iotests: Explicitly bequeath FDs in Python

Python 3.4 introduced the inheritable attribute for FDs.  At the same
time, it changed the default so that all FDs are not inheritable by
default, that only inheritable FDs are inherited to subprocesses, and
only if close_fds is explicitly set to False.

Adhere to this by setting close_fds to False when working with
subprocesses that may want to inherit FDs, and by trying to
set_inheritable() on FDs that we do want to bequeath to them.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Message-Id: <20181022135307.14398-7-mreitz@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

scripts/qemu.py

@@ -148,11 +148,19 @@ class QEMUMachine(object):
         if opts:
             options.append(opts)
 
+        # This did not exist before 3.4, but since then it is
+        # mandatory for our purpose
+        if hasattr(os, 'set_inheritable'):
+            os.set_inheritable(fd, True)
+
         self._args.append('-add-fd')
         self._args.append(','.join(options))
         return self
 
-    def send_fd_scm(self, fd_file_path):
+    # Exactly one of fd and file_path must be given.
+    # (If it is file_path, the helper will open that file and pass its
+    # own fd)
+    def send_fd_scm(self, fd=None, file_path=None):
         # In iotest.py, the qmp should always use unix socket.
         assert self._qmp.is_scm_available()
         if self._socket_scm_helper is None:
@@ -160,12 +168,27 @@ class QEMUMachine(object):
         if not os.path.exists(self._socket_scm_helper):
             raise QEMUMachineError("%s does not exist" %
                                    self._socket_scm_helper)
+
+        # This did not exist before 3.4, but since then it is
+        # mandatory for our purpose
+        if hasattr(os, 'set_inheritable'):
+            os.set_inheritable(self._qmp.get_sock_fd(), True)
+            if fd is not None:
+                os.set_inheritable(fd, True)
+
         fd_param = ["%s" % self._socket_scm_helper,
-                    "%d" % self._qmp.get_sock_fd(),
+                    "%d" % self._qmp.get_sock_fd()]
-                    "%s" % fd_file_path]
+
+        if file_path is not None:
+            assert fd is None
+            fd_param.append(file_path)
+        else:
+            assert fd is not None
+            fd_param.append(str(fd))
+
         devnull = open(os.path.devnull, 'rb')
         proc = subprocess.Popen(fd_param, stdin=devnull, stdout=subprocess.PIPE,
-                                stderr=subprocess.STDOUT)
+                                stderr=subprocess.STDOUT, close_fds=False)
         output = proc.communicate()[0]
         if output:
             LOG.debug(output)
@@ -286,7 +309,8 @@ class QEMUMachine(object):
                                        stdin=devnull,
                                        stdout=self._qemu_log_file,
                                        stderr=subprocess.STDOUT,
-                                       shell=False)
+                                       shell=False,
+                                       close_fds=False)
         self._post_launch()
 
     def wait(self):

tests/qemu-iotests/045

@@ -140,7 +140,7 @@ class TestSCMFd(iotests.QMPTestCase):
         os.remove(image0)
 
     def _send_fd_by_SCM(self):
-        ret = self.vm.send_fd_scm(image0)
+        ret = self.vm.send_fd_scm(file_path=image0)
         self.assertEqual(ret, 0, 'Failed to send fd with UNIX SCM')
 
     def test_add_fd(self):

tests/qemu-iotests/147

@@ -229,7 +229,7 @@ class BuiltinNBD(NBDBlockdevAddBase):
         sockfd = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
         sockfd.connect(unix_socket)
 
-        result = self.vm.send_fd_scm(str(sockfd.fileno()))
+        result = self.vm.send_fd_scm(fd=sockfd.fileno())
         self.assertEqual(result, 0, 'Failed to send socket FD')
 
         result = self.vm.qmp('getfd', fdname='nbd-fifo')