gh-153856: Add os.RWF_NOSIGNAL constant (#153858)

RWF_NOSIGNAL was added in Linux 6.18 to prevent pwritev2() from raising SIGPIPE when writing to disconnected pipes or sockets.

fixes gh-153856

Author: benjaminp

Doc/library/os.rst

@@ -1642,6 +1642,7 @@ or `the MSDN <https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windo
    - :data:`RWF_APPEND`
    - :data:`RWF_DONTCACHE`
    - :data:`RWF_ATOMIC`
+   - :data:`RWF_NOSIGNAL`
 
    Return the total number of bytes actually written.
 
@@ -1691,6 +1692,16 @@ or `the MSDN <https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windo
    .. versionadded:: 3.10
 
 
+.. data:: RWF_NOSIGNAL
+
+   Prevent pipe and socket writes from raising :const:`~signal.SIGPIPE`.
+   This flag is meaningful only for :func:`os.pwritev`.
+
+   .. availability:: Linux >= 6.18.
+
+   .. versionadded:: 3.16
+
+
 .. function:: read(fd, n, /)
 
    Read at most *n* bytes from file descriptor *fd*.

Misc/NEWS.d/next/Library/2026-07-17-14-30-00.gh-issue-153856.JEHepm.rst

@@ -0,0 +1 @@
+Add :data:`os.RWF_NOSIGNAL` constant for Linux 6.18+.

Modules/clinic/posixmodule.c.h

@@ -12941,14 +12941,15 @@ following flags:
 - RWF_APPEND
 - RWF_DONTCACHE
 - RWF_ATOMIC
+- RWF_NOSIGNAL
 
 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=b2e352a22f030e9a]*/
+/*[clinic end generated code: output=e3dd3e9d11a6a5c7 input=c202f24f01fa66c9]*/
 {
     Py_ssize_t cnt;
     Py_ssize_t result;
@@ -18246,6 +18247,9 @@ all_ins(PyObject *m)
 #ifdef RWF_APPEND
     if (PyModule_AddIntConstant(m, "RWF_APPEND", RWF_APPEND)) return -1;
 #endif
+#ifdef RWF_NOSIGNAL
+    if (PyModule_AddIntConstant(m, "RWF_NOSIGNAL", RWF_NOSIGNAL)) return -1;
+#endif
 
 /* constants for splice */
 #if defined(HAVE_SPLICE) && defined(__linux__)