than 4GB memory. The --elf32-core-headers option can
@@ -231,7 +317,6 @@ Notes on loading the dump-capture kernel
 * "init 1" boots the dump-capture kernel into single-user mode without
   networking. If you want networking, use "init 3."
 
-
 Kernel Panic
 ============
 
_
-
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