Support generating a stub initrd

As part of the rootfs building process, also generate an initrd template
that can be combined with a modular kernel (like GKI) in order to boot
the root filesystem.

Change-Id: I31618ef1ad076a4950555a1f2cc96913e5c807d7

4 files changed, 69 insertions, 9 deletions

diff --git a/net/test/build_rootfs.sh b/net/test/build_rootfs.sh
index 3b7233f..6e216a8 100755
--- a/net/test/build_rootfs.sh
+++ b/net/test/build_rootfs.sh
@@ -29,7 +29,7 @@ export LC_ALL=C
 
 usage() {
   echo -n "usage: $0 [-h] [-s bullseye] [-a i386|amd64|armhf|arm64] "
-  echo "[-m http://mirror/debian] [-n net_test.rootfs.$(date +%Y%m%d)]"
+  echo "[-m http://mirror/debian] [-n rootfs] [-r initrd]"
   exit 1
 }
 
@@ -37,7 +37,10 @@ mirror=http://ftp.debian.org/debian
 suite=bullseye
 arch=amd64
 
-while getopts ":hs:a:m:n:" opt; do
+ramdisk=
+rootfs=
+
+while getopts ":hs:a:m:n:r:" opt; do
   case "${opt}" in
     h)
       usage
@@ -64,7 +67,10 @@ while getopts ":hs:a:m:n:" opt; do
       mirror="${OPTARG}"
       ;;
     n)
-      name="${OPTARG}"
+      rootfs="${OPTARG}"
+      ;;
+    r)
+      ramdisk="${OPTARG}"
       ;;
     \?)
       echo "Invalid option: ${OPTARG}" >&2
@@ -77,13 +83,20 @@ while getopts ":hs:a:m:n:" opt; do
   esac
 done
 
-if [[ -z "${name}" ]]; then
-  name="net_test.rootfs.${arch}.${suite}.$(date +%Y%m%d)"
+if [[ -z "${rootfs}" ]]; then
+  rootfs="rootfs.${arch}.${suite}.$(date +%Y%m%d)"
+fi
+rootfs=$(realpath "${rootfs}")
+
+if [[ -z "${ramdisk}" ]]; then
+  ramdisk="initrd.${arch}.${suite}.$(date +%Y%m%d)"
 fi
+ramdisk=$(realpath "${ramdisk}")
 
 # Sometimes it isn't obvious when the script fails
 failure() {
   echo "Filesystem generation process failed." >&2
+  rm -f "${rootfs}" "${ramdisk}"
 }
 trap failure ERR
 
@@ -118,6 +131,7 @@ sudo mkdir host
 
 sudo chroot . root/stage2.sh
 sudo chroot . root/${suite}.sh
+raw_initrd="${PWD}"/boot/initrd.img
 
 # Workarounds for bugs in the debootstrap suite scripts
 for mount in $(cat /proc/mounts | cut -d' ' -f2 | grep -e "^${workdir}"); do
@@ -125,7 +139,36 @@ for mount in $(cat /proc/mounts | cut -d' ' -f2 | grep -e "^${workdir}"); do
   sudo umount "${mount}"
 done
 
+# Leave the workdir, to process the initrd
+cd -
+
+# New workdir for the initrd extraction
+workdir="${tmpdir}/initrd"
+mkdir "${workdir}"
+chmod 0755 "${workdir}"
+sudo chown root:root "${workdir}"
+
+# Change into workdir to repack initramfs
+cd "${workdir}"
+
+# Process the initrd to remove kernel-specific metadata
+lz4 -lcd "${raw_initrd}" | sudo cpio -idum
+sudo rm -f "${raw_initrd}"
+sudo rm -rf usr/lib/modules
+sudo mkdir -p usr/lib/modules
+
+# Debian symlinks /usr/lib to /lib, but we'd prefer the other way around
+# so that it more closely matches what happens in Android initramfs images.
+# This enables 'cat ramdiskA.img ramdiskB.img >ramdiskC.img' to "just work".
+sudo rm -f lib
+sudo mv usr/lib lib
+sudo ln -s /lib usr/lib
+
+# Repack the ramdisk to the final output
+find * | sudo cpio -H newc -o --quiet | lz4 -lc9 >"${ramdisk}"
+
 # Leave the workdir, to build the filesystem
+workdir="${tmpdir}/_"
 cd -
 
 # For the final image mount
@@ -137,11 +180,11 @@ mount_remove() {
 trap mount_remove EXIT
 
 # Create a 1G empty ext3 filesystem
-truncate -s 1G "${name}"
-mke2fs -F -t ext3 -L ROOT "${name}"
+truncate -s 1G "${rootfs}"
+mke2fs -F -t ext3 -L ROOT "${rootfs}"
 
 # Mount the new filesystem locally
-sudo mount -o loop -t ext3 "${name}" "${mount}"
+sudo mount -o loop -t ext3 "${rootfs}" "${mount}"
 image_unmount() {
   sudo umount "${mount}"
   mount_remove
@@ -155,4 +198,5 @@ sudo cp -a "${workdir}"/* "${mount}"
 sudo dd if=/dev/zero of="${mount}/sparse" bs=1M 2>/dev/null || true
 sudo rm -f "${mount}/sparse"
 
-echo "Debian ${suite} for ${arch} filesystem generated at '${name}'."
+echo "Debian ${suite} for ${arch} filesystem generated at '${rootfs}'."
+echo "Initial ramdisk generated at '${ramdisk}'."
diff --git a/net/test/rootfs/bullseye.list b/net/test/rootfs/bullseye.list
index f6ab2a2..e908a11 100644
--- a/net/test/rootfs/bullseye.list
+++ b/net/test/rootfs/bullseye.list
@@ -3,9 +3,11 @@ apt-utils
 bash-completion
 bsdmainutils
 ca-certificates
+e2fsprogs
 file
 gpgv
 ifupdown
+initramfs-tools
 insserv
 iputils-ping
 iptables
@@ -13,6 +15,7 @@ isc-dhcp-client
 less
 libnetfilter-conntrack3
 libnfnetlink0
+lz4
 mime-support
 netbase
 netcat-openbsd
diff --git a/net/test/rootfs/common.sh b/net/test/rootfs/common.sh
index 17afbfe..35e5745 100644
--- a/net/test/rootfs/common.sh
+++ b/net/test/rootfs/common.sh
@@ -67,6 +67,11 @@ cleanup() {
   mkdir -p /var/lib/systemd/{coredump,linger,rfkill,timesync}
   chown systemd-timesync:systemd-timesync /var/lib/systemd/timesync
 
+  # If embedding isn't enabled, remove the embedded modules and initrd and
+  # uninstall the tools to regenerate the initrd, as they're unlikely to
+  # ever be used
+  apt-get purge -y initramfs-tools initramfs-tools-core klibc-utils kmod
+
   # Miscellaneous cleanup
   rm -rf /var/lib/apt/lists/* || true
   rm -f /root/* || true
diff --git a/net/test/rootfs/stage2.sh b/net/test/rootfs/stage2.sh
index bb35b78..26be79e 100755
--- a/net/test/rootfs/stage2.sh
+++ b/net/test/rootfs/stage2.sh
@@ -53,3 +53,11 @@ mkdir -p /var/empty
 rm -rf /root/stage2.sh /tmp/*
 find /var/log -type f -exec rm -f '{}' ';'
 find /var/tmp -type f -exec rm -f '{}' ';'
+
+# Create an empty initramfs to be combined with modules later
+sed -i 's,^COMPRESS=gzip,COMPRESS=lz4,' /etc/initramfs-tools/initramfs.conf
+mkdir -p /lib/modules/0.0
+depmod -a 0.0
+update-initramfs -c -k 0.0
+mv /boot/initrd.img-0.0 /boot/initrd.img
+rm -rf /lib/modules/0.0