runner: Kill a program under test by time-out

If a program under test get frozen, the test should finish and report about its
failure.
In such cases the runner waits for 10 minutes until the program ends its
execution. After this time-out the program will be terminated and the test will
be marked as failed.

For current limitation of test image size to 10 MB as a maximum an execution of
each command takes about several seconds in general, so 10 minutes is enough to
discriminate freeze, but not drastically increase an overall test duration.

Signed-off-by: Maria Kustova <maria.k@catit.be>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

tests/image-fuzzer/runner.py

@@ -65,14 +65,35 @@ def run_app(fd, q_args):
     """Start an application with specified arguments and return its exit code
     or kill signal depending on the result of execution.
     """
+
+    class Alarm(Exception):
+        """Exception for signal.alarm events."""
+        pass
+
+    def handler(*arg):
+        """Notify that an alarm event occurred."""
+        raise Alarm
+
+    signal.signal(signal.SIGALRM, handler)
+    signal.alarm(600)
+    term_signal = signal.SIGKILL
     devnull = open('/dev/null', 'r+')
     process = subprocess.Popen(q_args, stdin=devnull,
                                stdout=subprocess.PIPE,
                                stderr=subprocess.PIPE)
-    out, err = process.communicate()
-    fd.write(out)
-    fd.write(err)
-    return process.returncode
+    try:
+        out, err = process.communicate()
+        signal.alarm(0)
+        fd.write(out)
+        fd.write(err)
+        fd.flush()
+        return process.returncode
+
+    except Alarm:
+        os.kill(process.pid, term_signal)
+        fd.write('The command was terminated by timeout.\n')
+        fd.flush()
+        return -term_signal
 
 
 class TestException(Exception):