Use pip fallocate package rather than hand-rolling

nilmdb/utils/fallocate.py

@@ -1,49 +1,19 @@
 # Implementation of hole punching via fallocate, if the OS
 # and filesystem support it.
 
-try:
-    import os
-    import ctypes
-    import ctypes.util
-
-    def make_fallocate():
-        libc_name = ctypes.util.find_library('c')
-        libc = ctypes.CDLL(libc_name, use_errno=True)
-
-        _fallocate = libc.fallocate
-        _fallocate.restype = ctypes.c_int
-        _fallocate.argtypes = [ ctypes.c_int, ctypes.c_int,
-                                ctypes.c_int64, ctypes.c_int64 ]
-
-        del libc
-        del libc_name
-
-        def fallocate(fd, mode, offset, len_):
-            res = _fallocate(fd, mode, offset, len_)
-            if res != 0: # pragma: no cover
-                errno = ctypes.get_errno()
-                raise IOError(errno, os.strerror(errno))
-        return fallocate
-
-    fallocate = make_fallocate()
-    del make_fallocate
-except Exception: # pragma: no cover
-    fallocate = None
-
-FALLOC_FL_KEEP_SIZE = 0x01
-FALLOC_FL_PUNCH_HOLE = 0x02
+import fallocate
 
 def punch_hole(filename, offset, length, ignore_errors = True):
     """Punch a hole in the file.  This isn't well supported, so errors
     are ignored by default."""
     try:
-        if fallocate is None: # pragma: no cover
-            raise IOError("fallocate not available")
         with open(filename, "r+") as f:
-            fallocate(f.fileno(),
-                      FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE,
-                      offset, length)
-    except IOError: # pragma: no cover
+            fallocate.fallocate(
+                f.fileno(),
+                offset,
+                length,
+                fallocate.FALLOC_FL_KEEP_SIZE | fallocate.FALLOC_FL_PUNCH_HOLE)
+    except Exception:
         if ignore_errors:
             return
         raise

tests/test_misc.py

@@ -52,3 +52,21 @@ class TestMisc(object):
         nilmdb.utils.atomic.replace_file(fn, b"goodbye, world")
         with open(fn, "rb") as f:
             eq_(f.read(), b"goodbye, world")
+
+    def test_punch(self):
+        fn = b"tests/misc-testdb/punchit"
+        try:
+            os.mkdir(os.path.dirname(fn))
+        except FileExistsError:
+            pass
+        with open(fn, "wb") as f:
+            f.write(b"hello, world")
+        nilmdb.utils.fallocate.punch_hole(fn, 3, 5)
+        with open(fn, "rb") as f:
+            eq_(f.read(), b"hel\0\0\0\0\0orld")
+        with assert_raises(OSError):
+            nilmdb.utils.fallocate.punch_hole(fn, 1, -1, False)
+        with assert_raises(OSError):
+            nilmdb.utils.fallocate.punch_hole("/", 1, 1, False)
+        # no exception because we ignore errors by default
+        nilmdb.utils.fallocate.punch_hole(fn, 1, -1)