Re: [Qemu-devel] Patch to add helpful tracing output for driver authors in NVMe emulation

["Daniel P. Berrange" <berrange@redhat.com>]

On Fri, Oct 06, 2017 at 09:58:33AM -0400, Doug Gale wrote:
> I tried to get tracing to work before and I have never gotten it
> working. I'll give it another try and redo the patch with tracing
> infrastructure if necessary. The printf are nice because the dev can
> just look at the terminal where qemu is running. Can you view the
> trace output in realtime? When their code is sitting at a breakpoint
> in their driver, can they see the last thing that was traced right
> there? Or do they have to go run some cumbersome command and wade
> through it after an entire test run after the vm shut down?

There's a variety of trace backends available. By default QEMU enables
the 'log' backend these days. So with a default build of QEMU you can
use the '-d' arg to turn on printing: eg.:

   qemu-system-x86_64 ...args...    -d trace:qio*

and that'll turn on every tracepoint with 'qio' as a prefix. The
trace messages will be printed straight to the console. eg:

$ qemu-system-x86_64 -d trace:qio* -serial unix:/tmp/foo,server
15774@1507298448.842745:qio_channel_socket_new Socket new ioc=0x5598b0565d60
15774@1507298448.842757:qio_channel_socket_listen_sync Socket listen sync ioc=0x5598b0565d60 addr=0x5598b0565c50
15774@1507298448.842803:qio_channel_socket_listen_complete Socket listen complete ioc=0x5598b0565d60 fd=16
qemu-system-x86_64: -serial unix:/tmp/foo,server: info: QEMU waiting for connection on: disconnected:unix:/tmp/foo,server
15774@1507298448.842818:qio_channel_socket_new Socket new ioc=0x5598b0564060
15774@1507298448.842820:qio_channel_socket_accept Socket accept start ioc=0x5598b0565d60


Regards,
Daniel
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