Re: [PATCH v1] libacpi: use temporary files for generated files

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.10.2020 11:57, Anthony PERARD wrote:
> On Thu, Oct 29, 2020 at 09:47:09AM +0100, Jan Beulich wrote:
>> On 28.10.2020 19:13, Anthony PERARD wrote:
>>> On Tue, Oct 27, 2020 at 12:06:56PM +0100, Jan Beulich wrote:
>>>> On 27.10.2020 11:57, Andrew Cooper wrote:
>>>>> On 27/10/2020 10:37, Jan Beulich wrote:
>>>>>> On 27.10.2020 11:27, Olaf Hering wrote:
>>>>>>> Am Tue, 27 Oct 2020 11:16:04 +0100
>>>>>>> schrieb Jan Beulich <jbeulich@xxxxxxxx>:
>>>>>>>
>>>>>>>> This pattern is used when a rule consists of multiple commands
>>>>>>>> having their output appended to one another's.
>>>>>>> My understanding is: a rule is satisfied as soon as the file exists.
>>>>>> No - once make has found that a rule's commands need running, it'll
>>>>>> run the full set and only check again afterwards.
>>>>>
>>>>> It stops at the first command which fails.
>>>>>
>>>>> Olaf is correct, but the problem here is an incremental build issue, not
>>>>> a parallel build issue.
>>>>>
>>>>> Intermediate files must not use the name of the target, or a failure and
>>>>> re-build will use the (bogus) intermediate state rather than rebuilding 
>>>>> it.
>>>>
>>>> But there's no intermediate file here - the file gets created in one
>>>> go. Furthermore doesn't make delete the target file(s) when a rule
>>>> fails? (One may not want to rely on this, and hence indeed keep multi-
>>>> part rules update intermediate files of different names.)
>>>
>>> What if something went badly enough and sed didn't managed to write the
>>> whole file and make never had a chance to remove the bogus file?
>>
>> How's this different from an object file getting only partly written
>> and not deleted? We'd have to use the temporary file approach in
>> literally every rule if we wanted to cater for this.
> 
> I though that things like `gcc' would write the final object to a
> temporary place then rename it to the final destination, but that
> doesn't seems to be the case.
> 
> I tried to see what happens if the `sed' command fails, and the target is
> created, empty, and doesn't gets deleted by make. So an incremental
> build uses a broken file without trying to rebuild it.

IOW it's rather a courtesy of the compiler / assembler / linker
to delete their output files on error.

> If we want `make' to delete target when a rule fails, I think we need to
> add '.DELETE_ON_ERROR:' somewhere.

Ah, indeed. I thought this was the default nowadays, but the doc
says it isn't. I think this would be preferable over touching
individual rules to go through temporary files.

Jan