qemu.tests.virtio_console: New interrupted loopback mode

Currently qemu dies when we try to remove and plug the port couple of
times without delay.

This modification allows to execute x (virtio_console_micro_repeates)
interuptions, where we don't check anything, only do them as fast as
possible. After that we execute normal loop where the transfer is
checked after each interruption.

As the port might not be openable for some time, the guest_worker
supports multiple attemps to open the port. Don't forget to remove
the old /tmp/virtio_console_guest.py* files in order to use the new one.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

qemu/tests/cfg/virtio_console.cfg

@@ -93,10 +93,19 @@
                             virtio_console_buflen = 7
                             virtio_console_debug = normal
                             variants:
+                                - micro:
+                                    # following test's interruptions takes so
+                                    # long that this variant would be similar
+                                    # to the short one
+                                    no suspend, hibernate
+                                    virtio_console_micro_repeats = 60
+                                    virtio_console_no_repeats = 1
+                                    virtio_console_test_time = 10
+                                    virtio_console_intr_time = 0
                                 - short:
                                     virtio_console_no_repeats = 60
-                                    virtio_console_test_time = 0.1
-                                    virtio_console_intr_time = 0
+                                    virtio_console_test_time = 1
+                                    virtio_console_intr_time = 0.5
                                 - long:
                                     virtio_console_no_repeats = 1
                                     virtio_console_test_time = 30

qemu/tests/virtio_console.py

@@ -987,6 +987,15 @@ def run_virtio_console(test, params, env):
             raise error.TestFail("Sender thread died before interruption.")
         if not threads[0].isAlive():
             raise error.TestFail("Receiver thread died before interruption.")
+
+        # 0s interruption without any measurements
+        if params.get('virtio_console_micro_repeats'):
+            error.context("Micro interruptions", logging.info)
+            threads[1].sendidx = acceptable_loss
+            for i in xrange(int(params.get('virtio_console_micro_repeats'))):
+                interruption()
+
+        error.context("Normal interruptions", logging.info)
         try:
             for i in xrange(no_repeats):
                 error.context("Interruption nr. %s" % i)