Patching Linux Kernel 5.5.7 to Add Support for AUFS Filesystem

Subject of Hint: Patching Linux Kernel 5.5.7 to Add Support for AUFS Filesystem

ORIGINAL AUTHOR: JIMMY ANDERSON
ORIGINAL DATE: 2013-01-20

EDITED BY: TURRITOPSIS DOHRNII TEO EN MING, SINGAPORE
EDIT DATE: 15 MAR 2020 SUNDAY

MANDATORY PREREQUISITES
=======================

You *MUST* follow the guide/hint here first (COMPULSORY):

http://lists.linuxfromscratch.org/pipermail/hints/2020-March/003334.html

HINT
====

To obtain the aufs5 kernel patches, do the following:
 
$ sudo apt install git

#------------ Cut and Paste start
cd $LFS/sources
git clone git://github.com/sfjro/aufs5-standalone.git \
aufs5-standalone.git
cd aufs5-standalone.git
git checkout -b origin/aufs5.5
cp aufs5-*.patch ..
rm -f include/uapi/linux/Kbuild
tar cvfz $LFS/sources/aufs5.tar.gz Documentation fs include
cd ..
rm -rf aufs5-standalone.git
#------------ Cut and Paste end

Rebuilding your kernel
======================

   Follow the instructions in the LFS/BLFS book and build your LFS system
as you normally would except that during the kernel build, after unpacking
the source and cd'ing into the linux directory, you apply either
the unionfs or the aufs patches. 


To apply aufs patches:
#------------ Cut and Paste start
cat ../aufs5-base.patch  |patch -Np1
cat ../aufs5-kbuild.patch  |patch -Np1
cat ../aufs5-mmap.patch  |patch -Np1
cat ../aufs5-standalone.patch  |patch -Np1
tar xvf ../aufs5.tar.gz
#------------ Cut and Paste end

When you configure the kernel, make sure the following are enabled
as builtins (not as modules):

   SQUASHFS support (and support for SQUASHFS XZ compressed file systems).
   UNIONFS or AUFS support (CONFIG_AUFS_FS=y)
   CDROM support (ISO9660).
   DEVTMPFS support.

Then build and install as normal:
#------------ Cut and Paste start
make
make modules_install
cp arch/x86/boot/bzImage /boot/vmlinuz-5.5.7-turritopsis.dohrnii.teo.en.ming
cp .config /boot/config-5.5.7            ***VERY VERY IMPORTANT TO HAVE A BACKUP OF YOUR KERNEL CONFIGURATION***
#------------ Cut and Paste end

Start compiling Linux Kernel 5.5.7: 8.20 PM
End compiling Linux Kernel 5.5.7: 8.39 PM
Duration: 19 mins on an AMD Ryzen 3 3200G processor with Radeon Vega 8 graphics,
Gigabyte B450M DS3H motherboard with BIOS version F41, and 32 GB Transcend DDR4-2666 RAM.

Remake a squashed version of your LFS.
======================================

Exit the chroot and unmount any filesystems that are associated with
the $LFS directory.   At this point, it is a good idea to do a system
shutdown and restart to ensure that the LFS directory is unused and
in a quiescent state.   Make sure LFS is set again after the reboot.

#------------ Cut and Paste start
# Set LFS value as needed...
export LFS=/mnt/lfs
cd /home/teo-en-ming
echo $LFS
rm -f root.sfs
sudo mv /mnt/lfs/sources/ /home/teo-en-ming/
sudo mksquashfs $LFS root.sfs -comp xz
#------------ Cut and Paste end

(omit the -comp xz if your squashfs tools don't support xz compression).

MODIFY THE LIVE CD/DVD IMAGE
============================

cd /home/teo-en-ming/Downloads
cp -v /home/teo-en-ming/root.sfs live/boot/$(uname -m)
cp -v $LFS/boot/vmlinuz-5.5.7-turritopsis.dohrnii.teo.en.ming live/boot/$(uname -m)/vmlinuz

Create the live CD/DVD iso image using whatever iso creation tool you
have.   In this example, it is 'genisoimage':

#------------ Cut and Paste start
genisoimage -o teo-en-ming-linux-2020.03-final-live-cd-dvd.iso     \
         -b boot/isolinux/isolinux.bin \
         -c boot.cat                   \
         -no-emul-boot                 \
         -boot-load-size 4             \
         -boot-info-table              \
         -joliet -l -R                 \
         live

rm -rf live           ### OPTIONAL
#------------ Cut and Paste end

LIVE CD/DVD BOOTS WITH KERNEL PANIC
===================================

After patching Linux Kernel 5.5.7 to add support for AUFS filesystem, the generated Live CD/DVD still boots
with a kernel panic.

The error message is as follows:

"end Kernel panic - not syncing: Attempted to kill init! exit code=0x00000200"

After hours of troubleshooting, I think that the problem may lie with the initramfs (busybox based ramdisk) or the following
script init.sh. The following script init.sh may need to be modified to allow the Live CD/DVD to boot successfully.

I hope that the LFS community would be able to spend some time looking at init.sh and modify it so that the resultant Live CD/DVD
will be able to boot successfully.

I would like to thank all of you in advance.

The original script init.sh (8 years ago) is reproduced as follows:

ADDENDUM: v Cut and save the remainder of this file as $LFS/sources/init.sh v
#!/bin/busybox sh
#
# This file is a modified version of:
#
# Initramfs boot script 1.3.1 (2012-02-09)
# Copyright (c) 2010-2012   Marcel van den Boer
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to
# deal in the Software without restriction, including without limitation the
# rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
# sell copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
# IN THE SOFTWARE.

# FS layout at the start of this script:
# - /boot/id_label
# - /bin/busybox
# - /dev/console (created by kernel)
# - /init (this file)

set -e

ARCH="<ARCH>"

###########################################
copyBindMount() { # COPY/BIND LIVECD MODE #
###########################################

# This function bind-mounts directories which are designed to be capable of
# read-only access and copies the remaining directories to a tmpfs.
#
# The downside of this method is that the resulting root filesystem is not
# fully writable. So, for example, installation of new programs will not be
# possible.
#
# However, this function can be used without any modification to the kernel and
# is therefore perfect for use as a fallback if other options are not available.

# Mount a tmpfs where the new rootfs will be.
mount -t tmpfs tmpfs ${ROOT} # Allows remounting root in the bootscripts

# Bind mount read-only filesystems, copy the rest
cd /mnt/system
for dir in $(ls -1); do
    case ${dir} in
        lost+found)
            ;;
        bin | boot | lib | opt | sbin | usr)
            mkdir ${ROOT}/${dir}
            mount --bind ${dir} ${ROOT}/${dir}
            ;;
        *)
            cp -R ${dir} ${ROOT}
            ;;
    esac
done
cd /

##############################################
}; unionMount() { # UNIONFS/AUFS LIVECD MODE #
##############################################

# A union mount takes one or more directories and combines them transparantly
# in a third. This function creates a writable directory in memory (tmpfs) and
# uses it to overlay the read-only system image, resulting in a fully writable
# root file system.
#
# The only downside to this method is that it requires a union type filesystem
# in the kernel, which can only be accomplished by patching the kernel as there
# is no such feature in a vanilla kernel.

mkdir -p /mnt/writable
mount -t tmpfs -o rw tmpfs /mnt/writable

UNIONFSOPT="/mnt/writable=rw:/mnt/system=ro"
AUFSOPT="/mnt/writable=rw:/mnt/system=ro"
mount -t unionfs -o dirs=${UNIONFSOPT} unionfs ${ROOT} 2> /dev/null || \
mount -t aufs -o br=${AUFSOPT} none ${ROOT} 2> /dev/null || \
{
    # If UnionFS fails, fall back to copy/bind mounting
    copyBindMount
}

######################
} # END OF FUNCTIONS #
######################

# Make required applets easier to access
for applet in cat chmod cp cut grep ls mkdir mknod mount umount switch_root \
    rm mv vi cpio tar mke2fs sync fdisk dd ; do
    /bin/busybox ln /bin/busybox /bin/${applet}
done

# Clear the screen
#clear # Don't! This will clear the Linux boot logo when using a framebuffer.
       # If you want to clear the screen on boot add the "clear" command to
       # '/usr/share/live/sec_init.sh' in the system image.

# Create device nodes required to run this script
# Note: /dev/console will already be available in the ramfs
mknod /dev/null c  1  3

mknod /dev/scd0 b 11  0  # +--------
mknod /dev/scd1 b 11  1  # |
mknod /dev/scd2 b 11  2  # |
mknod /dev/scd3 b 11  3  # |
                         # |
mknod /dev/hdc  b 22  0  # |
                         # |
mknod /dev/sda  b  8  0  # |
mknod /dev/sda1 b  8  1  # |
mknod /dev/sda2 b  8  2  # |
mknod /dev/sda3 b  8  3  # |
mknod /dev/sda4 b  8  4  # |
                         # |
mknod /dev/sdb  b  8 16  # |    <----
mknod /dev/sdb1 b  8 17  # |        Devices which could be or contain the
mknod /dev/sdb2 b  8 18  # |        boot medium...
mknod /dev/sdb3 b  8 19  # |
mknod /dev/sdb4 b  8 20  # |
                         # |
mknod /dev/sdc  b  8 32  # |
mknod /dev/sdc1 b  8 33  # |
mknod /dev/sdc2 b  8 34  # |
mknod /dev/sdc3 b  8 35  # |
mknod /dev/sdc4 b  8 36  # |
                         # |
mknod /dev/sdd  b  8 48  # |
mknod /dev/sdd1 b  8 49  # |
mknod /dev/sdd2 b  8 50  # |
mknod /dev/sdd3 b  8 51  # |
mknod /dev/sdd4 b  8 52  # +--------

# Create mount points for filesystems
mkdir -p /mnt/medium
mkdir -p /mnt/system
mkdir -p /mnt/rootfs

# Mount the /proc filesystem (enables filesystem detection for 'mount')
mkdir /proc
mount -t proc proc /proc

# Invoke busybox if requested via the kernel command line.
if [ `grep -c "busybox" /proc/cmdline` -ne "0" ]; then
    echo "Busybox requested";
    busybox sh
fi

# Search for, and mount the boot medium
LABEL="$(cat /boot/id_label)"
for device in $(ls /dev); do
    [ "${device}" == "console" ] && continue
    [ "${device}" == "null"    ] && continue

    mount -o ro /dev/${device} /mnt/medium 2> /dev/null && \
    if [ "$(cat /mnt/medium/boot/${ARCH}/id_label)" != "${LABEL}" ]; then
        umount /mnt/medium
    else
        DEVICE="${device}"
        break
    fi
done

if [ "${DEVICE}" == "" ]; then
    echo "FATAL: Boot medium not found."
    /bin/busybox sh
fi

# Mount the system image
mount -t squashfs -o ro,loop /mnt/medium/boot/${ARCH}/root.sfs /mnt/system || {
    echo "FATAL: Boot medium found, but system image is missing."
    /bin/busybox sh
}

# Define where the new root filesystem will be
ROOT="/mnt/rootfs" # Also needed for /usr/share/live/sec_init.sh

# Run in bootable cd mode if requested via the kernel command line.
if [ `grep -c "bootcd" /proc/cmdline` -ne "0" ]; then
    echo "Bootcd mode (bind mount) requested";
    copyBindMount
else
    # Select LiveCD mode
    unionMount # Might fall back to copyBindMount
fi

# Tell LFS to skip fsck during startup:
> $ROOT/fastboot

# Get rid of / manipulations in mountfs script:
grep -v ' \/ ' $ROOT/etc/rc.d/init.d/mountfs > $ROOT/tmp/mountfs
rm -f $ROOT/etc/rc.d/init.d/mountfs
mv $ROOT/tmp/mountfs $ROOT/etc/rc.d/init.d/mountfs
chmod +x $ROOT/etc/rc.d/init.d/mountfs

# Move current mounts to directories accessible in the new root
cd /mnt
for dir in $(ls -1); do
    if [ "${dir}" != "rootfs" ]; then
        mkdir -p ${ROOT}/mnt/.boot/${dir}
        mount --move /mnt/${dir} ${ROOT}/mnt/.boot/${dir}
    fi
done
cd /

# Run secondary initialization (if the system provides it)
if [ -x ${ROOT}/usr/share/live/sec_init.sh ]; then
    . ${ROOT}/usr/share/live/sec_init.sh
fi

# Clean up
umount /proc

# Switch to the new root and launch INIT!
exec switch_root -c /dev/console ${ROOT} /sbin/init





REFERENCES
==========

[1] https://github.com/teo-en-ming/teo-en-ming-linux/blob/master/Patching%20Linux%20Kernel%205.5.7%20to%20Add%20Support%20for%20AUFS%20Filesystem.txt

[2] http://lists.linuxfromscratch.org/pipermail/hints/2020-March/003335.html

[3] http://lists.linuxfromscratch.org/pipermail/blfs-support/2020-March/081868.html

[4] http://lists.linuxfromscratch.org/pipermail/lfs-support/2020-March/053536.html

[5] http://lists.linuxfromscratch.org/pipermail/lfs-chat/2020-March/029102.html

[6] https://lkml.org/lkml/2020/3/15/219

[7] http://lkml.iu.edu/hypermail/linux/kernel/2003.1/08257.html

[8] https://marc.info/?l=linux-kernel&m=158428878211543&w=2