docs/s390x: document 3270

3270 devices

============

QEMU supports connecting an external 3270 terminal emulator (such as

``x3270``) to make a single 3270 device available to a guest. Note that this

supports basic features only.

To provide a 3270 device to a guest, create a ``x-terminal3270`` linked to

a ``tn3270`` chardev. The guest will see a 3270 channel device. In order

to actually be able to use it, attach the ``x3270`` emulator to the chardev.

Example configuration

---------------------

* Add a ``tn3270`` chardev and a ``x-terminal3270`` to the QEMU command line::

    -chardev socket,id=char_0,host=0.0.0.0,port=2300,nowait,server,tn3270

    -device x-terminal3270,chardev=char_0,devno=fe.0.000a,id=terminal_0

* Start the guest. In the guest, use ``chccwdev -e 0.0.000a`` to enable

  the device.

* On the host, start the ``x3270`` emulator::

    x3270 <host>:2300

* In the guest, locate the 3270 device node under ``/dev/3270/`` (say,

  ``tty1``) and start a getty on it::

    systemctl start serial-getty@3270-tty1.service

This should get you an addtional tty for logging into the guest.

.. toctree::

   s390x/vfio-ap

   s390x/css

   s390x/3270

Architectural features

======================