Re: [Qemu-devel] [PATCH for-2.8 v1 00/60] Modular build of trace event files

["Lluís Vilanova" <vilanova@ac.upc.edu>]

Daniel P Berrange writes:

> On Tue, Sep 13, 2016 at 08:36:25PM +0200, Lluís Vilanova wrote:
>> Daniel P Berrange writes:
>> 
>> > On Thu, Sep 08, 2016 at 03:23:26PM +0200, Lluís Vilanova wrote:
>> >> Daniel P Berrange writes:
>> >> 
>> >> > I previously split the global trace-events file up into one file
>> >> > per-subdirectory to avoid merge conflict hell.
>> >> [...]
>> >> 
>> >> Sorry, I could not find the message where the infrastructure is modified to
>> >> provide this. But I think there's a more efficient way to provide modular
>> >> auto-generated tracing code without the hierarchical indexing you proposed.
>> 
>> > NB, the simpletrace backend requires a globally unique 32-bit integer ID
>> > to be assigned to each trace event, so even with the approach you suggest
>> > below we still need to be able to assign a global ID for each event.
>> 
>> > So while your suggest below avoids having to pass around the dstate
>> > arrays, which is nice, we still have to assign event id offsets to
>> > each trace-event file in some manner TBD.
>> 
>> Corect me if I'm wrong, but if we only require these consecutive IDs for
>> simpletrace, they don't need to be visible to the tracing headers (these IDs are
>> only used in "trace/generated-tracers.c"). Therefore, we can get them from the
>> trace-events-all file, and minimize the complexity of the changes to tracetool.

> The IDs need to be present in the generated tracers files which are split
> up.

I'm not sure if I'm just missing what you mean.

Changing any of the trace-events files will trigger a recompilation of the .c
files specific to the simpletrace backend, but won't trigger a recompile of all
QEMU files including any of the tracing headers (just the files including the
"trace.h" corresponding to the modified "trace-events").

Cheers,
  Lluis