classes: files: Extend overlayfs-etc class

Add the ability to expose the lower layer of /etc when mounting overlay.
This is the similar to what overlayroot script from initramfs-framework does.

By default, this option is turned off to keep an old behavior intact.

(From OE-Core rev: 6ad25304abefcbe538db7745e17ac213fa7d0719)

Signed-off-by: Vyacheslav Yurkov <v.yurkov@precitec.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 791e8a8bacce5a7f31f4d7bcbfb17df2967fd258)
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

2 files changed, 13 insertions, 1 deletions

diff --git a/meta/classes/overlayfs-etc.bbclass b/meta/classes/overlayfs-etc.bbclass
index 91afee695c..40116e4c6e 100644
--- a/meta/classes/overlayfs-etc.bbclass
+++ b/meta/classes/overlayfs-etc.bbclass
@@ -34,6 +34,7 @@ OVERLAYFS_ETC_DEVICE ??= ""
 OVERLAYFS_ETC_USE_ORIG_INIT_NAME ??= "1"
 OVERLAYFS_ETC_MOUNT_OPTIONS ??= "defaults"
 OVERLAYFS_ETC_INIT_TEMPLATE ??= "${COREBASE}/meta/files/overlayfs-etc-preinit.sh.in"
+OVERLAYFS_ETC_EXPOSE_LOWER ??= "0"
 
 python create_overlayfs_etc_preinit() {
     overlayEtcMountPoint = d.getVar("OVERLAYFS_ETC_MOUNT_POINT")
@@ -54,13 +55,15 @@ python create_overlayfs_etc_preinit() {
     preinitPath = oe.path.join(d.getVar("IMAGE_ROOTFS"), d.getVar("base_sbindir"), "preinit")
     initBaseName = oe.path.join(d.getVar("base_sbindir"), "init")
     origInitNameSuffix = ".orig"
+    exposeLower = oe.types.boolean(d.getVar('OVERLAYFS_ETC_EXPOSE_LOWER'))
 
     args = {
         'OVERLAYFS_ETC_MOUNT_POINT': overlayEtcMountPoint,
         'OVERLAYFS_ETC_MOUNT_OPTIONS': d.getVar('OVERLAYFS_ETC_MOUNT_OPTIONS'),
         'OVERLAYFS_ETC_FSTYPE': overlayEtcFsType,
         'OVERLAYFS_ETC_DEVICE': overlayEtcDevice,
-        'SBIN_INIT_NAME': initBaseName + origInitNameSuffix if useOrigInit else initBaseName
+        'SBIN_INIT_NAME': initBaseName + origInitNameSuffix if useOrigInit else initBaseName,
+        'OVERLAYFS_ETC_EXPOSE_LOWER': "true" if exposeLower else "false"
     }
 
     if useOrigInit:
diff --git a/meta/files/overlayfs-etc-preinit.sh.in b/meta/files/overlayfs-etc-preinit.sh.in
index 0e80849f12..8db076f4ba 100644
--- a/meta/files/overlayfs-etc-preinit.sh.in
+++ b/meta/files/overlayfs-etc-preinit.sh.in
@@ -18,6 +18,7 @@ mount -t sysfs sysfs /sys
 BASE_OVERLAY_ETC_DIR={OVERLAYFS_ETC_MOUNT_POINT}/overlay-etc
 UPPER_DIR=$BASE_OVERLAY_ETC_DIR/upper
 WORK_DIR=$BASE_OVERLAY_ETC_DIR/work
+LOWER_DIR=$BASE_OVERLAY_ETC_DIR/lower
 
 mkdir -p {OVERLAYFS_ETC_MOUNT_POINT}
 if mount -n -t {OVERLAYFS_ETC_FSTYPE} \
@@ -26,6 +27,14 @@ if mount -n -t {OVERLAYFS_ETC_FSTYPE} \
 then
     mkdir -p $UPPER_DIR
     mkdir -p $WORK_DIR
+
+    if {OVERLAYFS_ETC_EXPOSE_LOWER}; then
+        mkdir -p $LOWER_DIR
+
+        # provide read-only access to original /etc content
+        mount -o bind,ro /etc $LOWER_DIR
+    fi
+
     mount -n -t overlay \
         -o upperdir=$UPPER_DIR \
         -o lowerdir=/etc \