gh-143474: Add os.RWF_ATOMIC constant

Doc/library/os.rst

@@ -1556,6 +1556,15 @@ or `the MSDN <https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windo
    .. versionadded:: 3.15
 
 
+.. data:: RWF_ATOMIC
+
+   Write data atomically. Requires alignment to the device's atomic write unit.
+
+   .. availability:: Linux >= 6.11
+
+   .. versionadded:: next
+
+
 .. function:: ptsname(fd, /)
 
    Return the name of the slave pseudo-terminal device associated with the
@@ -1598,6 +1607,7 @@ or `the MSDN <https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windo
    - :data:`RWF_SYNC`
    - :data:`RWF_APPEND`
    - :data:`RWF_DONTCACHE`
+   - :data:`RWF_ATOMIC`
 
    Return the total number of bytes actually written.
 

Misc/NEWS.d/next/Library/2026-01-06-12-00-00.gh-issue-143474.cQM4VA.rst

@@ -0,0 +1 @@
+Add :data:`os.RWF_ATOMIC` constant for Linux 6.11+.

Modules/posixmodule.c

@@ -12863,14 +12863,15 @@ The flags argument contains a bitwise OR of zero or more of the following flags:
 - RWF_SYNC
 - RWF_APPEND
 - RWF_DONTCACHE
+- RWF_ATOMIC
 
 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=664a67626d485665]*/
+/*[clinic end generated code: output=e3dd3e9d11a6a5c7 input=7de72245873f56bf]*/
 {
     Py_ssize_t cnt;
     Py_ssize_t result;
@@ -18120,6 +18121,9 @@ all_ins(PyObject *m)
 #ifdef RWF_DONTCACHE
     if (PyModule_AddIntConstant(m, "RWF_DONTCACHE", RWF_DONTCACHE)) return -1;
 #endif
+#ifdef RWF_ATOMIC
+    if (PyModule_AddIntConstant(m, "RWF_ATOMIC", RWF_ATOMIC)) return -1;
+#endif
 #ifdef RWF_APPEND
     if (PyModule_AddIntConstant(m, "RWF_APPEND", RWF_APPEND)) return -1;
 #endif