Re: [Qemu-devel] [RFC PATCH-for-4.2] tracing: Allow to tune tracing options via the environment

[Philippe Mathieu-Daudé]

On 7/3/19 7:25 PM, Daniel P. Berrangé wrote:
> On Wed, Jul 03, 2019 at 07:10:05PM +0200, Philippe Mathieu-Daudé wrote:
>> We can pass trace trace options with the -trace command line
>> argument.
>>
>> Tracing might be useful when running qtests. To avoid to have
>> to modify the tests and recompile, add the possibility to pass
>> trace options via the shell environment.
>>
>> We add:
>> - QEMU_TRACE_EVENTS:    List of events to enable (coma separated)
>> - QEMU_TRACE_EVENTFILE: File with list of events to enable
>> - QEMU_TRACE_LOGFILE:   File to log the trace events.
>>
>> Example of use:
>>
>>   $ QEMU_TRACE_EVENTS=pl011\* make check-qtest-arm
>>     TEST    check-qtest-arm: tests/boot-serial-test
>>   18650@1562168430.027490:pl011_can_receive LCR 0x00000000 read_count 0 
>> returning 1
>>   18650@1562168430.027535:pl011_can_receive LCR 0x00000000 read_count 0 
>> returning 1
>>   18650@1562168430.027544:pl011_can_receive LCR 0x00000000 read_count 0 
>> returning 1
>>   18650@1562168430.028037:pl011_can_receive LCR 0x00000000 read_count 0 
>> returning 1
>>   18650@1562168430.028049:pl011_can_receive LCR 0x00000000 read_count 0 
>> returning 1
>>   18650@1562168430.028057:pl011_can_receive LCR 0x00000000 read_count 0 
>> returning 1
>>   18653@1562168430.053250:pl011_write addr 0x00000000 value 0x00000054
>>   18653@1562168430.053276:pl011_irq_state irq state 0
>>   [...]
>>
>> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
>> ---
>> I'm not sure where to document that...
>> ---
>>  trace/control.c | 9 +++++++++
>>  1 file changed, 9 insertions(+)
>>
>> diff --git a/trace/control.c b/trace/control.c
>> index 43fb7868db..aea802623c 100644
>> --- a/trace/control.c
>> +++ b/trace/control.c
>> @@ -288,6 +288,8 @@ void trace_fini_vcpu(CPUState *vcpu)
>>  
>>  bool trace_init_backends(void)
>>  {
>> +    char *trace_env;
>> +
>>  #ifdef CONFIG_TRACE_SIMPLE
>>      if (!st_init()) {
>>          fprintf(stderr, "failed to initialize simple tracing backend.\n");
>> @@ -306,6 +308,13 @@ bool trace_init_backends(void)
>>      openlog(NULL, LOG_PID, LOG_DAEMON);
>>  #endif
>>  
>> +    trace_init_file(getenv("QEMU_TRACE_LOGFILE"));
>> +    trace_init_events(getenv("QEMU_TRACE_EVENTFILE"));
>> +    trace_env = getenv("QEMU_TRACE_EVENTS");
>> +    if (trace_env) {
>> +        trace_enable_events(trace_env);
>> +    }
>> +
> 
> I don't think it is a nice idea to add this via environment variables
> to QEMU itself. Why not modify libqtest qtest_init_without_qmp_handshake
> to read the env vars and then pass a suitable -trace arg when spawning
> QEMU ?

Fine by me.