Return st_nlink of 1 for mirrored index files

GitLab issue #676. Thanks to Ezio Vernacotola (@eziove) for the
report and solution.

Signed-off-by: Roberto Rosario <roberto.rosario@mayan-edms.com>

HISTORY.rst

@@ -23,6 +23,8 @@
 - Move Celery and Django Celery dependencies
   to the task manager app.
 - Improve dependecies app tests.
+- Return st_nlink of 1 files in mirrored indexes. GitLab issue #676.
+  Thanks to Ezio Vernacotola (@eziove) for the report and solution.
 
 3.2.8 (2019-10-01)
 ==================

docs/releases/3.2.9.rst

@@ -99,6 +99,7 @@ Backward incompatible changes
 Bugs fixed or issues closed
 ---------------------------
 
+- :gitlab-issue:`676` Access fuse mounted index via samba
 - :gitlab-issue:`677` Django start before PostgreSQL is up.
 - :forum-topic:`1347` Workflow state action: perform a POST request
 

mayan/apps/mirroring/filesystems.py

@@ -146,6 +146,9 @@ class IndexFilesystem(Operations):
         if not result:
             raise FuseOSError(ENOENT)
 
+        # st_nlink tracks the number of hard links to a file.
+        # Must be 2 for directories and at least 1 for files
+        # https://www.gnu.org/software/libc/manual/html_node/Attribute-Meanings.html
         if isinstance(result, IndexInstanceNode):
             return {
                 'st_mode': (S_IFDIR | DIRECTORY_MODE), 'st_ctime': now,
@@ -161,7 +164,8 @@ class IndexFilesystem(Operations):
                     result.latest_version.timestamp.replace(tzinfo=None) - result.latest_version.timestamp.utcoffset() - datetime.datetime(1970, 1, 1)
                 ).total_seconds(),
                 'st_atime': now,
-                'st_size': result.size
+                'st_size': result.size,
+                'st_nlink': 1
             }
 
     def open(self, path, flags):