[Qemu-devel] handling SIGWINCH with qemu -nographic

[Qemu-devel] handling SIGWINCH with qemu -nographic

[Jeff Carr]

Has anyone looked into finding a way to pass SIGWINCH through to the
guest? I started looking at linux-user/signal.c.

For those that might not be familiar with SIGWINCH, supporting it
would allow qemu -nographic to tell when the terminal is a different
size than 80x24.

Re: [Qemu-devel] handling SIGWINCH with qemu -nographic

[Paul Brook]

On Tuesday 16 October 2007, Jeff Carr wrote:
> Has anyone looked into finding a way to pass SIGWINCH through to the
> guest? I started looking at linux-user/signal.c.
>
> For those that might not be familiar with SIGWINCH, supporting it
> would allow qemu -nographic to tell when the terminal is a different
> size than 80x24.

qemu emulates a real machine. Signals are an operating system concept, so your 
question makes no sense.  Configure your guest OS exactly the same way you 
would a real machine with a serial console.

The linux-user code is for the userspace emulation. You're obviously using the 
full system emulation.

Paul

Re: [Qemu-devel] handling SIGWINCH with qemu -nographic

[Stuart Brady]

On Mon, Oct 15, 2007 at 06:15:29PM -0700, Jeff Carr wrote:
> For those that might not be familiar with SIGWINCH, supporting it
> would allow qemu -nographic to tell when the terminal is a different
> size than 80x24.

That would need support on the remote side (the getty) as well as on the 
terminal (minicom/tip/qemu -nographic/whatever).

While this would be a nice feature (and support for propagating the 
TERM, LANG and LC_* variables might be nice, too), I'm doubtful as to 
whether this will ever happen.
-- 
Stuart Brady

Re: [Qemu-devel] handling SIGWINCH with qemu -nographic

[Jeff Carr]

On 10/15/07 19:32, Paul Brook wrote:

> qemu emulates a real machine. Signals are an operating system concept, so your
> question makes no sense.  Configure your guest OS exactly the same way you 
> would a real machine with a serial console.

OK. I thought there might be a way.

> The linux-user code is for the userspace emulation. You're obviously using the 
> full system emulation.

It seemed that's where the handler would have to go. I don't know if
there is some way to pass that through a serial device. I wasn't sure
if it would require some custom qemu serial driver for the guest.

Re: [Qemu-devel] handling SIGWINCH with qemu -nographic

[Stefan Weil]

Jeff Carr schrieb:
> On 10/15/07 19:32, Paul Brook wrote:
>
>> qemu emulates a real machine. Signals are an operating system
>> concept, so your
>> question makes no sense. Configure your guest OS exactly the same way
>> you
>> would a real machine with a serial console.
>
> OK. I thought there might be a way.
I think your question is quite reasonable. Imagine a Linux host
running X Windows and a terminal like xterm or kconsole.
Then run a program like "top" or "less" in this terminal.
When a user changes the size of the console window, top, less
and other console applications get notified of this change by SIGWINCH.

Now run a similar program using QEMU's user mode emulation.
Why should it not be possible to get SIGWINCH in QEMU and
pass it on to the program in user mode emulation, so it can
behave like a native Linux application and change its appearance?

I don't think that implementing this is very difficult, so it will be
done.


Regards
Stefan

Re: [Qemu-devel] handling SIGWINCH with qemu -nographic

[Paul Brook]

> I think your question is quite reasonable. Imagine a Linux host
> running X Windows and a terminal like xterm or kconsole.
> Then run a program like "top" or "less" in this terminal.
> When a user changes the size of the console window, top, less
> and other console applications get notified of this change by SIGWINCH.
>
> Now run a similar program using QEMU's user mode emulation.
> Why should it not be possible to get SIGWINCH in QEMU and
> pass it on to the program in user mode emulation, so it can
> behave like a native Linux application and change its appearance?
>
> I don't think that implementing this is very difficult, so it will be
> done.

Try doing the same thing with a real machine connected via a serial port.
It won't work.

The difference is that for local applications (and remote terminals via telnet 
or ssh) you have OOB mechanisms to transmit event data (e.g. terminal size). 
A UART only gives you a simple serial connection. If you want things like 
terminal resizing to work you need to run some more complicated protocol over 
the serial link, with appropriate tty emulation on either end.

Paul

Re: [Qemu-devel] handling SIGWINCH with qemu -nographic

[Rob Landley]

On Monday 15 October 2007 8:15:29 pm Jeff Carr wrote:
> Has anyone looked into finding a way to pass SIGWINCH through to the
> guest? I started looking at linux-user/signal.c.
>
> For those that might not be familiar with SIGWINCH, supporting it
> would allow qemu -nographic to tell when the terminal is a different
> size than 80x24.

The problem is a serial port is essentially a pipe.  You don't get tty 
information about the terminal plugged into the other side, because that's a 
separate machine on the other side of a piece of hardware which doesn't pass 
through that info.  (What _is_ the width and height of a modem?)

Have your program send an ansi probe sequence:

echo -e "\e[s\e[999C\e[999B\e[6n\e[u"

Then parse the return string, which should look something like escape left 
bracket 25 semicolon 80 capital R, and use it to set $LINES=25 and 
$COLUMNS=80.

Any modern terminal program should handle that and spit back a result telling 
you big the tty is (although it doesn't tell you when it _changes_, you have 
to re-probe).  Yes, it's in-band signalling but over a serial connection 
that's all you've got.

Rob
-- 
"One of my most productive days was throwing away 1000 lines of code."
  - Ken Thompson.

Re: [Qemu-devel] handling SIGWINCH with qemu -nographic

[Rob Landley]

On Tuesday 16 October 2007 3:51:29 pm Stefan Weil wrote:
> Jeff Carr schrieb:
> > On 10/15/07 19:32, Paul Brook wrote:
> >> qemu emulates a real machine. Signals are an operating system
> >> concept, so your
> >> question makes no sense. Configure your guest OS exactly the same way
> >> you
> >> would a real machine with a serial console.
> >
> > OK. I thought there might be a way.
>
> I think your question is quite reasonable. Imagine a Linux host
> running X Windows and a terminal like xterm or kconsole.

This is why ssh was invented.  That passes through terminal information just 
fine.  QEMU does have a virtual network...

> Then run a program like "top" or "less" in this terminal.
> When a user changes the size of the console window, top, less
> and other console applications get notified of this change by SIGWINCH.

You can also set the environment variables COLUMNS and LINES to the 
appropriate values.  Most things will parse that and use it if the tty info 
isn't available.

Rob
-- 
"One of my most productive days was throwing away 1000 lines of code."
  - Ken Thompson.