solve conflicts with multiple parallel ctorrents

roles/lmn_vm/files/sync-vm.sh

@@ -23,14 +23,39 @@ download_image() {
 }
 
 torrent_image() {
-    if [[ -f "/lmn/vm/${VM_NAME}.qcow2.torrent" ]]; then
+    if [[ ! -f "/lmn/vm/${VM_NAME}.qcow2.torrent" ]]; then
-      cd /lmn/vm
-      ctorrent -e 0 "${VM_NAME}.qcow2.torrent"
-      /usr/local/bin/vmimage-torrent restart "${VM_NAME}.qcow2"
-    else
       echo "No torrent-File found"
       exit 1
     fi
+    lockfile="/tmp/sync-vm-${VM_NAME}.lock"
+    if ! flock -n "$lockfile" echo "try to acquire lock"; then
+      echo torrent seems to be in process.
+      echo waiting for completion ...
+      flock -w 3600 "$lockfile" echo "...completed"
+      sleep 5
+    else
+      (
+        if ! flock -n 200; then
+	  echo "failed to acquire lock"
+	  echo "Bitte noch einmal starten."
+          echo "Beliebige Taste zum Beenden."
+	  read -n 1
+	  exit 1
+        fi
+        torrent="${VM_NAME}.qcow2.torrent"
+        session="${torrent//./_}"
+        if vmimage-torrent status | grep -qw ^"$session"; then
+          vmimage-torrent stop "${VM_NAME}.qcow2"
+        fi
+        cd /lmn/vm
+        ctorrent -e 0 "${VM_NAME}.qcow2.torrent"
+        /usr/local/bin/vmimage-torrent restart "${VM_NAME}.qcow2"
+        if ! flock -u 200; then
+	  echo failed to drop lock
+	  exit 1
+	fi
+      ) 200>"$lockfile"
+    fi
 }
 
 sync_all_images() {