Re: [PATCH] tools/libs/light: fix race in Makefile

[Jürgen Groß <jgross@xxxxxxxx>]

On 26.10.20 10:34, Jan Beulich wrote:
> On 25.10.2020 11:12, Juergen Gross wrote:
> > The header $(INCLUDE)/_lixl_list.h matches two different rules, which
> > can result in build breakage. Fix that.
> While I don't doubt you having observed a race, I'm not sure this is
> true, and hence I'm also not sure the change is going to address it:
> Aiui the two rules you talk about are the one you change and
>
> $(XEN_INCLUDE)/_%.h: _%.h
>         $(call move-if-changed,_$*.h,$(XEN_INCLUDE)/_$*.h)
>
> But a pattern rule doesn't come into play when a specific rule for
> a file exists.
Hmm, true. I didn't see the race, but spotted the suspected ambiguity
just by chance.

> What I don't understand here is why this two step moving around of
> headers is used: Instead of the above pattern rule, can't the rule
> to generate _libxl_type%.h, _libxl_type%_json.h,
> _libxl_type%_private.h, and _libxl_type%.c put the relevant header
> files right into their designated place? This would allow the
> pattern rule to go away, albeit I'd then still be unclear about
> the specific race you did observe.
This would require to replace the pattern rules used to generate the
files by per-file rules instead, as e.g. _libxl_types_json.h and
_libxl_types_internal_json.h are matching the same pattern, but they
need to end up in different directories.

In the end I think this patch can just be dropped.

Sorry for the noise,

Juergen