feat (singularity): allow to mount local path rw

Author: chaen

docs/source/AdministratorGuide/Resources/storage.rst

@@ -282,6 +282,12 @@ If the local path follows the DIRAC convention (i.e. finishes with the LFN), the
       {
         Protocol = file
         Path = /mnt/lustre_3/storm_3/lhcbdisk/
+        # Note that rw is very dangerous
+        # as it allows the payload to delete
+        # anything in the mounted folder.
+        # You should use this option only in
+        # very controled environment (without user jobs as well)
+        MountOptions = rw # ro by default
         Host = localhost
         Access = local
       }

src/DIRAC/Resources/Computing/SingularityComputingElement.py

@@ -387,7 +387,12 @@ def submitJob(self, executableFile, proxy=None, **kwargs):
                     continue
 
                 mountedPath = se.getStorageParameters(protocol="file")["Value"]["Path"]
-                bindPaths.append(f"{mountedPath}:{mountedPath}:ro")
+                mountOptions = se.getStorageParameters(protocol="file")["Value"].get("MountOptions", "ro")
+                if mountOptions not in ("rw", "ro"):
+                    self.log.warn(f"Unknown mount mode: {mountOptions}")
+                    continue
+
+                bindPaths.append(f"{mountedPath}:{mountedPath}:{mountOptions}")
             except KeyError:
                 pass