bpo-37129: Add os.RWF_APPEND flag for os.pwritev

Doc/library/os.rst

@@ -1211,6 +1211,7 @@ or `the MSDN <https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windo
 
    - :data:`RWF_DSYNC`
    - :data:`RWF_SYNC`
+   - :data:`RWF_APPEND`
 
    Return the total number of bytes actually written.
 
@@ -1228,8 +1229,8 @@ or `the MSDN <https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windo
 
 .. data:: RWF_DSYNC
 
-   Provide a per-write equivalent of the :data:`O_DSYNC` ``open(2)`` flag. This
-   flag effect applies only to the data range written by the system call.
+   Provide a per-write equivalent of the :data:`O_DSYNC` :func:`os.open` flag.
+   This flag effect applies only to the data range written by the system call.
 
    .. availability:: Linux 4.7 and newer.
 
@@ -1238,14 +1239,28 @@ or `the MSDN <https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windo
 
 .. data:: RWF_SYNC
 
-   Provide a per-write equivalent of the :data:`O_SYNC` ``open(2)`` flag. This
-   flag effect applies only to the data range written by the system call.
+   Provide a per-write equivalent of the :data:`O_SYNC` :func:`os.open` flag.
+   This flag effect applies only to the data range written by the system call.
 
    .. availability:: Linux 4.7 and newer.
 
    .. versionadded:: 3.7
 
 
+.. data:: RWF_APPEND
+
+    Provide a per-write equivalent of the :data:`O_APPEND` :func:`os.open`
+    flag. This flag is meaningful only for :func:`os.pwritev`, and its
+    effect applies only to the data range written by the system call. The
+    *offset* argument does not affect the write operation; the data is always
+    appended to the end of the file. However, if the *offset* argument is
+    ``-1``, the current file *offset* is updated.
+
+   .. availability:: Linux 4.16 and newer.
+
+   .. versionadded:: 3.10
+
+
 .. function:: read(fd, n)
 
    Read at most *n* bytes from file descriptor *fd*.

Misc/NEWS.d/next/Library/2020-05-23-04-18-00.bpo-37129.YoYoYo.rst

@@ -0,0 +1 @@
+Add a new :data:`os.RWF_APPEND` flag for :func:`os.pwritev`.

Modules/posixmodule.c

@@ -9778,14 +9778,15 @@ The flags argument contains a bitwise OR of zero or more of the following flags:
 
 - RWF_DSYNC
 - RWF_SYNC
+- RWF_APPEND
 
 Using non-zero flags requires Linux 4.7 or newer.
 [clinic start generated code]*/
 
 static Py_ssize_t
 os_pwritev_impl(PyObject *module, int fd, PyObject *buffers, Py_off_t offset,
                 int flags)
-/*[clinic end generated code: output=e3dd3e9d11a6a5c7 input=803dc5ddbf0cfd3b]*/
+/*[clinic end generated code: output=e3dd3e9d11a6a5c7 input=35358c327e1a2a8e]*/
 {
     Py_ssize_t cnt;
     Py_ssize_t result;
@@ -14509,6 +14510,9 @@ all_ins(PyObject *m)
 #ifdef RWF_NOWAIT
     if (PyModule_AddIntConstant(m, "RWF_NOWAIT", RWF_NOWAIT)) return -1;
 #endif
+#ifdef RWF_APPEND
+    if (PyModule_AddIntConstant(m, "RWF_APPEND", RWF_APPEND)) return -1;
+#endif
 
 /* constants for posix_spawn */
 #ifdef HAVE_POSIX_SPAWN