Re: [PATCH] docs/system/s390x: Improve the 3270 documentation

[Thomas Huth <thuth@redhat.com>]

On 10/07/2020 12.55, Cornelia Huck wrote:
> On Thu,  9 Jul 2020 18:04:39 +0200
> Thomas Huth <thuth@redhat.com> wrote:
> 
>> There is some additional information about the 3270 support in our
>> Wiki at https://wiki.qemu.org/Features/3270 - so let's include this
>> information into the main documentation now to have one single
>> source of information (the Wiki page could later be removed).
> 
> No objection; but what should our general policy with regard to wiki
> pages vs. documentation be? The 3270 support is pretty much static, but
> e.g. for vfio-ccw, we use the wiki page as a place where we track
> things that should be worked on etc.

I think that docs which are "done" should go into the git repo. If they
are rather still work-in-progress and change very often, or relate to a
feature that has not been merged yet, the wiki is likely the better place.

> (Related: What is the scope of our QEMU documentation? Is a libvirt XML
> snippet on topic? Kernel configuration options (as in here)?)

As long as the focus is still on QEMU, I think it is fine. If the
information is only about libvirt or the kernel, that documentation
should maybe rather be added to libvirt.org or linux-kvm.org instead.

>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>> ---
>>  docs/system/s390x/3270.rst | 43 ++++++++++++++++++++++++++++++++------
>>  1 file changed, 37 insertions(+), 6 deletions(-)
>>
>> diff --git a/docs/system/s390x/3270.rst b/docs/system/s390x/3270.rst
>> index 1774cdcadf..80350264d7 100644
>> --- a/docs/system/s390x/3270.rst
>> +++ b/docs/system/s390x/3270.rst
>> @@ -1,9 +1,15 @@
>>  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.
>> +The 3270 is the classic 'green-screen' console of the mainframes (see the
>> +`IBM 3270 Wikipedia article <https://en.wikipedia.org/wiki/IBM_3270>`__).
>> +
>> +The 3270 data stream is not implemented within QEMU; the device only provides
>> +TN3270 (a telnet extension; see `RFC 854 <https://tools.ietf.org/html/rfc854>`__
>> +and `RFC 1576 <https://tools.ietf.org/html/rfc1576>`__) and leaves the heavy
>> +lifting to 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
>> @@ -12,10 +18,14 @@ to actually be able to use it, attach the ``x3270`` emulator to the chardev.
>>  Example configuration
>>  ---------------------
>>  
>> +* Make sure that 3270 support is enabled in the guest's kernel. You need
>> +  ``CONFIG_TN3270`` and at least one of ``CONFIG_TN3270_TTY`` (for additional
>> +  ttys) or ``CONFIG_TN3270_CONSOLE`` (for a 3270 console).
>> +
>>  * 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
>> +   -chardev socket,id=ch0,host=0.0.0.0,port=2300,nowait,server,tn3270
>> +   -device x-terminal3270,chardev=ch0,devno=fe.0.000a,id=terminal0
> 
> Any reason why you changed this?

The lines were too long - Firefox displayed this example with a
horizontal scrollbar, even if I resized the browser window large enough.
With my change, it shows up nicely without scrollbar.

>>  
>>  * Start the guest. In the guest, use ``chccwdev -e 0.0.000a`` to enable
>>    the device.
>> @@ -29,4 +39,25 @@ Example configuration
>>  
>>      systemctl start serial-getty@3270-tty1.service
>>  
>> -This should get you an addtional tty for logging into the guest.
>> +  This should get you an addtional tty for logging into the guest.
>> +
>> +* If you want to use the 3270 device as the kernel console instead of an
>> +  additional tty, you can also append ``conmode=3270 condev=000a`` to the
>> +  guest's kernel command line. The kernel then should use the 3270 as
>> +  console after the next boot.
>> +
>> +Restrictions
>> +------------
>> +
>> +3270 support is still experimental. In particular:
> 
> s/still experimental/very basic/
> 
> I don't think there's much progress on the horizon; let's not give
> people false hope :)
> 
>> +
>> +* Only one 3270 device is supported.
>> +
>> +* It has only been tested with Linux guests and the x3270 emulator.
>> +
>> +* TLS/SSL is not yet supported.
> 
> s/yet //
> 
>> +
>> +* Resizing on reattach is not yet supported.
> 
> s/yet //
> 
>> +
>> +* Multiple commands in one inbound buffer (for example, when the reset key
>> +  is pressed while the network is slow) are not yet supported.
> 
> s/yet //
> 

I'll fix these in v2.

Thanks for the review!

 Thomas