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

From: Jan Beulich <jbeulich@suse.com>
To: Nick Rosbrook <rosbrookn@gmail.com>
Cc: Anthony Perard <anthony.perard@citrix.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	George Dunlap <george.dunlap@citrix.com>, Wei Liu <wl@xen.org>
Subject: Re: [PATCH] libxl: avoid golang building without CONFIG_GOLANG=y
Date: Wed, 5 Aug 2020 08:35:04 +0200	[thread overview]
Message-ID: <6e83d698-64bb-68f0-b046-b20bf6db1c56@suse.com> (raw)
In-Reply-To: <CAEBZRSc=xUjYq7ao9Rv-EEJsjiBkt5mio5QofvixErZj_SJUcw@mail.gmail.com>

On 04.08.2020 18:41, Nick Rosbrook wrote:
> On Tue, Aug 4, 2020 at 12:02 PM Jan Beulich <jbeulich@suse.com> 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@xen.org> 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?

Afaict it's not deterministic in which order files get created / updated,
and hence the generated files may or may not appear older than their
dependencies.

Jan