bpo-38692: Add os.pidfd_open. (GH-17063)

Author: benjaminp

Doc/library/os.rst

@@ -3539,6 +3539,19 @@ written in Python, such as a mail server's external command delivery program.
    .. availability:: Unix.
 
 
+.. function:: pidfd_open(pid, flags=0)
+
+   Return a file descriptor referring to the process *pid*.  This descriptor can
+   be used to perform process management without races and signals.  The *flags*
+   argument is provided for future extensions; no flag values are currently
+   defined.
+
+   See the :manpage:`pidfd_open(2)` man page for more details.
+
+   .. availability:: Linux 5.3+
+   .. versionadded:: 3.9
+
+
 .. function:: plock(op)
 
    Lock program segments into memory.  The value of *op* (defined in

Doc/whatsnew/3.9.rst

@@ -150,6 +150,9 @@ os
 Added :data:`~os.CLD_KILLED` and :data:`~os.CLD_STOPPED` for :attr:`si_code`.
 (Contributed by Dong-hee Na in :issue:`38493`.)
 
+Exposed the Linux-specific :func:`os.pidfd_open` for process management with
+file descriptors. (:issue:`38692`)
+
 threading
 ---------
 

Lib/test/test_posix.py

@@ -1470,6 +1470,15 @@ def test_path_with_null_byte(self):
         open(fn, 'wb').close()
         self.assertRaises(ValueError, os.stat, fn_with_NUL)
 
+    @unittest.skipUnless(hasattr(os, "pidfd_open"), "pidfd_open unavailable")
+    def test_pidfd_open(self):
+        with self.assertRaises(OSError) as cm:
+            os.pidfd_open(-1)
+        if cm.exception.errno == errno.ENOSYS:
+            self.skipTest("system does not support pidfd_open")
+        self.assertEqual(cm.exception.errno, errno.EINVAL)
+        os.close(os.pidfd_open(os.getpid(), 0))
+
 class PosixGroupsTester(unittest.TestCase):
 
     def setUp(self):

Misc/NEWS.d/next/Library/2019-11-05-07-18-24.bpo-38692.UpatA7.rst

@@ -0,0 +1 @@
+Expose the Linux ``pidfd_open`` syscall as :func:`os.pidfd_open`.

Modules/clinic/posixmodule.c.h

@@ -7861,6 +7861,30 @@ os_wait_impl(PyObject *module)
 }
 #endif /* HAVE_WAIT */
 
+#if defined(__linux__) && defined(__NR_pidfd_open)
+/*[clinic input]
+os.pidfd_open
+  pid: pid_t
+  flags: unsigned_int = 0
+
+Return a file descriptor referring to the process *pid*.
+
+The descriptor can be used to perform process management without races and
+signals.
+[clinic start generated code]*/
+
+static PyObject *
+os_pidfd_open_impl(PyObject *module, pid_t pid, unsigned int flags)
+/*[clinic end generated code: output=5c7252698947dc41 input=c3fd99ce947ccfef]*/
+{
+    int fd = syscall(__NR_pidfd_open, pid, flags);
+    if (fd < 0) {
+        return posix_error();
+    }
+    return PyLong_FromLong(fd);
+}
+#endif
+
 
 #if defined(HAVE_READLINK) || defined(MS_WINDOWS)
 /*[clinic input]
@@ -13671,6 +13695,7 @@ static PyMethodDef posix_methods[] = {
     OS_WAIT4_METHODDEF
     OS_WAITID_METHODDEF
     OS_WAITPID_METHODDEF
+    OS_PIDFD_OPEN_METHODDEF
     OS_GETSID_METHODDEF
     OS_SETSID_METHODDEF
     OS_SETPGID_METHODDEF