xref: /openbmc/qemu/docs/system/s390x/3270.rst (revision 05caa062)
13270 devices
2============
3
4The 3270 is the classic 'green-screen' console of the mainframes (see the
5`IBM 3270 Wikipedia article <https://en.wikipedia.org/wiki/IBM_3270>`__).
6
7The 3270 data stream is not implemented within QEMU; the device only provides
8TN3270 (a telnet extension; see `RFC 854 <https://tools.ietf.org/html/rfc854>`__
9and `RFC 1576 <https://tools.ietf.org/html/rfc1576>`__) and leaves the heavy
10lifting to an external 3270 terminal emulator (such as ``x3270``) to make a
11single 3270 device available to a guest. Note that this supports basic
12features only.
13
14To provide a 3270 device to a guest, create a ``x-terminal3270`` linked to
15a ``tn3270`` chardev. The guest will see a 3270 channel device. In order
16to actually be able to use it, attach the ``x3270`` emulator to the chardev.
17
18Example configuration
19---------------------
20
21* Make sure that 3270 support is enabled in the guest's Linux kernel. You need
22  ``CONFIG_TN3270`` and at least one of ``CONFIG_TN3270_TTY`` (for additional
23  ttys) or ``CONFIG_TN3270_CONSOLE`` (for a 3270 console).
24
25* Add a ``tn3270`` chardev and a ``x-terminal3270`` to the QEMU command line::
26
27   -chardev socket,id=ch0,host=0.0.0.0,port=2300,wait=off,server=on,tn3270=on
28   -device x-terminal3270,chardev=ch0,devno=fe.0.000a,id=terminal0
29
30* Start the guest. In the guest, use ``chccwdev -e 0.0.000a`` to enable
31  the device.
32
33* On the host, start the ``x3270`` emulator::
34
35    x3270 <host>:2300
36
37* In the guest, locate the 3270 device node under ``/dev/3270/`` (say,
38  ``tty1``) and start a getty on it::
39
40    systemctl start serial-getty@3270-tty1.service
41
42  This should get you an additional tty for logging into the guest.
43
44* If you want to use the 3270 device as the Linux kernel console instead of
45  an additional tty, you can also append ``conmode=3270 condev=000a`` to
46  the guest's kernel command line. The kernel then should use the 3270 as
47  console after the next boot.
48
49Restrictions
50------------
51
523270 support is very basic. In particular:
53
54* Only one 3270 device is supported.
55
56* It has only been tested with Linux guests and the x3270 emulator.
57
58* TLS/SSL is not supported.
59
60* Resizing on reattach is not supported.
61
62* Multiple commands in one inbound buffer (for example, when the reset key
63  is pressed while the network is slow) are not supported.
64