[Galaxy S I9000 Android Development] appagom:
First this diff is from a z4modded stock SL28 image to the custom kernel image. It's not against stock. So it includes tegrak files and scripts I changed. Also note the -N option. It pretends like files that don't exist do.. Any binary files that "differ" are actually added from tegrak.

diff -rbpN z4mod_sl28/initramfs/init.rc z4grak-construction-sl28/initramfs/init.rc
*** z4mod_sl28/initramfs/init.rc	2011-01-13 02:20:12.000000000 -0500
--- z4grak-construction-sl28/initramfs/init.rc	2011-01-11 07:43:34.000000000 -0500
*************** loglevel 3
*** 58,63 ****
--- 58,72 ----
mount j4fs /dev/block/stl6 /mnt/.lfs
insmod /lib/modules/param.ko

+ #ext4 modules by woo
+ insmod /tegrak/lib/modules/mbcache.ko
+ insmod /tegrak/lib/modules/jbd2.ko
+ insmod /tegrak/lib/modules/ext4.ko
+
+ # tegrak system lagfix by woo
+ #
+ insmod /tegrak/lib/modules/tegrak_module.ko
+
# Backwards Compat - XXX: Going away in G*
symlink /mnt/sdcard /sdcard

*************** service vt /system/bin/vtserver
*** 728,734 ****
#user system
#group system

-
service dumpstate /system/bin/dumpstate -s
socket dumpstate stream 0660 shell log
disabled
--- 737,742 ----
*************** service dumpstate /system/bin/dumpstate
*** 739,747 ****
# oneshot

-
# Added by z4mod
service z4postinit /init
oneshot

--- 747,761 ----
# oneshot

# Added by z4mod
service z4postinit /init
oneshot

+ #install root ingore the mount type, it doesn't matter
+ # syntax looks a little strange to me.. we'll see if it works
+ mount rfs /dev/block/stl9 /system rw remount
+ cat /sbin/su > /system/bin/su
+ chown root /system/bin/su
+ chmod 4755 /system/bin/su
+ mount rfs /dev/block/stl9 /system ro remount

\ No newline at end of file
diff -rbpN z4mod_sl28/initramfs/lpm.rc z4grak-construction-sl28/initramfs/lpm.rc
*** z4mod_sl28/initramfs/lpm.rc	2011-01-13 02:20:12.000000000 -0500
--- z4grak-construction-sl28/initramfs/lpm.rc	2011-01-11 06:37:28.000000000 -0500
*************** on init
*** 16,21 ****
--- 16,26 ----
insmod /lib/modules/param.ko
insmod /lib/modules/vibrator.ko

+ #ext4 modules by woo
+	insmod /tegrak/lib/modules/mbcache.ko
+	insmod /tegrak/lib/modules/jbd2.ko
+	insmod /tegrak/lib/modules/ext4.ko
+
mount rfs /dev/block/stl9 /system check=no
mount rfs /dev/block/mmcblk0p2 /data nosuid nodev check=no

Binary files z4mod_sl28/initramfs/sbin/sslvpn and z4grak-construction-sl28/initramfs/sbin/sslvpn differ
Binary files z4mod_sl28/initramfs/tegrak/bin/mkfs.ext4 and z4grak-construction-sl28/initramfs/tegrak/bin/mkfs.ext4 differ
Binary files z4mod_sl28/initramfs/tegrak/bin/tune2fs and z4grak-construction-sl28/initramfs/tegrak/bin/tune2fs differ
Binary files z4mod_sl28/initramfs/tegrak/lib/modules/ext4.ko and z4grak-construction-sl28/initramfs/tegrak/lib/modules/ext4.ko differ
Binary files z4mod_sl28/initramfs/tegrak/lib/modules/jbd2.ko and z4grak-construction-sl28/initramfs/tegrak/lib/modules/jbd2.ko differ
Binary files z4mod_sl28/initramfs/tegrak/lib/modules/mbcache.ko and z4grak-construction-sl28/initramfs/tegrak/lib/modules/mbcache.ko differ
Binary files z4mod_sl28/initramfs/tegrak/lib/modules/tegrak_module.ko and z4grak-construction-sl28/initramfs/tegrak/lib/modules/tegrak_module.ko differ

I'm a bit confused about sslvpn It's in my SL28 , it's not in my z4moded SL28. everything else diff as expected. Maybe I just lost it, maybe z4mod removed it. It's a small unimportant mystery.

BTW it looks like what I believe are the recovery keys have changed from SK22 to SL28, so maybe using the wrong kernel breaks something.

and my slightly modified version of the extraction script with commented lines to deal with lzma.

it's much faster (well.. why not), and it handles direcories a little better. It need a "/" somewhere in the file name though so use "./zImage".

#!/bin/bash

#MUCH faster than dd bs=1 skip=blah
#
# syntas is fastdd file skip <length_in_bytes_optional>
# skip is NOT optional and should be set to 0 read from begining.
#
fastdd () {
#dd with a skip is crazy slower cause it forces bs=1
#credit goes to somebody on the internet.
local bs=1024
local file=$1
local skip=$2
local count=$3

(
dd bs=1 skip=$skip count=0 2>/dev/null
if [[ "$count" != "" ]]; then
dd bs=$bs count=$(($count / $bs))
dd bs=$(($count % $bs)) count=1
else
dd bs=1024 2> /dev/null
fi
) < "$file"
}

zImage=$1
basedir=${1%/*}
echo working directory $basedir
mkdir $basedir/initramfs
outdir=$basedir/initramfs/
#========================================================
# find start of gziped kernel object in the zImage file:
#========================================================
pos=`grep -P -a -b -m 1 --only-matching $'\x1F\x8B\x08' $zImage | cut -f 1 -d :`
echo "-I- Extracting kernel image from $zImage (start = $pos)"
echo
echo "*** Start of compressed kernel image:" $pos
#========================================================================
# the cpio archive might be gzipped too, so two gunzips could be needed:
#========================================================================
fastdd $zImage $pos | gunzip > /tmp/kernel.img
pos=`grep -P -a -b -m 1 --only-matching $'\x1F\x8B\x08' /tmp/kernel.img | cut -f 1 -d :`
#
# Use next one for tegrak secuere 11 SL28
# It's an lzma header
# It's found by looking for 5D 00 in the exact same place as cpio (070701) is found in stock.
# The long string of FF's is the real give away since 5D 00 is too vague.
# pos=`grep -P -a -b -m 1 --only-matching '\x{5D}\x{00}\x..\x{FF}\x{FF}\x{FF}\x{FF}\x{FF}\x{FF}' /tmp/kernel.img| cut -f 1 -d :`
echo
echo "*** gzip position in kernel.img :" $pos "(start of gzipped cpio)"
#===========================================================================
# find start and end of the "cpio" initramfs image inside the kernel object:
# ASCII cpio header starts with '070701'
# The end of the cpio archive is marked with an empty file named TRAILER!!!
#===========================================================================
if [ ! $pos = "" ]; then
echo "-I- Extracting compressed cpio image from kernel image (start = $pos)"
# use either one of the next two lines for gzip
# dd if=/tmp/kernel.img bs=1 skip=$pos | gunzip > /tmp/cpio.img
fastdd /tmp/kernel.img $pos |gunzip > /tmp/cpio.img
# comment above and uncomment one of next two lines for lzma, if decompressing tegrak image.
# dd if=/tmp/kernel.img bs=1 skip=$pos | unlzma > /tmp/cpio.img
# fastdd /tmp/kernel.img $pos | unlzma > /tmp/cpio.img
start=`grep -a -b -m 1 --only-matching '070701' /tmp/cpio.img | head -1 | cut -f 1 -d :`
end=`grep -a -b -m 1 --only-matching 'TRAILER!!!' /tmp/cpio.img | head -1 | cut -f 1 -d :`
inputfile=/tmp/cpio.img
else
echo "-I- Already uncompressed cpio.img, not decompressing"
start=`grep -a -b -m 1 --only-matching '070701' /tmp/kernel.img | head -1 | cut -f 1 -d :`
echo start $start
end=`grep -a -b -m 1 --only-matching 'TRAILER!!!' /tmp/kernel.img | head -1 | cut -f 1 -d :`
echo end $end
inputfile=/tmp/kernel.img
fi

end=$((end + 10))
count=$((end - start))
if (($count < 0)); then
echo "-E- Couldn't match start/end of the initramfs image."
exit
fi
echo "-I- Extracting initramfs image from $inputfile (start = $start, end = $end)"
echo inputfile: $inputfile
echo start $start
echo count $count
echo outdir $outdir
# dd if=$inputfile bs=1 skip=$start count=$count > $outdir/initramfs.cpio
fastdd $inputfile $start $count > $basedir/initramfs.cpio
cd $basedir
basedir=`pwd`
cd $outdir; cpio -v -i --no-absolute-filenames < $basedir/initramfs.cpio
cp /tmp/kernel.img $basedir/

More to come.