bpo-24658: os.read() reuses _PY_READ_MAX (pythonGH-10657)

os_read_impl() now also truncates the size to _PY_READ_MAX
on macOS, to avoid to allocate a larger buffer even if _Py_read() is
limited to _PY_READ_MAX bytes (ex: INT_MAX on macOS).

Author: vstinner

Modules/posixmodule.c

@@ -8410,11 +8410,7 @@ os_read_impl(PyObject *module, int fd, Py_ssize_t length)
         return posix_error();
     }
 
-#ifdef MS_WINDOWS
-    /* On Windows, the count parameter of read() is an int */
-    if (length > INT_MAX)
-        length = INT_MAX;
-#endif
+    length = Py_MIN(length, _PY_READ_MAX);
 
     buffer = PyBytes_FromStringAndSize((char *)NULL, length);
     if (buffer == NULL)