Patch #1407135, bug #1424041, make mmap.mmap(-1, length) work the same

on both Unix (SVR4 and BSD) and Windows.  Restores behaviour of passing -1
for anonymous memory on Unix.  Use MAP_ANONYMOUS instead of _ANON since
the latter is deprecated according to Linux (gentoo) man pages.

Should we continue to allow mmap.mmap(0, length) to work on Windows?
0 is a valid fd.

Will backport bugfix portions.

Doc/lib/libmmap.tex

@@ -37,7 +37,8 @@ taken from the specified file.  Assignment to an
 exception.  Assignment to an \constant{ACCESS_WRITE} memory map
 affects both memory and the underlying file.  Assignment to an
 \constant{ACCESS_COPY} memory map affects memory but does not update
-the underlying file.
+the underlying file.  \versionchanged[To map anonymous memory,
+-1 should be passed as the fileno along with the length]{2.5}
 
 \begin{funcdesc}{mmap}{fileno, length\optional{, tagname\optional{, access}}}
   \strong{(Windows version)} Maps \var{length} bytes from the file

Lib/test/output/test_mmap

@@ -34,4 +34,5 @@ test_mmap
   Try opening a bad file descriptor...
   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.
+  anonymous mmap.mmap(-1, PAGESIZE)...
  Test passed

Lib/test/test_mmap.py

@@ -283,7 +283,7 @@ def test_both():
 
     print '  Try opening a bad file descriptor...'
     try:
-        mmap.mmap(-1, 4096)
+        mmap.mmap(-2, 4096)
     except mmap.error:
         pass
     else:
@@ -380,6 +380,16 @@ def test_both():
     finally:
         os.unlink(TESTFN)
 
-    print ' Test passed'
+def test_anon():
+    print "  anonymous mmap.mmap(-1, PAGESIZE)..."
+    m = mmap.mmap(-1, PAGESIZE)
+    for x in xrange(PAGESIZE):
+        verify(m[x] == '\0', "anonymously mmap'ed contents should be zero")
+
+    for x in xrange(PAGESIZE):
+        m[x] = ch = chr(x & 255)
+        vereq(m[x], ch)
 
 test_both()
+test_anon()
+print ' Test passed'

Misc/NEWS

@@ -216,6 +216,10 @@ Core and builtins
 Extension Modules
 -----------------
 
+- Patch #1407135, bug #1424041: harmonize mmap behavior of anonymous memory.
+  mmap.mmap(-1, size) now returns anonymous memory in both Unix and Windows.
+  mmap.mmap(0, size) should not be used on Windows for anonymous memory.
+
 - Patch #1422385: The nis module now supports access to domains other
   than the system default domain.
 

Modules/mmapmodule.c

@@ -54,6 +54,11 @@ my_getpagesize(void)
 #include <string.h>
 #include <sys/types.h>
 
+/* maybe define MAP_ANON in terms of MAP_ANONYMOUS */
+#if !defined(MAP_ANONYMOUS) && defined(MAP_ANON)
+#  define MAP_ANONYMOUS MAP_ANON
+#endif
+
 static PyObject *mmap_module_error;
 
 typedef enum
@@ -863,6 +868,7 @@ new_mmap_object(PyObject *self, PyObject *args, PyObject *kwdict)
 	PyObject *map_size_obj = NULL;
 	int map_size;
 	int fd, flags = MAP_SHARED, prot = PROT_WRITE | PROT_READ;
+	int devzero = -1;
 	int access = (int)ACCESS_DEFAULT;
 	static const char *keywords[] = {"fileno", "length", 
                                          "flags", "prot", 
@@ -921,15 +927,41 @@ new_mmap_object(PyObject *self, PyObject *args, PyObject *kwdict)
 	m_obj->data = NULL;
 	m_obj->size = (size_t) map_size;
 	m_obj->pos = (size_t) 0;
-	m_obj->fd = dup(fd);
-	if (m_obj->fd == -1) {
-		Py_DECREF(m_obj);
-		PyErr_SetFromErrno(mmap_module_error);
-		return NULL;
+	if (fd == -1) {
+		m_obj->fd = -1;
+		/* Assume the caller wants to map anonymous memory.
+		   This is the same behaviour as Windows.  mmap.mmap(-1, size)
+		   on both Windows and Unix map anonymous memory.
+		*/
+#ifdef MAP_ANONYMOUS
+		/* BSD way to map anonymous memory */
+		flags |= MAP_ANONYMOUS;
+#else
+		/* SVR4 method to map anonymous memory is to open /dev/zero */
+		fd = devzero = open("/dev/zero", O_RDWR);
+		if (devzero == -1) {
+			Py_DECREF(m_obj);
+			PyErr_SetFromErrno(mmap_module_error);
+			return NULL;
+		}
+#endif
+	} else {
+		m_obj->fd = dup(fd);
+		if (m_obj->fd == -1) {
+			Py_DECREF(m_obj);
+			PyErr_SetFromErrno(mmap_module_error);
+			return NULL;
+		}
 	}
+
 	m_obj->data = mmap(NULL, map_size, 
 			   prot, flags,
 			   fd, 0);
+
+	if (devzero != -1) {
+		close(devzero);
+	}
+
 	if (m_obj->data == (char *)-1) {
 	        m_obj->data = NULL;
 		Py_DECREF(m_obj);
@@ -986,8 +1018,15 @@ new_mmap_object(PyObject *self, PyObject *args, PyObject *kwdict)
 	if (map_size < 0)
 		return NULL;
 	
-	/* if an actual filename has been specified */
-	if (fileno != 0) {
+	/* assume -1 and 0 both mean invalid filedescriptor
+	   to 'anonymously' map memory.
+	   XXX: fileno == 0 is a valid fd, but was accepted prior to 2.5.
+	   XXX: Should this code be added?
+	   if (fileno == 0)
+	   	PyErr_Warn(PyExc_DeprecationWarning,
+			   "don't use 0 for anonymous memory");
+	 */
+	if (fileno != -1 && fileno != 0) {
 		fh = (HANDLE)_get_osfhandle(fileno);
 		if (fh==(HANDLE)-1) {
 			PyErr_SetFromErrno(mmap_module_error);
@@ -1123,10 +1162,10 @@ PyMODINIT_FUNC
 	PyDict_SetItemString (dict, "MAP_EXECUTABLE",
 			      PyInt_FromLong(MAP_EXECUTABLE) );
 #endif
-#ifdef MAP_ANON
-	PyDict_SetItemString (dict, "MAP_ANON", PyInt_FromLong(MAP_ANON) );
+#ifdef MAP_ANONYMOUS
+	PyDict_SetItemString (dict, "MAP_ANON", PyInt_FromLong(MAP_ANONYMOUS) );
 	PyDict_SetItemString (dict, "MAP_ANONYMOUS",
-			      PyInt_FromLong(MAP_ANON) );
+			      PyInt_FromLong(MAP_ANONYMOUS) );
 #endif
 
 	PyDict_SetItemString (dict, "PAGESIZE",