Re: [Qemu-devel] [PATCH for-2.8 v1 60/60] trace: update docs to reflect new code generation approach

[Lluís Vilanova]

Daniel P Berrange writes:

> On Wed, Aug 10, 2016 at 06:11:24PM +0200, Lluís Vilanova wrote:
>> Daniel P Berrange writes:
>> 
>> > On Wed, Aug 10, 2016 at 04:33:47PM +0200, Lluís Vilanova wrote:
>> >> Daniel P Berrange writes:
[...]
>> >> For example, first we concatenate /trace-events, /io/trace-events and
>> >> /hw/usb/trace-events into /trace-events-all to produce:
>> >> 
>> >> @group core
>> >> @dir /
>> >> # contents of /trace-events
>> >> @group io
>> >> @dir /io
>> >> # contents of /io/trace-events
>> >> @group hw_usb
>> >> @dir /hw/usb
>> >> # contents of /hw/usb/trace-events
>> >> 
>> >> Then we can use /trace-events-all to generate all the per-directory 
>> >> trace.h
>> >> files while ensuring a perfectly flat event identifier space (a single
>> >> generated-events.c is used).
>> >> 
>> >> This should minimize changes to tracing code and avoid further 
>> >> restrictions
>> >> (like the "top-level vcpu" one).
>> 
>> > That means when any individual trace file is changed, we re-generate the
>> > world, which is exactly what this series is designed to avoid.
>> 
>> Nope. We re-generate /trace-events-all, but each individual file generated
>> afterwards (taken from the "@dir" directive) will change only if its new
>> contents do (the Makefile uses cmp to check if files need updating from their
>> corresponding timestamp file).

> The contents will still need to change too if we have a global numbering
> space as your suggestion requires. The event groups are the only way to
> avoid that.

Aha, that's true. I didn't think of that, sorry.


Cheers,
  Lluis