✨ Add support for multiple overlay devices

Signed-off-by: Daniel Ruthardt <druthardt@linuxfoundation.org>

Author: Daniel Ruthardt

overlayroot/etc/overlayroot.conf

@@ -17,13 +17,13 @@
 #     overlayroot=tmpfs
 #     overlayroot=tmpfs:swap=1
 #
-#  * overlayroot=DEVICE or overlayroot=device:PARAMETERS
-#    mount DEVICE as overlayfs and write changes there
-#    device must already have kernel mountalbe filesystem on it.
+#  * overlayroot=DEVICE[:DEVICE] or overlayroot=device:PARAMETERS
+#    mount DEVICE(s) as overlayfs and write changes to the first
+#    device(s) must already have kernel mountalbe filesystem on them.
 #
 #    available parameters are:
 #     * dev: default: "" [REQUIRED]
-#       use given device for backing filesystem.
+#       use given device(s) for backing filesystems.
 #       Note, 'overlayroot=/dev/vdb' is translated to
 #             'overlayrooot=device:dev=/dev/vdb'
 #     * timeout: default: 0
@@ -34,7 +34,9 @@
 #    examples:
 #      overlayroot=/dev/xvdb
 #      overlayroot=/dev/vdb
+#      overlayroot=/dev/vdc:/dev/vdb
 #      overlayroot=device:dev=/dev/sdb,timeout=180
+#      overlayroot=device:dev=/dev/sdc:/dev/sdb,timeout=180
 #      overlayroot=device:dev=LABEL=my-flashdrive,timeout=180
 #
 #  * overlayroot=crypt:PARAMETERS

overlayroot/scripts/init-bottom/overlayroot

@@ -2,6 +2,7 @@
 #  Copyright, 2012 Dustin Kirkland <kirkland@ubuntu.com>
 #  Copyright, 2012 Scott Moser <smoser@ubuntu.com>
 #  Copyright, 2012 Axel Heider
+#  Copyright, 2024 Daniel Ruthardt <druthrdt@linuxfoundation.org>
 #
 #  Based on scripts from
 #    Sebastian P.
@@ -335,7 +336,7 @@ overlayrootify_fstab() {
 	local hash="#" oline="" ospec="" upper="" dirs="" copy_opts="" copy_opt=""
 	local spec file vfstype opts pass freq line ro_line
 	local workdir="" use_orig="" relfile="" needs_workdir=false noauto=""
-	
+
 	[ -f "$input" ] || return 1
 
     cat <<EOF
@@ -671,17 +672,29 @@ case "${overlayroot:-disabled}" in
 			/dev/*) opts="dev=${overlayroot}";;
 			*) opts="${overlayroot#device:}";;
 		esac
-		dev_setup "${opts}" ||
-			fail "failed setup overlay for ${overlayroot} [$opts]${cfgmsg}"
+
+		devices="$(echo -n "$opts" | grep -Eo 'dev=([^,]*)' | cut -d= -f2 | tr ":" "\n" | tac)"
+
+		for device in $devices; do
+			dopts=$(echo "$opts" | sed "s,dev=[^,]*,dev=${device},")
+
+			dev_setup "$dopts" ||
+				fail "failed setup overlay for ${overlayroot} [${dopts}]${cfgmsg}"
+		done
 		mode="device"
-		device="$_RET_DEVICE"
+
+		mountpoints=""
+		i=1; for device in $(echo "$devices" | sed '$d'); do
+			mountpoints="${mountpoints:+${mountpoints}
+}/media/root-ro-${i}"
+		i=$((i+1)); done
 		;;
 	crypt:*)
 		mode="crypt"
 		opts=${overlayroot#crypt:}
 		crypto_setup "${opts}" ||
 			fail "failed setup crypt for ${overlayroot}${cfgmsg}"
-		device="$_RET_DEVICE"
+		devices="$_RET_DEVICE"
 		;;
 	disabled)
 		debug "overlayroot disabled${cfgmsg}"
@@ -713,46 +726,24 @@ else
 fi
 
 debug "swap=$swap recurse=$recurse debug=$OVERLAYROOT_DEBUG dir=$dir_prefix"
-debug "device=$device mode=$mode driver=${overlayroot_driver}"
+debug "devices=$(echo -n "$devices" | tr "\n" ",") mode=$mode driver=${overlayroot_driver}"
 
 [ "$swap" = "0" -o "$swap" = "1" ] ||
 	fail "invalid setting for swap: $swap. must be '0' or '1'"
 [ "$recurse" = "0" -o "$recurse" = "1" ] ||
 	fail "invalid setting for recurse: $recurse. must be '0' or '1'"
 
-log_warn "configuring overlayroot with driver=${overlayroot_driver} mode=$mode opts='$opts' per $used_desc"
-
-# settings based on overlayroot_driver
-workdir=""
-case "${overlayroot_driver}" in
-	overlayfs|overlay)
-		mount_type="${overlayroot_driver}"
-		mount_opts="-o lowerdir=${root_ro},upperdir=${root_rw}/${dir_prefix}"
-		if needs_workdir; then
-			get_workdir "$root_rw" "$dir_prefix" "/"
-			workdir="$_RET"
-			mount_opts="${mount_opts},workdir=$workdir"
-		fi
-		clean_path "${mount_opts} overlayroot ${ROOTMNT}"
-		mount_opts="$_RET"
-		;;
-	aufs)
-		mount_type="aufs"
-		mount_opts="-o dirs=${root_rw}/${dir_prefix}:${root_ro}=ro aufs-root ${ROOTMNT}"
-		;;
-	*)
-		log_fail "invalid overlayroot driver: ${overlayroot_driver}"
-		panic "$MYTAG"
-		;;
-esac
-
 # make the mount point on the init root fs ${root_rw}
 mkdir -p "${root_rw}" ||
 	fail "failed to create ${root_rw}"
 
 # make the mount point on the init root fs ${root_ro}
 mkdir -p "${root_ro}" ||
 	fail "failed to create ${root_ro}"
+for mountpoint in $mountpoints; do
+	mkdir -p "$mountpoint" ||
+		fail "failed to create ${mountpoint}"
+done
 
 # mount the backing device to $root_rw
 if [ "$mode" = "tmpfs" ]; then
@@ -761,15 +752,20 @@ if [ "$mode" = "tmpfs" ]; then
 		fail "failed to create tmpfs"
 else
 	# dev or crypto
-	mount "$device" "${root_rw}" ||
-		fail "failed mount backing device $device"
+	device=$(echo "$devices" | tail -n1)
+	mount "$device" "$root_rw" ||
+		fail "failed mount backing device ${device}"
 fi
 
 mkdir -p "${root_rw}/${dir_prefix}" ||
 	fail "failed to create ${dir_prefix} on ${device}"
 
-[ -z "$workdir" ] || mkdir -p "$workdir" ||
-	fail "failed to create workdir '$workdir' on ${device}"
+i=1; for device in $(echo "$devices" | head -n -1); do
+	mountpoint=$(echo "$mountpoints" | head -n$i | tail -n1)
+	# mount the backing device
+	mount "$device" "$mountpoint" ||
+			fail "failed mount backing device ${device}"
+i=$((i+1)); done
 
 # root is mounted on ${ROOTMNT}, move it to ${ROOT_RO}.
 mount --move "${ROOTMNT}" "${root_ro}" ||
@@ -780,6 +776,44 @@ mount --move "${ROOTMNT}" "${root_ro}" ||
 # "panic". Otherwise the boot process is very likely to fail with even more
 # errors and leave the system in a wired state.
 
+log_warn "configuring overlayroot with driver=${overlayroot_driver} mode=$mode opts='$opts' per $used_desc"
+
+# settings based on overlayroot_driver
+workdir=""
+case "${overlayroot_driver}" in
+	overlayfs|overlay)
+		mount_type="${overlayroot_driver}"
+    lowerdirs="$root_ro"
+    for mountpoint in $mountpoints; do
+      if [ -d "${mountpoint}${dir_prefix}" ]; then
+        lowerdir="${mountpoint}${dir_prefix}"
+      else
+        lowerdir="$mountpoint"
+      fi
+      lowerdirs="${lowerdir}:${lowerdirs}"
+    done
+		mount_opts="-o lowerdir=${lowerdirs},upperdir=${root_rw}/${dir_prefix}"
+		if needs_workdir; then
+			get_workdir "$root_rw" "$dir_prefix" "/"
+			workdir="$_RET"
+			mount_opts="${mount_opts},workdir=$workdir"
+
+			[ -z "$workdir" ] || mkdir -p "$workdir" ||
+				fail "failed to create workdir '${workdir}' on ${device}"
+		fi
+		clean_path "${mount_opts} overlayroot ${ROOTMNT}"
+		mount_opts="$_RET"
+		;;
+	aufs)
+		mount_type="aufs"
+		mount_opts="-o dirs=${root_rw}/${dir_prefix}:${root_ro}=ro aufs-root ${ROOTMNT}"
+		;;
+	*)
+		log_fail "invalid overlayroot driver: ${overlayroot_driver}"
+		panic "$MYTAG"
+		;;
+esac
+
 # mount virtual fs ${ROOTMNT} with rw-fs ${root_rw} on top of ro-fs ${root_ro}.
 debug mount -t "$mount_type" $mount_opts
 mount -t "$mount_type" $mount_opts
@@ -810,6 +844,11 @@ fi
 mkdir -p "${ROOTMNT}/${root_ro}"
 mount --move ${root_ro} "${ROOTMNT}${root_ro}" ||
 	fail "failed to move ${root_ro} to ${ROOTMNT}${root_ro}"
+for mountpoint in $mountpoints; do
+	mkdir -p "${ROOTMNT}${mountpoint}"
+	mount --move "$mountpoint" "${ROOTMNT}${mountpoint}" ||
+		fail "failed to move ${mountpoint} to ${ROOTMNT}${mountpoint}"
+done
 
 # move mount from ${root_rw} to ${ROOTMNT}${root_rw}
 [ -d ${ROOTMNT}${root_rw} ] || mkdir -p ${ROOTMNT}${root_rw}