WIP: gh-114467: Support posix_spawn in subprocess.Popen with cwd != None

Doc/library/os.rst

@@ -5161,11 +5161,18 @@ written in Python, such as a mail server's external command delivery program.
 
       Performs ``os.closerange(fd, INF)``.
 
+   .. data:: POSIX_SPAWN_CHDIR
+
+      (``os.POSIX_SPAWN_CHDIR``, *path*)
+
+      Performs ``os.chdir(path)``.
+
    These tuples correspond to the C library
    :c:func:`!posix_spawn_file_actions_addopen`,
    :c:func:`!posix_spawn_file_actions_addclose`,
-   :c:func:`!posix_spawn_file_actions_adddup2`, and
-   :c:func:`!posix_spawn_file_actions_addclosefrom_np` API calls used to prepare
+   :c:func:`!posix_spawn_file_actions_adddup2`,
+   :c:func:`!posix_spawn_file_actions_addclosefrom_np`, and
+   :c:func:`!posix_spawn_file_actions_addchdir_np` 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
@@ -5212,6 +5219,10 @@ written in Python, such as a mail server's external command delivery program.
       ``os.POSIX_SPAWN_CLOSEFROM`` is available on platforms where
       :c:func:`!posix_spawn_file_actions_addclosefrom_np` exists.
 
+   .. versionchanged:: 3.15
+      ``os.POSIX_SPAWN_CHDIR`` is available on platforms where
+      :c:func:`!posix_spawn_file_actions_addchdir_np` exist.
+
    .. availability:: Unix, not WASI, not Android, not iOS.
 
 .. function:: posix_spawnp(path, argv, env, *, file_actions=None, \

Lib/subprocess.py

@@ -806,6 +806,7 @@ def _can_use_kqueue():
 # These are primarily fail-safe knobs for negatives. A True value does not
 # guarantee the given libc/syscall API will be used.
 _USE_POSIX_SPAWN = _use_posix_spawn()
+_HAVE_POSIX_SPAWN_CHDIR = hasattr(os, 'POSIX_SPAWN_CHDIR')
 _HAVE_POSIX_SPAWN_CLOSEFROM = hasattr(os, 'POSIX_SPAWN_CLOSEFROM')
 
 
@@ -1836,7 +1837,7 @@ def _get_handles(self, stdin, stdout, stderr):
                     errread, errwrite)
 
 
-        def _posix_spawn(self, args, executable, env, restore_signals, close_fds,
+        def _posix_spawn(self, args, executable, env, restore_signals, close_fds, cwd,
                          p2cread, p2cwrite,
                          c2pread, c2pwrite,
                          errread, errwrite):
@@ -1863,6 +1864,9 @@ def _posix_spawn(self, args, executable, env, restore_signals, close_fds,
                 if fd != -1:
                     file_actions.append((os.POSIX_SPAWN_DUP2, fd, fd2))
 
+            if cwd is not None:
+                file_actions.append((os.POSIX_SPAWN_CHDIR, cwd))
+
             if close_fds:
                 file_actions.append((os.POSIX_SPAWN_CLOSEFROM, 3))
 
@@ -1915,7 +1919,7 @@ def _execute_child(self, args, executable, preexec_fn, close_fds,
                     and preexec_fn is None
                     and (not close_fds or _HAVE_POSIX_SPAWN_CLOSEFROM)
                     and not pass_fds
-                    and cwd is None
+                    and (cwd is None or _HAVE_POSIX_SPAWN_CHDIR)
                     and (p2cread == -1 or p2cread > 2)
                     and (c2pwrite == -1 or c2pwrite > 2)
                     and (errwrite == -1 or errwrite > 2)
@@ -1925,7 +1929,8 @@ def _execute_child(self, args, executable, preexec_fn, close_fds,
                     and gids is None
                     and uid is None
                     and umask < 0):
-                self._posix_spawn(args, executable, env, restore_signals, close_fds,
+                self._posix_spawn(args, executable, env, restore_signals,
+                                  close_fds, cwd,
                                   p2cread, p2cwrite,
                                   c2pread, c2pwrite,
                                   errread, errwrite)

Lib/test/test_subprocess.py

@@ -2018,6 +2018,7 @@ def _get_chdir_exception(self):
                       self._nonexistent_dir)
         return desired_exception
 
+    @mock.patch("subprocess._HAVE_POSIX_SPAWN_CHDIR", new=False)
     def test_exception_cwd(self):
         """Test error in the child raised in the parent for a bad cwd."""
         desired_exception = self._get_chdir_exception()

Misc/NEWS.d/next/Library/2026-04-01-15-16-28.gh-issue-114467.g-8r4E.rst

@@ -0,0 +1,3 @@
+The :mod:`subprocess` module can now use the :func:`os.posix_spawn` function
+with ``cwd`` set on platforms where ``posix_spawn_file_actions_addchdir_np``
+is available. Patch by Jakub Kulik.

Modules/posixmodule.c

@@ -7606,6 +7606,9 @@ enum posix_spawn_file_actions_identifier {
 #ifdef HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCLOSEFROM_NP
     ,POSIX_SPAWN_CLOSEFROM
 #endif
+#ifdef HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCHDIR_NP
+    ,POSIX_SPAWN_CHDIR
+#endif
 };
 
 #if defined(HAVE_SCHED_SETPARAM) || defined(HAVE_SCHED_SETSCHEDULER) || defined(POSIX_SPAWN_SETSCHEDULER) || defined(POSIX_SPAWN_SETSCHEDPARAM)
@@ -7757,7 +7760,7 @@ parse_posix_spawn_flags(PyObject *module, const char *func_name, PyObject *setpg
 static int
 parse_file_actions(PyObject *file_actions,
                    posix_spawn_file_actions_t *file_actionsp,
-                   PyObject *temp_buffer)
+                   PyObject *temp_buffer, PyObject* cwd_buffer)
 {
     PyObject *seq;
     PyObject *file_action = NULL;
@@ -7864,6 +7867,29 @@ parse_file_actions(PyObject *file_actions,
                 }
                 break;
             }
+#endif
+#ifdef HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCHDIR_NP
+            case POSIX_SPAWN_CHDIR: {
+                PyObject *path;
+                if (!PyArg_ParseTuple(file_action, "OO&"
+                        ";A chdir file_action tuple must have 2 elements",
+                        &tag_obj, PyUnicode_FSConverter, &path))
+                {
+                    goto fail;
+                }
+                errno = posix_spawn_file_actions_addchdir_np(file_actionsp,
+                        PyBytes_AS_STRING(path));
+                if (errno) {
+                    posix_error();
+                    Py_DECREF(path);
+                    goto fail;
+                }
+                if (PyList_Append(cwd_buffer, path)) {
+                    Py_DECREF(path);
+                    goto fail;
+                }
+                break;
+            }
 #endif
             default: {
                 PyErr_SetString(PyExc_TypeError,
@@ -7901,6 +7927,7 @@ py_posix_spawn(int use_posix_spawnp, PyObject *module, path_t *path, PyObject *a
     Py_ssize_t argc, envc;
     PyObject *result = NULL;
     PyObject *temp_buffer = NULL;
+    PyObject *cwd_buffer = NULL;
     pid_t pid;
     int err_code;
 
@@ -7972,7 +7999,13 @@ py_posix_spawn(int use_posix_spawnp, PyObject *module, path_t *path, PyObject *a
         if (!temp_buffer) {
             goto exit;
         }
-        if (parse_file_actions(file_actions, &file_actions_buf, temp_buffer)) {
+        /* Use a list to capture all directories passed via POSIX_SPAWN_CHDIR
+         * action for potential exception creation below. */
+        cwd_buffer = PyList_New(0);
+        if (!cwd_buffer) {
+            goto exit;
+        }
+        if (parse_file_actions(file_actions, &file_actions_buf, temp_buffer, cwd_buffer)) {
             goto exit;
         }
         file_actionsp = &file_actions_buf;
@@ -8004,6 +8037,41 @@ py_posix_spawn(int use_posix_spawnp, PyObject *module, path_t *path, PyObject *a
 
     if (err_code) {
         errno = err_code;
+#ifdef HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCHDIR_NP
+        Py_ssize_t cwd_size;
+        if (errno == ENOENT && cwd_buffer && (cwd_size = PyList_GET_SIZE(cwd_buffer))) {
+            /* ENOENT can occur when either the path of the executable or any of
+             * the cwds given via file_actions doesn't exist. Since it's not
+             * possible to determine which of those paths caused the problem,
+             * we return an exception with all of those. */
+
+            if (cwd_size == 1) {
+                PyObject *cwd = PyList_GET_ITEM(cwd_buffer, 0);
+                PyErr_Format(PyExc_FileNotFoundError, "Either '%S' or '%s' doesn't exist.",
+                         path->object, PyBytes_AS_STRING(cwd));
+            } else {
+                /* Multiple POSIX_SPAWN_CHDIR actions were used in a single
+                 * spawn. In this case, we have to build the expection message
+                 * from all possibly missing paths. */
+                PyObject *separator = PyBytes_FromString(", ");
+                if (!separator) {
+                    goto exit;
+                }
+
+                PyObject *joined = PyBytes_Join(separator, cwd_buffer);
+                Py_DECREF(separator);
+                if (!joined) {
+                    goto exit;
+                }
+                PyErr_Format(PyExc_FileNotFoundError,
+                             "Either '%S' or one of (%s) doesn't exist.",
+                             path->object, PyBytes_AS_STRING(joined));
+
+                Py_DECREF(joined);
+            }
+            goto exit;
+        }
+#endif
         PyErr_SetFromErrnoWithFilenameObject(PyExc_OSError, path->object);
         goto exit;
     }
@@ -8025,6 +8093,7 @@ py_posix_spawn(int use_posix_spawnp, PyObject *module, path_t *path, PyObject *a
     if (argvlist) {
         free_string_array(argvlist, argc);
     }
+    Py_XDECREF(cwd_buffer);
     Py_XDECREF(temp_buffer);
     return result;
 }
@@ -18150,6 +18219,9 @@ all_ins(PyObject *m)
 #ifdef HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCLOSEFROM_NP
     if (PyModule_AddIntMacro(m, POSIX_SPAWN_CLOSEFROM)) return -1;
 #endif
+#ifdef HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCHDIR_NP
+    if (PyModule_AddIntMacro(m, POSIX_SPAWN_CHDIR)) return -1;
+#endif
 #endif
 
 #if defined(HAVE_SPAWNV) || defined (HAVE_RTPSPAWN)

configure.ac

@@ -5371,7 +5371,7 @@ fi
 # header definition prevents usage - autoconf doesn't use the headers), or
 # raise an error if used at runtime. Force these symbols off.
 if test "$ac_sys_system" != "iOS" ; then
-  AC_CHECK_FUNCS([getentropy getgroups system])
+  AC_CHECK_FUNCS([getentropy getgroups posix_spawn_file_actions_addchdir_np system])
 fi
 
 AC_CHECK_DECL([dirfd],

pyconfig.h.in

@@ -975,6 +975,10 @@
 /* Define to 1 if you have the 'posix_spawnp' function. */
 #undef HAVE_POSIX_SPAWNP
 
+/* Define to 1 if you have the 'posix_spawn_file_actions_addchdir_np'
+   function. */
+#undef HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCHDIR_NP
+
 /* Define to 1 if you have the 'posix_spawn_file_actions_addclosefrom_np'
    function. */
 #undef HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCLOSEFROM_NP