induce throttling by opening chardev but not reading data from it

Signed-off-by: NMicky Yun Chan <michan@redhat.com>

qemu/tests/cfg/virtio_serial_throttling.cfg

+- virtio_serial_throttling:
+    type = virtio_serial_throttling
+    serials += ' vs1 '
+    serial_type_vs1 = virtserialport
+    chardev_backend_vs1 = unix_socket

qemu/tests/virtio_serial_throttling.py

+import logging
+
+from virttest import error_context, env_process
+from virttest.utils_virtio_port import VirtioPortTest
+
+
+@error_context.context_aware
+def run(test, params, env):
+    """
+    Induce throttling by opening chardev but not reading data from it:
+    1) Start guest with virtio-serial with unix option
+    2) On the host, open the chardev but don't read from it
+    3) In the guest, write to the virtio-serial port.
+    4) transfer data from host to guest but do not read in guest
+    5) repeat step 1 to 4 with tcp option.
+    :param test: QEMU test object
+    :param params: Dictionary with the test parameters
+    :param env: Dictionary with test environment.
+    """
+
+    @error_context.context_aware
+    def send_data_from_guest_to_host():
+        session = vm.wait_for_login()
+        port.open()
+        error_context.context("send data from guest to host", logging.info)
+        if params['os_type'] == 'windows':
+            vport_name = '\\\\.\\Global\\' + port.name
+            cmd = 'dd if=/dev/zero of=%s bs=1024 count=1' % vport_name
+        else:
+            cmd = 'dd if=/dev/zero of=/dev/virtio-ports/%s bs=1024 count=1' % port.name
+        session.cmd(cmd)
+        session.close()
+
+    @error_context.context_aware
+    def send_data_from_host_to_guest():
+        port.open()
+        error_context.context("send data from host to guest", logging.info)
+        data = 'Hello world \n' * 100
+        data = data.encode()
+        port.sock.send(data)
+        guest_worker.cmd("virt.open('%s')" % port.name)
+
+    serial_id = params.objects('serials')[-1]
+    try:
+        virtio_test = VirtioPortTest(test, env, params)
+        (vm, guest_worker, port) = virtio_test.get_vm_with_single_port()
+        vm.verify_alive()
+        send_data_from_guest_to_host()
+        send_data_from_host_to_guest()
+        vm.verify_alive()
+    finally:
+        virtio_test.cleanup()
+    vm.destroy()
+    params['chardev_backend_%s' % serial_id] = 'tcp_socket'
+    vm_name = params['main_vm']
+    env_process.preprocess_vm(test, params, env, vm_name)
+    try:
+        virtio_test = VirtioPortTest(test, env, params)
+        (vm, guest_worker, port) = virtio_test.get_vm_with_single_port()
+        vm.verify_alive()
+        send_data_from_guest_to_host()
+        send_data_from_host_to_guest()
+        vm.verify_alive()
+    finally:
+        virtio_test.cleanup()