Re: [PATCH] libxl: avoid golang building without CONFIG_GOLANG=y

[Nick Rosbrook <rosbrookn@xxxxxxxxx>]

On Tue, Aug 4, 2020 at 12:02 PM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>
> On 04.08.2020 17:57, Wei Liu wrote:
> > On Tue, Aug 04, 2020 at 05:53:49PM +0200, Jan Beulich wrote:
> >> On 04.08.2020 17:50, Wei Liu wrote:
> >>> On Tue, Aug 04, 2020 at 05:30:40PM +0200, Jan Beulich wrote:
> >>>> On 04.08.2020 17:22, Nick Rosbrook wrote:
> >>>>> On Tue, Aug 4, 2020 at 10:17 AM Wei Liu <wl@xxxxxxx> wrote:
> >>>>>>
> >>>>>> On Mon, Aug 03, 2020 at 10:06:32AM +0200, Jan Beulich wrote:
> >>>>>>> While this doesn't address the real problem I've run into (attempting 
> >>>>>>> to
> >>>>>>> update r/o source files), not recursing into tools/golang/xenlight/ is
> >>>>>>> enough to fix the build for me for the moment. I don't currently see 
> >>>>>>> why
> >>>>>>> 60db5da62ac0 ("libxl: Generate golang bindings in libxl Makefile") 
> >>>>>>> found
> >>>>>>> it necessary to invoke this build step unconditionally.
> >>>>>>>
> >>>>>>
> >>>>>> Perhaps an oversight?
> >>>>>
> >>>>> This is intentional, and I think the commit message in 60db5da62ac0
> >>>>> ("libxl: Generate golang bindings in libxl Makefile") explains the
> >>>>> reasoning well. But, to summarize, CONFIG_GOLANG is only used to
> >>>>> control the bindings actually being compiled (i.e. with `go build`).
> >>>>> However, we always want the code generation script
> >>>>> (tools/golang/xenlight/gengotypes.py) to run if e.g.
> >>>>> tools/libxl/libxl_types.idl is modified.
> >>>>>
> >>>>> I hope this helps.
> >>>>
> >>>> Not really - I'm still not seeing the "why" behind this behavior. I.e.
> >>>> why build _anything_ that's not used further in the build, nor getting
> >>>> installed? Also if (aiui) you effectively object to the change that
> >>>> Wei has given his ack for, would you mind providing an alternative fix
> >>>> for the problem at hand?
> >>>
> >>> Is the solution here to make the target check if IDL definition file is
> >>> actually changed before regenerating the bindings?
> >>
> >> I don't know - Nick? A move-if-changed based approach would likely deal
> >> with the r/o source problem at the same time (at least until such time
> >> where the directory containing the file(s) is also r/o).
> >
> > To make sure Nick and I understand your use case correct -- "r/o source
> > problem" means you want the tools source to be read-only? But you would
> > be fine recursing into tools directory to build all the libraries and
> > programs?
>
> Yes - until we support out-of-tree builds, nothing more can be expected
> to work.
>

Jan - is the problem specifically that a fresh clone,  or `git
checkout`, etc. changes file timestamps in a way that triggers make to
rebuild those targets? I have not used the move-if-changed approach
before, but AFAICT that would be sufficient.

-NR