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Optional Root filesystem build and use instructions
===================================================
A Introduction
This note describes ways to build Linux user-land
filesystems of varying complexity for use with the
virtualizer. Note that there are several ways to create
filesystems and this note doesn't cover all possibilities.
The default virtualizer release contains an empty filesystem
stub located at:
arm-virtualizer-v2_1-171111/bootwrapper/payload/fsimg
A build using this stub doesn't contain a functional
filesytem that the Linux kernel image can use. fsimg can be
replaced with a suitable filesystem image but with the
following constraints:
1. Compressed or uncompressed cpio archives are supported.
2. The image size is limited to ~200 MB.
The size restriction implies that only very 'lean'
filesystems such as busybox <http://www.busybox.net/> may be
used. While busybox presents a minimal but robust command
line environment, quite often a more conventional desktop
like environment with window management on top of an X
server is required in order to run web browsers etc.
In this note, we illustrate a method to use a larger (~2GB) filesystem image
that can be used with the ARM FastModels MMC emulation. Note that the MMC
emulations only supports images that are just under 2GB in size.
Note that if the MMC route is used, the bootwrapper/payload/fsimg filesystem
image will be suppressed and ignored.
Locating a root filesystem on the MMC emulation allows the Linux kernel to
access and use this filesystem. This is facilitated by indicating the
filesystem location to the kernel via the kernel command-line arguments by
appending 'root=/dev/mmcblk0' (for a single partition MMC image) to the
argument list.
Note that when using this technique, the fsimg file is ignored.
B Building and installing a Linux kernel
A suitable Linux kernel image for use with the virtualizer
can be built as follows:
$ tar -jxf arm-virtualizer-v2_1-171111.tar.bz2
$ cd arm-virtualizer-v2_1-171111/bootwrapper
$ make clean
$ pushd /tmp
$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/maz/ael-kernel.git ael-kernel.git
$ cd ael-kernel.git
$ git checkout -b ael-11.06 origin/ael-11.06
$ yes | make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- vexpress-new_defconfig
$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- -j4
$ popd
$ cp $OLDPWD/arch/arm/boot/Image payload/kernel
Note that the using the vexpress-new_defconfig configuration
ensures that the kernel is built with MMC support.
C Building a suitable root filesystem
A suitable root filesystem can be built using Ubuntu Linux's rootstock utility
<https://wiki.ubuntu.com/ARM/RootfsFromScratch> as follows:
$ sudo apt-get install rootstock
$ sudo rootstock --fqdn ubuntu --login ubuntu --password ubuntu --imagesize 2040M --seed lxde,gdm --notarball
$ mv qemu-armel-*.img mmc.img
Note that the complete filesystem build will take ~30
minutes. On boot, the username and password is 'ubuntu'.
The rootstock invocation above will produce a rootfilesystem containing an
LXDE desktop <http://lxde.org/> that has a firefox browser.
D Modifying the kernel command line to support the MMC image.
The virtualizer build system and the mxscripts that are used for launching
the ARM FastModel require modifications to support the MMC image.
The build system modification is to change the Linux kernel command line
arguments to make the kernel aware of the location of the root filesystem.
The command line should contain the string 'root=/dev/mmcblk0'.
To make this modification, edit the file bootwrapper/Makefile and change the
BOOTARGS specification on line 42 from:
BOOTARGS=mem=255M console=ttyAMA0,115200 migration_cost=500
cachepolicy=writealloc
to
BOOTARGS=root=/dev/mmcblk0 mem=255M console=ttyAMA0,115200
migration_cost=500 cachepolicy=writealloc
The ARM FastModel mxscript modification is to get the FastModel to use the
mmc.img file created in step C above with the MMC emulation.
To make this modification uncomment the 'string mmcimage=' line (line 42)
and provide the complete path to the mmc.img file generated in step C above.
E Building the virtualizer
$ cd bootwrapper
$ make clean && make
F Launching the ARM FastModel
$ modeldebugger -s big-little-MP<x>.mxscript
.. where x is 1 or 4 as the case may be (MP1 build or MP4
build).
G Known limitations
Use of a comprehensive root filesystem as opposed to busybox
is known to be unstable on the current ARM FastModel release (Release
6.2 Beta). Subsequent model releases shall contain appropriate fixes as
required).
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