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

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Thu, Aug 11, 2016 at 12:11:06PM +0200, Lluís Vilanova wrote:
> 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.

Nevertheless, I agree that @id_offset() should be eliminated to avoid
collisions and manual effort when trace-events files are added.

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