Stefan Hajnoczi writes:
> On Fri, Aug 05, 2016 at 06:59:34PM +0200, Lluís Vilanova wrote:
>> +# hypertrace
>> +hyperargs=$hypertrace
>> +if test $hypertrace = "disabled"; then
>> +hyperargs=0
>> +fi
>> +echo "CONFIG_HYPERTRACE_ARGS=$hyperargs" >> $config_host_mak
>> +hypertrace_events=hypertrace/trace-events
>> +mkdir -p $(dirname $hypertrace_events)
>> +echo "# See docs/trace-events.txt for syntax documentation."
>> >$hypertrace_events
>> +echo -n 'vcpu guest_hypertrace(' >>$hypertrace_events
>> +for i in `seq $hypertrace`; do
>> +if test $i != 1; then
>> +echo -n ", " >>$hypertrace_events
>> +fi
>> +echo -n "uint64_t arg$i" >>$hypertrace_events
>> +done
>> +echo -n ') ' >>$hypertrace_events
>> +for i in `seq $hypertrace`; do
>> +echo -n "\" arg$i=0x%016\"PRIx64" >>$hypertrace_events
>> +done
>> +echo >>$hypertrace_events
> This reminds me of the first versions of "simpletrace" where the number
> of arguments was fixed and argument size was fixed.
> This meant strings cannot be traced, number of arguments is limited, and
> you pay an space overhead for unused arguments.
> Later on the format was changed to header (including .length field) and
> binary data payload. This reduced the space overhead, elminated the
> argument count limit, and allowed strings to be traced.
> I think these are desirable qualities for any tracing mechanism and
> would reconsider a fixed number of uint64_t arguments.
The number of arguments is fixed at *compilation time*. What is not supported
out of the box is multiplexing multiple guest events over the hypertrace
event. That is, you need to do it yourself when post-processing the traces, but
I don't think that's too bad.
Cheers,
Lluis
