sync: Add optional check for mounted mountpoint(s)

If the systems being synced by bitpocket are syncing a special mounted
filesystem, then a check can be added to ensure the filesystem is mounted
before the sync will begin. This allows for bitpocket to gracefully abort the
sync instead of deleting all the local or remote data because of the missing
mount (making the sync target appear empty like all the files were removed).

bin/bitpocket

@@ -20,6 +20,7 @@ SLOW_SYNC_FILE="$TMP_DIR/slow"
 RSYNC_RSH="ssh"
 REMOTE_BACKUPS=false
 BACKUPS=true
+REMOTE_MOUNTPOINT=false
 
 # Default command-line options and such
 COMMANDS=()
@@ -134,6 +135,13 @@ REMOTE_BACKUPS=false
 # SLOW_SYNC_TIME=10
 # SLOW_SYNC_START_CMD="notify-send 'BitPocket sync in progress...'"
 # SLOW_SYNC_STOP_CMD="notify-send 'BitPocket sync finished'"
+
+## Indicate a remote mount point. If this is set and the mountpoint is not
+## mounted, then the bitpocket sync will abort. This addresses situations where
+## a sync target appears empty because it is not mounted.  Such a sync might
+## result in all local or remote data disappearing. Give the expected
+## mountpoint of the local and/or remote target.
+# REMOTE_MOUNTPOINT=/
 EOF
 
   echo "Initialized bitpocket directory at `pwd`"
@@ -340,6 +348,7 @@ function analyse {
 # Do the actual synchronization
 function sync {
   assert_dotdir
+  assert_mountpoints
   acquire_lock
   acquire_remote_lock
 
@@ -515,6 +524,24 @@ function assert_dotdir {
   mkdir -p "$STATE_DIR"
 }
 
+function assert_mountpoints {
+    if [[ ${REMOTE_MOUNTPOINT} != false ]]
+    then
+        # Sanity check -- ensure mountpoint is a parent of local target
+        if [[ "${REMOTE_PATH:0:${#REMOTE_MOUNTPOINT}}" != "${REMOTE_MOUNTPOINT}" ]]
+        then
+            echo -e "${YELLOW}warning: Remote mount point is not a parent of '${REMOTE_PATH}'${CLEAR}"
+        fi
+
+        $REMOTE_RUNNER "mount | grep -E '\s${REMOTE_MOUNTPOINT}\s'" &> /dev/null
+        if [[ $? != 0 ]]
+        then
+            echo -e "${RED}fatal: Remote sync target is not mounted${CLEAR}"
+            exit 4
+        fi
+    fi
+}
+
 function cleanup {
   release_lock
   release_remote_lock