Patches #749830, #1144555: allow UNIX mmap size to default to current

file size.

Doc/lib/libmmap.tex

@@ -62,8 +62,10 @@ the underlying file.
                          prot\optional{, access}}}}
   \strong{(\UNIX{} version)} Maps \var{length} bytes from the file
   specified by the file descriptor \var{fileno}, and returns a mmap
-  object.
-
+  object.  If \var{length} is \code{0}, the maximum length of the map
+  will be the current size of the file when \function{mmap(} is
+  called.
+  
   \var{flags} specifies the nature of the mapping.
   \constant{MAP_PRIVATE} creates a private copy-on-write mapping, so
   changes to the contents of the mmap object will be private to this

Lib/test/output/test_mmap

@@ -31,4 +31,6 @@ test_mmap
   Modifying copy-on-write memory map.
   Ensuring copy-on-write maps cannot be resized.
   Ensuring invalid access parameter raises exception.
+  Ensuring that passing 0 as map length sets map size to current file size.
+  Ensuring that passing 0 as map length sets map size to current file size.
  Test passed

Lib/test/test_mmap.py

@@ -311,7 +311,43 @@ def test_both():
     finally:
         os.unlink(TESTFN)
 
+    # test mapping of entire file by passing 0 for map length
+    if hasattr(os, "stat"):
+        print "  Ensuring that passing 0 as map length sets map size to current file size."
+        f = open(TESTFN, "w+")
 
+        try:
+            f.write(2**16 * 'm') # Arbitrary character
+            f.close()
+
+            f = open(TESTFN, "rb+")
+            mf = mmap.mmap(f.fileno(), 0) 
+            verify(len(mf) == 2**16, "Map size should equal file size.")
+            vereq(mf.read(2**16), 2**16 * "m")
+            mf.close()
+            f.close()
+
+        finally:
+            os.unlink(TESTFN)
+    
+    # test mapping of entire file by passing 0 for map length
+    if hasattr(os, "stat"):
+        print "  Ensuring that passing 0 as map length sets map size to current file size."
+        f = open(TESTFN, "w+")
+        try:
+            f.write(2**16 * 'm') # Arbitrary character
+            f.close()
+    
+            f = open(TESTFN, "rb+")
+            mf = mmap.mmap(f.fileno(), 0) 
+            verify(len(mf) == 2**16, "Map size should equal file size.")
+            vereq(mf.read(2**16), 2**16 * "m")
+            mf.close()
+            f.close()
+    
+        finally:
+            os.unlink(TESTFN)
+    
     print ' Test passed'
 
 test_both()

Misc/NEWS

@@ -36,6 +36,9 @@ Core and builtins
 Extension Modules
 -----------------
 
+- Patches #749830, #1144555: allow UNIX mmap size to default to current 
+  file size.
+
 - Added functional.partial().  See PEP309.
 
 - Patch #1093585: raise a ValueError for negative history items in readline.

Modules/mmapmodule.c

@@ -896,11 +896,14 @@ new_mmap_object(PyObject *self, PyObject *args, PyObject *kwdict)
 	/* on OpenVMS we must ensure that all bytes are written to the file */
 	fsync(fd);
 #  endif
-	if (fstat(fd, &st) == 0 && S_ISREG(st.st_mode) &&
-	    (size_t)map_size > st.st_size) {
-		PyErr_SetString(PyExc_ValueError, 
-				"mmap length is greater than file size");
-		return NULL;
+	if (fstat(fd, &st) == 0 && S_ISREG(st.st_mode)) {
+		if (map_size == 0) {
+			map_size = (int)st.st_size;
+		} else if ((size_t)map_size > st.st_size) {
+			PyErr_SetString(PyExc_ValueError, 
+					"mmap length is greater than file size");
+			return NULL;
+		}
 	}
 #endif
 	m_obj = PyObject_New (mmap_object, &mmap_object_type);