Re: [Qemu-devel] [PATCH 2/2] [trivial] Simpler handling of tracetool-generated files in makefiles

[Stefan Hajnoczi]

On Sat, Apr 14, 2012 at 12:19:08AM +0200, Lluís Vilanova wrote:
> Adds 'tracetool-gen' to generate files with tracetool into a temporary file, 
> and
> 'tracetool-ci' to "commit" the generation from the temporaty file into the
> actual destination file if there were any changes in the produced file.
> 
> Signed-off-by: Lluís Vilanova <address@hidden>
> ---
>  Makefile.objs |   19 +++++++++----------
>  rules.mak     |   17 +++++++++++++++++
>  2 files changed, 26 insertions(+), 10 deletions(-)
> 
> diff --git a/Makefile.objs b/Makefile.objs
> index 6d6f24d..b98e905 100644
> --- a/Makefile.objs
> +++ b/Makefile.objs
> @@ -373,18 +373,17 @@ libdis-$(CONFIG_LM32_DIS) += lm32-dis.o
>  # trace
>  
>  ifeq ($(TRACE_BACKEND),dtrace)
> -trace.h: trace.h-timestamp trace-dtrace.h
> -else
> -trace.h: trace.h-timestamp
> +TRACE_H_EXTRA_DEPS=trace-dtrace.h
>  endif
> +trace.h: trace.h-timestamp $(TRACE_H_EXTRA_DEPS)

I like this.

>  trace.h-timestamp: $(SRC_PATH)/trace-events $(BUILD_DIR)/config-host.mak
> -     $(call quiet-command,$(PYTHON) $(SRC_PATH)/scripts/tracetool.py 
> --format=h --backend=$(TRACE_BACKEND) < $< > $@,"  GEN   trace.h")
> -     @cmp -s $@ trace.h || cp $@ trace.h
> +     $(call tracetool-gen,h,$(TRACE_BACKEND))
> +     $(call tracetool-ci)

Here I don't think it's worth introducing an abstraction.  While there
is a pattern I think the abstraction actually hides what is going on
rather than being useful.  The macros are hiding output generation, I
find that especially troubling because you can't really tell what is
going to happen.  It's clearer to leave these statements open coded.

Stefan