[PATCH] wic-img: Fix bind mounting

[Jan Kiszka <jan.kiszka@siemens.com>]

This addresses two issues of the current code:

 - we must make the bind mount of STAGING_DIR private because it will
   otherwise pick up bind mounts done underneath it in the various
   rootfs used by parallel targets

 - locking was missing to make check and mount atomic, just like we do
   inside buildchroot_do_mounts

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

My theory on what went wrong /wrt rbind-mounted /sys and /dev: As the
bind-mounting of STAGING_DIR of a wic target (qemu-amd64) eventually
started to contain shared(!) bind-mounts of parallel targets (qemu-
armhf, qemu-arm64), and all those stick to the end, isar_handler started
to umount their now also shared /dev and /sys mounts. And that
destroyed the host mounts.

Lesson to be recalled: never paper over issues that were not yet fully
understood. They may point to sleeping problems that will only bite you
again later.

 meta/classes/wic-img.bbclass | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/meta/classes/wic-img.bbclass b/meta/classes/wic-img.bbclass
index 225463e..76602d8 100644
--- a/meta/classes/wic-img.bbclass
+++ b/meta/classes/wic-img.bbclass
@@ -87,11 +87,14 @@ do_build[stamp-extra-info] = "${DISTRO}-${DISTRO_ARCH}"
 
 do_wic_image() {
     buildchroot_do_mounts
-    for dir in ${BBLAYERS} ${STAGING_DIR} ${ISARROOT}/scripts; do
-	sudo mkdir -p ${BUILDCHROOT_DIR}/$dir
-        mountpoint ${BUILDCHROOT_DIR}/$dir >/dev/null 2>&1 \
-        || sudo mount --bind $dir ${BUILDCHROOT_DIR}/$dir
-    done
+    sudo flock ${MOUNT_LOCKFILE} -c ' \
+        for dir in ${BBLAYERS} ${STAGING_DIR} ${ISARROOT}/scripts; do
+            mkdir -p ${BUILDCHROOT_DIR}/$dir
+            if ! mountpoint ${BUILDCHROOT_DIR}/$dir >/dev/null 2>&1; then
+                mount --bind --make-private $dir ${BUILDCHROOT_DIR}/$dir
+            fi
+        done
+        '
     export FAKEROOTCMD=${FAKEROOTCMD}
     export BUILDDIR=${BUILDDIR}
     export MTOOLS_SKIP_CHECK=1
-- 
2.16.4