bpo-34663: Add support for POSIX_SPAWN_USEVFORK in posix_spawn when available

Doc/library/os.rst

@@ -3396,7 +3396,7 @@ written in Python, such as a mail server's external command delivery program.
 
 .. function:: posix_spawn(path, argv, env, *, file_actions=None, \
                           setpgroup=None, resetids=False, setsigmask=(), \
-                          setsigdef=(), scheduler=None)
+                          setsigdef=(), scheduler=None, use_vfork=False)
 
    Wraps the :c:func:`posix_spawn` C library API for use from Python.
 
@@ -3435,22 +3435,22 @@ written in Python, such as a mail server's external command delivery program.
    :c:func:`posix_spawn_file_actions_adddup2` API calls used to prepare
    for the :c:func:`posix_spawn` call itself.
 
-   The *setpgroup* argument will set the process group of the child to the value
-   specified. If the value specified is 0, the child's process group ID will be
-   made the same as its process ID. If the value of *setpgroup* is not set, the
-   child will inherit the parent's process group ID. This argument corresponds
-   to the C library :c:data:`POSIX_SPAWN_SETPGROUP` flag.
+   The *setpgroup* argument will set the process group of the child process to
+   the value specified. If the value specified is 0, the child's process group
+   ID will be made the same as its process ID. If the value of *setpgroup* is
+   not set, the child process will inherit the parent's process group ID. This
+   argument corresponds to the C library :c:data:`POSIX_SPAWN_SETPGROUP` flag.
 
    If the *resetids* argument is ``True`` it will reset the effective UID and
-   GID of the child to the real UID and GID of the parent process. If the
-   argument is ``False``, then the child retains the effective UID and GID of
-   the parent. In either case, if the set-user-ID and set-group-ID permission
-   bits are enabled on the executable file, their effect will override the
-   setting of the effective UID and GID. This argument corresponds to the C
-   library :c:data:`POSIX_SPAWN_RESETIDS` flag.
+   GID of the child process to the real UID and GID of the parent process. If
+   the argument is ``False``, then the child process retains the effective UID
+   and GID of the parent. In either case, if the set-user-ID and set-group-ID
+   permission bits are enabled on the executable file, their effect will
+   override the setting of the effective UID and GID. This argument corresponds
+   to the C library :c:data:`POSIX_SPAWN_RESETIDS` flag.
 
    The *setsigmask* argument will set the signal mask to the signal set
-   specified. If the parameter is not used, then the child inherits the
+   specified. If the parameter is not used, then the child process inherits the
    parent's signal mask. This argument corresponds to the C library
    :c:data:`POSIX_SPAWN_SETSIGMASK` flag.
 
@@ -3465,6 +3465,13 @@ written in Python, such as a mail server's external command delivery program.
    :c:data:`POSIX_SPAWN_SETSCHEDPARAM` and :c:data:`POSIX_SPAWN_SETSCHEDULER`
    flags.
 
+  If the value of *use_vfork* is true, the child process will be created using
+  :c:func:`vfork` instead of :c:func:`fork`. This corresponds to the GNU
+  specific flag :c:data:`POSIX_SPAWN_USEVFORK`. If the flag is not available on
+  the platform, :exc:`NotImplementedError` will be raised.
+
+   Availability: Unix. Using *use_vfork* is only available on Linux.
+
    .. versionadded:: 3.7
 
 

Lib/test/test_posix.py

@@ -1790,6 +1790,20 @@ def test_dup2(self):
         with open(dupfile) as f:
             self.assertEqual(f.read(), 'hello')
 
+    def test_use_vfork(self):
+        args = self.python_args('-c', 'pass')
+        try:
+            pid = posix.posix_spawn(
+                args[0],
+                args,
+                os.environ,
+                use_vfork=True
+            )
+        except NotImplementedError as exc:
+            raise self.skipTest(str(exc))
+        else:
+            self.assertEqual(os.waitpid(pid, 0), (pid, 0))
+
 
 def test_main():
     try:

Misc/NEWS.d/next/Core and Builtins/2018-09-13-11-14-38.bpo-34663.BtJz-5.rst

@@ -0,0 +1,3 @@
+Added support for `use_vfork` parameter of :func:`os.posix_spawn`, which
+allows to use ``POSIX_SPAWN_USEVFORK`` constant when the flag is available
+in the system.

Modules/posixmodule.c

@@ -5188,7 +5188,7 @@ convert_sched_param(PyObject *param, struct sched_param *res);
 
 static int
 parse_posix_spawn_flags(PyObject *setpgroup, int resetids, PyObject *setsigmask,
-                        PyObject *setsigdef, PyObject *scheduler,
+                        PyObject *setsigdef, PyObject *scheduler, int use_vfork,
                         posix_spawnattr_t *attrp)
 {
     long all_flags = 0;
@@ -5278,6 +5278,16 @@ parse_posix_spawn_flags(PyObject *setpgroup, int resetids, PyObject *setsigmask,
 #endif
     }
 
+    if (use_vfork) {
+#ifdef POSIX_SPAWN_USEVFORK
+        all_flags |= POSIX_SPAWN_SETSCHEDULER;
+#else
+        PyErr_SetString(PyExc_NotImplementedError,
+                "The POSIX_SPAWN_USEVFORK flag is unavailable on this platform");
+        goto fail;
+#endif
+    }
+
     errno = posix_spawnattr_setflags(attrp, all_flags);
     if (errno) {
         posix_error();
@@ -5425,6 +5435,8 @@ os.posix_spawn
         The sigmask to use with the POSIX_SPAWN_SETSIGDEF flag.
     scheduler: object = NULL
         A tuple with the scheduler policy (optional) and parameters.
+    use_vfork: bool(accept={int}) = False
+        If the value is true the POSIX_SPAWN_USEVFORK will be activated.
 
 Execute the program specified by path in a new process.
 [clinic start generated code]*/
@@ -5433,8 +5445,8 @@ static PyObject *
 os_posix_spawn_impl(PyObject *module, path_t *path, PyObject *argv,
                     PyObject *env, PyObject *file_actions,
                     PyObject *setpgroup, int resetids, PyObject *setsigmask,
-                    PyObject *setsigdef, PyObject *scheduler)
-/*[clinic end generated code: output=45dfa4c515d09f2c input=2891c2f1d457e39b]*/
+                    PyObject *setsigdef, PyObject *scheduler, int use_vfork)
+/*[clinic end generated code: output=ed9323af139a50f7 input=9ca9c905ec19bf04]*/
 {
     EXECV_CHAR **argvlist = NULL;
     EXECV_CHAR **envlist = NULL;
@@ -5504,7 +5516,7 @@ os_posix_spawn_impl(PyObject *module, path_t *path, PyObject *argv,
     }
 
     if (parse_posix_spawn_flags(setpgroup, resetids, setsigmask,
-                                setsigdef, scheduler, &attr)) {
+                                setsigdef, scheduler, use_vfork, &attr)) {
         goto exit;
     }
     attrp = &attr;