Add support for Ubuntu Base.

Install the base system from a downloadable image, then patch it with
the PACKAGES we need. This method produces a much smaller image than
with debootstrap, and the building process completes much more quickly.

The process also does not require root (with some caveats). The debian
program 'fakeroot' replaces all uses of 'sudo' to ensure that the user
and group of files in the final tarball remains the same.

Signed-off-by: Alistair Strachan <astrachan@google.com>

Author: Alistair Strachan

README.md

@@ -34,7 +34,7 @@ at least 2 GB free space in the data partition.
 
 Host:
 A machine running recent Ubuntu or Debian, with 4GB of memory and 4GB free space.
-Host needs debootstrap and qemu-user-static packages. To install these,
+Host needs debootstrap, fakeroot and qemu-user-static packages. To install these,
 run `sudo apt-get install debootstrap fakeroot qemu-user-static`.
 Other distributions may work but they are not tested.
 

androdeb

@@ -63,6 +63,7 @@ esac
 case $DISTRO in
     buster) ;;
     bionic)
+        DISTRO_VERSION=18.04
         if [ "$ARCH" == "i386" -o "$ARCH" == "amd64" ]; then
             MIRROR=http://archive.ubuntu.com/ubuntu/
         else
@@ -182,7 +183,7 @@ fi
 PACKAGES+="$DEFAULT_PACKAGES"
 echo "Using temporary directory: $TDIR"
 
-$spath/buildstrap $ARCH $DISTRO $TDIR $OUT_TMP "$PACKAGES" "$INSTALL_BCC" $MIRROR
+$spath/buildstrap $ARCH $DISTRO $TDIR $OUT_TMP "$PACKAGES" "$INSTALL_BCC" $MIRROR "$DISTRO_VERSION"
 
 # Push tar to device and start unpack
 $ADB shell mkdir -p /data/androdeb/

buildstrap

@@ -11,18 +11,42 @@ OUT_TMP=$4
 PACKAGES=$5
 INSTALL_BCC=$6
 MIRROR=$7
+DISTRO_VERSION=$8
 
-root=sudo
+if [[ ! -z $DISTRO_VERSION ]]; then
+    # Assume non-empty DISTRO_VERSION is Ubuntu; see if there's a base image..
+    echo "Checking for Ubuntu Base image from the web..."; echo ""
+    if [ ! -f $TDIR/ubuntu-base-$DISTRO_VERSION-base-$ARCH.tar.gz ]; then
+        curl -L http://cdimage.ubuntu.com/ubuntu-base/releases/$DISTRO_VERSION/release/ubuntu-base-$DISTRO_VERSION-base-$ARCH.tar.gz \
+            --output $TDIR/ubuntu-base-$DISTRO_VERSION-base-$ARCH.tar.gz; fi
+    if [ -f $TDIR/ubuntu-base-$DISTRO_VERSION-base-$ARCH.tar.gz ]; then
+        time tar -C $OUT_TMP --exclude=dev -xf $TDIR/ubuntu-base-$DISTRO_VERSION-base-$ARCH.tar.gz;
+        mkdir $OUT_TMP/dev; fi; fi
 
-if [ $EUID -ne 0 ]; then echo "The next stage runs as sudo, please enter password if asked."; fi
+if [ ! -f $OUT_TMP/etc/debian_version ]; then
+    root=sudo
 
-# It's easier to just really be root for debootstrap
-time $root qemu-debootstrap --arch $ARCH --include="$(make_csv "$PACKAGES")" \
-	$DISTRO $OUT_TMP $MIRROR
+    if [ $EUID -ne 0 ]; then echo "The next stage runs as sudo, please enter password if asked."; fi
 
-# Some reason debootstrap leaves these mounted
-$root umount $OUT_TMP/proc/sys/fs/binfmt_misc || true
-$root umount $OUT_TMP/proc || true
+    # It's easier to just really be root for debootstrap
+    time $root qemu-debootstrap --arch $ARCH --include="$(make_csv "$PACKAGES")" \
+        $DISTRO $OUT_TMP $MIRROR
+
+    # Some reason debootstrap leaves these mounted
+    $root umount $OUT_TMP/proc/sys/fs/binfmt_misc || true
+    $root umount $OUT_TMP/proc || true
+else
+    root=fakeroot
+
+    # Avoid 'apt-get install' because this requires chroot, which requires root
+    # FIXME: Note, this only works if PACKAGES fully describes the dependency
+    #        chain, and it also only if the postinst scripts for the packages
+    #        are not critical.
+    for PACKAGE in $PACKAGES; do
+        FILE=`cat $OUT_TMP/var/lib/apt/lists/*Packages | grep -e "^Filename:.*/${PACKAGE}_" | cut -d' ' -f2`
+        echo "Fetching ${MIRROR}${FILE}..."; echo ""
+        curl -L ${MIRROR}${FILE} --output $TDIR/`basename $FILE`
+        $root dpkg-deb -x $TDIR/`basename $FILE` $OUT_TMP; done; fi
 
 # Make bash the default shell
 $root ln -sf /bin/bash $OUT_TMP/bin/sh || true