avoid stale filehandle issues, fixes #3265

src/borg/constants.py

@@ -52,6 +52,8 @@ LIST_SCAN_LIMIT = 100000
 
 DEFAULT_SEGMENTS_PER_DIR = 1000
 
+FD_MAX_AGE = 4 * 60  # 4 minutes
+
 CHUNK_MIN_EXP = 19  # 2**19 == 512kiB
 CHUNK_MAX_EXP = 23  # 2**23 == 8MiB
 HASH_WINDOW_SIZE = 0xfff  # 4095B

src/borg/lrucache.py

@@ -39,6 +39,12 @@ class LRUCache:
         self._lru.append(key)
         return value
 
+    def upd(self, key, value):
+        # special use only: update the value for an existing key without having to dispose it first
+        # this method complements __setitem__ which should be used for the normal use case.
+        assert key in self._cache, "Unexpected attempt to update a non-existing item."
+        self._cache[key] = value
+
     def clear(self):
         for value in self._cache.values():
             self._dispose(value)

src/borg/repository.py

@@ -3,6 +3,7 @@ import mmap
 import os
 import shutil
 import struct
+import time
 from binascii import hexlify, unhexlify
 from collections import defaultdict
 from configparser import ConfigParser
@@ -1135,8 +1136,7 @@ class LoggedIO:
 
     def __init__(self, path, limit, segments_per_dir, capacity=90):
         self.path = path
-        self.fds = LRUCache(capacity,
-                            dispose=self.close_fd)
+        self.fds = LRUCache(capacity, dispose=self._close_fd)
         self.segment = 0
         self.limit = limit
         self.segments_per_dir = segments_per_dir
@@ -1148,7 +1148,8 @@ class LoggedIO:
         self.fds.clear()
         self.fds = None  # Just to make sure we're disabled
 
-    def close_fd(self, fd):
+    def _close_fd(self, ts_fd):
+        ts, fd = ts_fd
         safe_fadvise(fd.fileno(), 0, 0, 'DONTNEED')
         fd.close()
 
@@ -1262,13 +1263,31 @@ class LoggedIO:
         return self._write_fd
 
     def get_fd(self, segment):
-        try:
-            return self.fds[segment]
-        except KeyError:
+        # note: get_fd() returns a fd with undefined file pointer position,
+        # so callers must always seek() to desired position afterwards.
+        now = time.monotonic()
+
+        def open_fd():
             fd = open(self.segment_filename(segment), 'rb')
-            self.fds[segment] = fd
+            self.fds[segment] = (now, fd)
             return fd
 
+        try:
+            ts, fd = self.fds[segment]
+        except KeyError:
+            fd = open_fd()
+        else:
+            if now - ts > FD_MAX_AGE:
+                # we do not want to touch long-unused file handles to
+                # avoid ESTALE issues (e.g. on network filesystems).
+                del self.fds[segment]
+                fd = open_fd()
+            else:
+                # fd is fresh enough, so we use it.
+                # also, we update the timestamp of the lru cache entry.
+                self.fds.upd(segment, (now, fd))
+        return fd
+
     def close_segment(self):
         # set self._write_fd to None early to guard against reentry from error handling code paths:
         fd, self._write_fd = self._write_fd, None