Re: [Qemu-devel] [Qemu-trivial] [PATCH 2/2] Makefile: use full path for qapi-generated directory

[Michael Roth <mdroth@linux.vnet.ibm.com>]

On 12/01/2011 09:19 AM, Stefano Stabellini wrote:
> On Wed, 30 Nov 2011, Stefan Weil wrote:
>> It's common to use either out-of-tree builds or in-tree builds,
>> but not to mix both variants with a common root directory.
>> I think QEMU should explicitly forbid that mixed scenario (like
>> other projects do).
>>
>> Even with your fix there can remain problems with generated
>> header files.
>
> Really? Can you provide more specific details?
>
>> The mixed scenario creates unnecessary complexity.
>> Without the mixed scenario, your patch is not needed.
>
> I agree that supporting the mixed scenario shouldn't be a priority.
> However without this last patch a "make clean" on the main tree is not
> enough to allow out of tree builds.
>
> Try the following scenario:
>
> - cd qemu; ./configure; make
>
> - make clean
>
> - cd ../temp; ./configure --source-path=../qemu; make
>
> this has to work, right? It does not without the patch to fix the
> generation of config-devices.mak.
>

To clarify, the first patch I sent fix a bug that's not currently 
triggered due to qapi-dir always ending up being "qapi-generated/", so 
the guardname generated works, albeit with some needlessly verbose names.

The second isn't intended to fix your issue with builds, but avoid 
potential problems that may arise if at some point $(BUILD_DIR) != 
$(CURDIR).

So they don't actually fix anything, just potential bugs that may arise 
in the future.

The issue with doing out of tree builds with a dirty source directory is 
really just an unsupported scenario. To really clean things up, you need 
to run `make distclean` using the same configuration you used to dirty 
the directory in the first place, otherwise even `make distclean` will 
leave cruft laying in target directories not present in your current config.

Alexandre Raymond sent a patch to make it so that `make distclean` 
always left the source directory pristine, but there was some contention 
on what exactly a `make distclean` entails and it wasn't applied:

http://lists.gnu.org/archive/html/qemu-trivial/2011-07/msg00037.html

That's really the only complete fix for these build issues. I'm starting 
to think it'd be worth it to add a `make clean_for_reals` target that 
does what Alexandre's patch does and tell people to run it after a pull 
or switching to out-of-tree builds.