diff -r dee33603a5fa Lib/test/test_os.py
--- a/Lib/test/test_os.py	Fri Jan 03 03:26:47 2014 +0100
+++ b/Lib/test/test_os.py	Fri Jan 03 12:20:04 2014 +0100
@@ -1267,6 +1267,11 @@ class TestInvalidFD(unittest.TestCase):
     def test_read(self):
         self.check(os.read, 1)
 
+    @unittest.skipUnless(hasattr(os, 'readv'), 'test needs os.readv()')
+    def test_read(self):
+        buf = bytearray(10)
+        self.check(os.readv, [buf])
+
     @unittest.skipUnless(hasattr(os, 'tcsetpgrp'), 'test needs os.tcsetpgrp()')
     def test_tcsetpgrpt(self):
         self.check(os.tcsetpgrp, 0)
@@ -1275,6 +1280,10 @@ class TestInvalidFD(unittest.TestCase):
     def test_write(self):
         self.check(os.write, b" ")
 
+    @unittest.skipUnless(hasattr(os, 'writev'), 'test needs os.writev()')
+    def test_write(self):
+        self.check(os.writev, [b'abc'])
+
 
 class LinkTests(unittest.TestCase):
     def setUp(self):
diff -r dee33603a5fa Lib/test/test_posix.py
--- a/Lib/test/test_posix.py	Fri Jan 03 03:26:47 2014 +0100
+++ b/Lib/test/test_posix.py	Fri Jan 03 12:20:04 2014 +0100
@@ -283,9 +283,14 @@ class PosixTester(unittest.TestCase):
     def test_writev(self):
         fd = os.open(support.TESTFN, os.O_RDWR | os.O_CREAT)
         try:
-            os.writev(fd, (b'test1', b'tt2', b't3'))
+            n = os.writev(fd, (b'test1', b'tt2', b't3'))
+            self.assertEqual(n, 10)
+
             os.lseek(fd, 0, os.SEEK_SET)
             self.assertEqual(b'test1tt2t3', posix.read(fd, 10))
+
+            # Issue #20113: empty list of buffers should not crash
+            self.assertEqual(posix.writev(fd, []), 0)
         finally:
             os.close(fd)
 
@@ -298,6 +303,9 @@ class PosixTester(unittest.TestCase):
             buf = [bytearray(i) for i in [5, 3, 2]]
             self.assertEqual(posix.readv(fd, buf), 10)
             self.assertEqual([b'test1', b'tt2', b't3'], [bytes(i) for i in buf])
+
+            # Issue #20113: empty list of buffers should not crash
+            self.assertEqual(posix.readv(fd, []), 0)
         finally:
             os.close(fd)
 
diff -r dee33603a5fa Modules/posixmodule.c
--- a/Modules/posixmodule.c	Fri Jan 03 03:26:47 2014 +0100
+++ b/Modules/posixmodule.c	Fri Jan 03 12:20:04 2014 +0100
@@ -8011,14 +8011,14 @@ iov_setup(struct iovec **iov, Py_buffer 
     *iov = PyMem_New(struct iovec, cnt);
     if (*iov == NULL) {
         PyErr_NoMemory();
-        return total;
+        return -1;
     }
 
     *buf = PyMem_New(Py_buffer, cnt);
     if (*buf == NULL) {
         PyMem_Del(*iov);
         PyErr_NoMemory();
-        return total;
+        return -1;
     }
 
     for (i = 0; i < cnt; i++) {
@@ -8043,7 +8043,7 @@ fail:
         PyBuffer_Release(&(*buf)[j]);
     }
     PyMem_Del(*buf);
-    return 0;
+    return -1;
 }
 
 static void
@@ -8083,7 +8083,7 @@ posix_readv(PyObject *self, PyObject *ar
     }
     cnt = PySequence_Size(seq);
 
-    if (!iov_setup(&iov, &buf, seq, cnt, PyBUF_WRITABLE))
+    if (iov_setup(&iov, &buf, seq, cnt, PyBUF_WRITABLE) < 0)
         return NULL;
 
     Py_BEGIN_ALLOW_THREADS
@@ -8091,6 +8091,9 @@ posix_readv(PyObject *self, PyObject *ar
     Py_END_ALLOW_THREADS
 
     iov_cleanup(iov, buf, cnt);
+    if (n < 0)
+        return posix_error();
+
     return PyLong_FromSsize_t(n);
 }
 #endif
@@ -8216,8 +8219,8 @@ posix_sendfile(PyObject *self, PyObject 
             Py_ssize_t i = 0; /* Avoid uninitialized warning */
             sf.hdr_cnt = PySequence_Size(headers);
             if (sf.hdr_cnt > 0 &&
-                !(i = iov_setup(&(sf.headers), &hbuf,
-                                headers, sf.hdr_cnt, PyBUF_SIMPLE)))
+                (i = iov_setup(&(sf.headers), &hbuf,
+                                headers, sf.hdr_cnt, PyBUF_SIMPLE)) < 0)
                 return NULL;
 #ifdef __APPLE__
             sbytes += i;
@@ -8233,8 +8236,8 @@ posix_sendfile(PyObject *self, PyObject 
             Py_ssize_t i = 0; /* Avoid uninitialized warning */
             sf.trl_cnt = PySequence_Size(trailers);
             if (sf.trl_cnt > 0 &&
-                !(i = iov_setup(&(sf.trailers), &tbuf,
-                                trailers, sf.trl_cnt, PyBUF_SIMPLE)))
+                (i = iov_setup(&(sf.trailers), &tbuf,
+                                trailers, sf.trl_cnt, PyBUF_SIMPLE)) < 0)
                 return NULL;
 #ifdef __APPLE__
             sbytes += i;
@@ -8475,7 +8478,7 @@ posix_writev(PyObject *self, PyObject *a
     }
     cnt = PySequence_Size(seq);
 
-    if (!iov_setup(&iov, &buf, seq, cnt, PyBUF_SIMPLE)) {
+    if (iov_setup(&iov, &buf, seq, cnt, PyBUF_SIMPLE) < 0) {
         return NULL;
     }
 
@@ -8484,6 +8487,9 @@ posix_writev(PyObject *self, PyObject *a
     Py_END_ALLOW_THREADS
 
     iov_cleanup(iov, buf, cnt);
+    if (res < 0)
+        return posix_error();
+
     return PyLong_FromSsize_t(res);
 }
 #endif