init-live.sh: try to make a union mount when possible

This patch tries to make a union mount in live image. For example,
if aufs is enabled with the aufs-enable.scc configuration fragment,
the init-live.sh script will use aufs to make a union mount.

Although overlayfs is not supported by Yocto kernel yet, this patch
still takes it into consideration with the expect that the related
code should at least serve as a placeholder.

[YOCTO #1487]
[YOCTO #4761]

(From OE-Core rev: 3cd6fedd815688b2f3fd97a56feb5f8696ebeace)

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 56 insertions, 7 deletions

diff --git a/meta/recipes-core/initrdscripts/files/init-live.sh b/meta/recipes-core/initrdscripts/files/init-live.sh
index ca4135141f..890c56280a 100644
--- a/meta/recipes-core/initrdscripts/files/init-live.sh
+++ b/meta/recipes-core/initrdscripts/files/init-live.sh
@@ -137,15 +137,64 @@ do
   sleep 1
 done
 
+# Try to make a union mount of the root image.
+# If no unification filesystem is available, mount the image read-only.
+mount_and_boot() {
+    mkdir $ROOT_MOUNT
+    mknod /dev/loop0 b 7 0 2>/dev/null
+
+    # determine which unification filesystem to use
+    union_fs_type=""
+    if grep -q -w "overlayfs" /proc/filesystems; then
+        union_fs_type="overlayfs"
+    elif grep -q -w "aufs" /proc/filesystems; then
+        union_fs_type="aufs"
+    else
+        union_fs_type=""
+    fi
+
+    # make a union mount if possible
+    case $union_fs_type in
+        "overlayfs")
+            mkdir -p /rootfs.ro /rootfs.rw
+            if ! mount -o rw,loop,noatime,nodiratime /media/$i/$ISOLINUX/$ROOT_IMAGE /rootfs.ro; then
+                rm -rf /rootfs.ro /rootfs.rw
+                fatal "Could not mount rootfs image"
+            else
+                mount -t tmpfs -o rw,noatime,mode=755 tmpfs /rootfs.rw
+                mount -t overlayfs -o "lowerdir=/rootfs.ro,upperdir=/rootfs.rw" overlayfs $ROOT_MOUNT
+                mkdir -p $ROOT_MOUNT/rootfs.ro $ROOT_MOUNT/rootfs.rw
+                mount --move /rootfs.ro $ROOT_MOUNT/rootfs.ro
+                mount --move /rootfs.rw $ROOT_MOUNT/rootfs.rw
+            fi
+            ;;
+        "aufs")
+            mkdir -p /rootfs.ro /rootfs.rw
+            if ! mount -o rw,loop,noatime,nodiratime /media/$i/$ISOLINUX/$ROOT_IMAGE /rootfs.ro; then
+                rm -rf /rootfs.ro /rootfs.rw
+                fatal "Could not mount rootfs image"
+            else
+                mount -t tmpfs -o rw,noatime,mode=755 tmpfs /rootfs.rw
+                mount -t aufs -o "dirs=/rootfs.rw=rw:/rootfs.ro=ro" aufs $ROOT_MOUNT
+                mkdir -p $ROOT_MOUNT/rootfs.ro $ROOT_MOUNT/rootfs.rw
+                mount --move /rootfs.ro $ROOT_MOUNT/rootfs.ro
+                mount --move /rootfs.rw $ROOT_MOUNT/rootfs.rw
+            fi
+            ;;
+        "")
+            if ! mount -o rw,loop,noatime,nodiratime /media/$i/$ISOLINUX/$ROOT_IMAGE $ROOT_MOUNT ; then
+                fatal "Could not mount rootfs image"
+            fi
+            ;;
+    esac
+
+    # boot the image
+    boot_live_root
+}
+
 case $label in
     boot)
-        mkdir $ROOT_MOUNT
-        mknod /dev/loop0 b 7 0 2>/dev/null
-        if ! $MOUNT -o rw,loop,noatime,nodiratime /media/$i/$ISOLINUX/$ROOT_IMAGE $ROOT_MOUNT ; then
-            fatal "Could not mount rootfs image"
-        else
-            boot_live_root
-        fi
+        mount_and_boot
         ;;
     install|install-efi)
         if [ -f /media/$i/$ISOLINUX/$ROOT_IMAGE ] ; then