Thin client IBM NetVista N2200 Model 8363 kernel compile for NFS root

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IMPORTANT NOTE: This blog contains several pages related to Linux on the IBM NetVista N2200 (Model 8363). All the information is summarized here:

Linux on the IBM NetVista N2200 (Model 8363) page on Smithfarm - the Brain

Currently on my IBM NetVista N2200, I am booting Linux kernel verion 2.6.31 to a root filesystem exported from a server over NFS ("Root-NFS" for short). Due to the quirky nature of the N2200 hardware and firmware, this was not simple to accomplish.

There are two ways that I know of to do Root-NFS on the N2200: first, you can hard-code the required kernel parameters into the kernel, and second, you can include an initrd inside the kernel. Of these two, the first is much simpler.

When I got started with this Root-NFS project, I first tried to use the 2.6.18 kernel from the PusPus "distribution". After hours of trials, I gave up on getting it to do Root-NFS. To be frank, I was pretty desperate at that point. Then, a kind soul sent me an email with a kernel containing an integral initrd that worked. So, I knew it was possible and that inspired me to run further trials.

Based on work by chris007, I already had a 2.6.31 kernel compiled and running on the N2200. Soon, I found that I could hard-code the Root-NFS kernel command line parameters into that kernel and, unlike with 2.6.18, it worked!

So, why not try an even more recent kernel? Here we go:

Procedure

• Get vanilla 3.1.10 kernel from http://kernel.org/pub/
• Unpack it in /usr/src/linux-3.1.10
• Create standard symlink: "cd /usr/src && ln -si linux-3.1.10 linux"
• Patch the kernel:

1st patch:

This patch is critical - without it, the kernel will not boot. Comment out the following while loop:

arch/x86/kernel/rtc.c:
/*
* If UIP is clear, then we have >= 244 microseconds before
* RTC registers will be updated.  Spec sheet says that this
* is the reliable way to read RTC - registers. If UIP is set
* then the register access might be invalid.
*/
while ((CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))
cpu_relax();

2nd patch:

This one is not critical, but it corrects a usability issue.

Edit drivers/video/geode/gx1fb_core.c

Look for and change
 static char mode_option[32] = "640x480-16@60";
to
 static char mode_option[32] = "1024x768-16@60";

3rd patch:

This patch is not useful for Root-NFS, but it's a quick-and-dirty way to have your root filesystem on the CF card. Another option would be to pass a hard-coded kernel command-line parameter (see below).

arch/x86/kernel/setup.c

replace
ROOT_DEV = old_decode_dev(boot_params.hdr.root_dev);

by

ROOT_DEV = Root_SDA1;

• Get proper config file: http://smithfarm-thebrain.blogspot.com/2012/01/my-kernel-config-for-linux-3110-on-ibm.html
• Put the config file in /usr/src/linux/.config
• Run "make menuconfig", under ". . ." edit the hardcoded kernel command line to meet your needs.
• "make bzImage"
• run the patch-kernel script (see below) on the arch/x86/boot/compressed/vmlinux file

Antonio Martins' patch-kernel script - a very nice helper. Here's the entire script:

#!/usr/bin/perl

# This script patches the ELF program-header-count in a compiled Linux Kernel.
# This is needed to enable the kernel to run under IBM Netvista 2200 (8363).
#
# You need Perl to run this.
# usage: ./patch-kernel vmlinux
#
# Antonio Cardoso Martins (digiplan.pt@gmail.com)
#
# Version 2008090701
#

# use strict;
# use warnings;

open (FH, "+<$ARGV[0]") or die "Couldn't open $ARGV[0] file for writing: $!";
binmode (FH);

seek(FH, 0x2c, 0) or die "Died seeking: $!";
read(FH, my $value, 1) == 1 or die "died reading: $!";
print "ELF program-header-count (offset 0x2c) of $ARGV[0]\n";
print "Before patching was: " . unpack('C', $value) . "\n";

seek(FH, -1, 1) or die "Died seeking: $!";
print FH pack('C', 1);
print "The value now is:    1\n";

close FH or die "Died closing: $!"; 

The resulting file is your new kernel.

• try booting the N2200 with the new kernel

Result: The kernel boots fine. If I use /bin/sh instead of /sbin/init, it works fine. But if I let it boot into the full Debian system, it segfaults as soon as I run bash. Here's the exact (more-or-less) error message:

-bash: /usr/bin/id: cannot execute binary file
Inconsistency detected by ld.so: dl-fini.c: 197: _dl_fini: Assertion `ns != 0 || i == nloaded' failed!
bash[1388]: segfault at 4 ip . . . etc. etc.
-bash: [: : integer expression expected