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 12:42 PM, Stefano Stabellini wrote:
> On Thu, 1 Dec 2011, Anthony Liguori wrote:
>> On 12/01/2011 12:11 PM, Stefan Weil wrote:
>>> Am 01.12.2011 16:19, schrieb Stefano Stabellini:
>>>> 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?
>>>
>>> Yes. Suppose different generated header files with the same name
>>> exist in the source directory tree and in the build directory tree.
>>>
>>> Then compiler options (the order of -I options) will determine
>>> which of two header files with same name will be used in out-of-tree
>>> builds. If the wrong one (that from the source directory tree) is used,
>>> the compiler might fail or produce wrong code (for example when
>>> macro values changed).
>>>>> 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
>>>
>>> Which ./configure do you run in an empty temp directory?
>>> This example (like similar ones in your previous mail) won't work.
>>
>> Yes, you must do external builds only from a clean source directory.  This is a
>> perfectly normal requirement.  In fact, I can't think of a project that doesn't
>> require this.
>
> Fair enough.
>
> In that case, like Michael Roth wrote, the patch "Makefile: use full
> path for qapi-generated directory" doesn't actually fix anything, so
> probably we don't need it either, but I'll leave it up to you.
>

Yup, it's just to address some potential issues/suggestions Stefan Weil 
pointed out. I think patch 1 should be applied though.