[Qemu-devel] Greetings qemu folks

[Qemu-devel] Greetings qemu folks

[Toe Dev]

I am new in QEMU developing and I have general questions about QEMU source
code as I could not find any guidelines about it.

1) I have no success running qemu in nographic mode.
   The internet says using chardev driver to redirect kernel output to host
OS...
   what is the right way to do that?

2) My main target is to output a lot of this to console cause I new to qemu
and I want fast                    feedback on stuff like this. I try start
qemu with -D option but the log files never have been              written
by qemu, but either no success.

3) What is the right way to do logging in qemu for development purposes?

Best Regards,

Yali.

Re: [Qemu-devel] Greetings qemu folks

[John Snow]

On 9/7/19 9:58 AM, Toe Dev wrote:
> I am new in QEMU developing and I have general questions about QEMU source
> code as I could not find any guidelines about it.
> 

Hi, welcome!

> 1) I have no success running qemu in nographic mode.
>    The internet says using chardev driver to redirect kernel output to host
> OS...
>    what is the right way to do that?

What have you tried and what were the results?

For me, with standard Fedora installations, I can usually just pass
`-monitor stdio` and get a console in my terminal (along with a GTK window.)

`-nographic` also seems to work just fine.

Post your command line, QEMU version, and the version of the guest OS
you're trying to boot. The guest OS may or may not need to be configured
to actually send output to the console.

> 
> 2) My main target is to output a lot of this to console cause I new to qemu
> and I want fast                    feedback on stuff like this. I try start
> qemu with -D option but the log files never have been              written
> by qemu, but either no success.
> 

QEMU doesn't output a lot of information by default, `-D` might be kind
of misleading. (Actually, I've never used it...)

We have a tracing subsystem, but it might differ from logging in that
you enable tracepoints on a per-trace basis.

Take a look at qemu/docs/devel/tracing.txt for information on driving
the tracing module.

> 3) What is the right way to do logging in qemu for development purposes?
> 

The tracing subsystem.

> Best Regards,
> 
> Yali.
> 

Re: [Qemu-devel] Greetings qemu folks

[Peter Maydell]

On Mon, 9 Sep 2019 at 17:56, John Snow <jsnow@redhat.com> wrote:
> On 9/7/19 9:58 AM, Toe Dev wrote:
> > 2) My main target is to output a lot of this to console cause I new to qemu
> > and I want fast                    feedback on stuff like this. I try start
> > qemu with -D option but the log files never have been              written
> > by qemu, but either no success.
> >
>
> QEMU doesn't output a lot of information by default, `-D` might be kind
> of misleading. (Actually, I've never used it...)

-D just sets the filename for output of -d debug logging. It won't
actually log anything there unless you use the -d option to specify
what to log.

The -d logs are largely useful for doing TCG (emulation) development
work; if KVM is what you care about then tracepoints are probably
more helpful. (Tracepoints work with TCG as well.)

thanks
-- PMM