Meta: Support building images without root permissions

If both the fakeroot and genext2fs tools are installed, mount (and
therefore sudo) is not required. Instead we can set the appropriate file
permissions in the root file system in a fakeroot environment and
then use genext2fs to generate the image.

Meta/build-image-qemu.sh

@@ -7,8 +7,21 @@ die() {
     exit 1
 }
 
+# If both the fakeroot and genext2fs tools are installed, no root permissions
+# are required. If either tool is missing, we have to fall back to mounting
+# the image which does require root.
+
+can_use_fakeroot=0
+if (command -v fakeroot 1> /dev/null) && (command -v genext2fs 1> /dev/null); then
+    can_use_fakeroot=1
+fi
+
 if [ "$(id -u)" != 0 ]; then
-    exec sudo -E -- "$0" "$@" || die "this script needs to run as root"
+    if [ $can_use_fakeroot = 1 ]; then
+	exec fakeroot "$0" "$@" || die "simulating root permissions with fakeroot failed"
+    else
+	exec sudo -E -- "$0" "$@" || die "this script needs to run as root"
+    fi
 else
     : "${SUDO_UID:=0}" "${SUDO_GID:=0}"
 fi