dd-multi: workaround mount/umount issue

It seems that calling umount directly after mount can lead to a
busy error. With strace on umount the problem goes away. It must
be a very small window. Someone should debug the umount syscall
on this. It is reproducable with:

    ./dd-multi.sh lx-trainer.img /dev/sdx

(i.e. regular training image and no layers)

Implement a workaround for this for now.

From the comments...

If there were no layer files added, umount might return a busy
error since we just mounted. (Possibly a kernel bug.) By
accessing the filesytem before unmounting it, the mount/umount
problem seems to go away. Use "ls" to access the filesystem.

Signed-off-by: John Ogness <john.ogness@linutronix.de>

1 files changed, 6 insertions, 0 deletions

diff --git a/lx-trainer-vm/dd-multi.sh b/lx-trainer-vm/dd-multi.sh
index 2a0f9f9..f74171d 100755
--- a/lx-trainer-vm/dd-multi.sh
+++ b/lx-trainer-vm/dd-multi.sh
@@ -160,6 +160,12 @@ for tarball in $LAYERS; do
 done
 
 for dest in $DESTS; do
+	# If there were no layer files added, umount might return a busy
+	# error since we just mounted. (Possibly a kernel bug.) By
+	# accessing the filesytem before unmounting it, the mount/umount
+	# problem seems to go away. Use "ls" to access the filesystem. 
+	ls ${TMP_ROOT}${dest}${ROOTPT}/home/ > /dev/null
+
 	# unmount partitions
 	umount ${TMP_ROOT}${dest}${ROOTPT}/home
 	umount ${TMP_ROOT}${dest}${ROOTPT}