common/rc: new functions for multi-level mount/umount operations

When I try to write cases about mount shared subtrees test, I find I
always need to do many mount operations, then then umount those
mount point one by one.

To make the code clear, I use a stack to save mounted points
sequentially, then I write 3 common functions to operate this stack.

1. The global stack named MOUNTED_POINT_STACK
2. _get_mount() accepts mount parameters like _mount() does, but the
   mountpoint parameter must be the last one. It will run the
   mount operation and push the mountpoint name into stack.
3. _put_mount() doesn't need any parameter. It will pop the newest
   mountpoint name from the stack, and umount it.
4. _clear_mount_stack() doesn't need any parameter either. It will
   umount all mountpoints in the stack sequentially, and set
   MOUNTED_POINT_STACK=""

Generally, the _clear_mount_stack() function also can be used as
_init_mount_stack() at the beginning of a case. Because it will
prepare an empty stack.

[eguan: add comments and fix code style]

Signed-off-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>

diff --git a/common/rc b/common/rc
index 76515e2bd6486abfdf33d212fa49518ee5793bc2..f5bc03231cc23daa5d45b6982f0ea3652925422e 100644 (file)
--- a/common/rc
+++ b/common/rc
@@ -160,6 +160,41 @@ _mount()
     $MOUNT_PROG `_mount_ops_filter $*`
 }
 
+# Call _mount to do mount operation but also save mountpoint to
+# MOUNTED_POINT_STACK. Note that the mount point must be the last parameter
+_get_mount()
+{
+       local mnt_point=${!#}
+
+       _mount $*
+       if [ $? -eq 0 ]; then
+               MOUNTED_POINT_STACK="$mnt_point $MOUNTED_POINT_STACK"
+       else
+               return 1
+       fi
+}
+
+# Unmount the last mounted mountpoint in MOUNTED_POINT_STACK
+# and return it to caller
+_put_mount()
+{
+       local last_mnt=`echo $MOUNTED_POINT_STACK | awk '{print $1}'`
+
+       if [ -n "$last_mnt" ]; then
+               $UMOUNT_PROG $last_mnt
+       fi
+       MOUNTED_POINT_STACK=`echo $MOUNTED_POINT_STACK | cut -d\  -f2-`
+}
+
+# Unmount all mountpoints in MOUNTED_POINT_STACK and clear the stack
+_clear_mount_stack()
+{
+       if [ -n "$MOUNTED_POINT_STACK" ]; then
+               $UMOUNT_PROG $MOUNTED_POINT_STACK
+       fi
+       MOUNTED_POINT_STACK=""
+}
+
 _scratch_options()
 {
     type=$1