Re: [Xen-devel] [PATCH 2/2] configure: use pkg-config for obtaining xen version

[Juergen Gross <jgross@xxxxxxxx>]

On 24/03/17 16:12, Paul Durrant wrote:
>> -----Original Message-----
>> From: Stefano Stabellini [mailto:sstabellini@xxxxxxxxxx]
>> Sent: 22 March 2017 18:22
>> To: Juergen Gross <jgross@xxxxxxxx>
>> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>; qemu-devel@xxxxxxxxxx;
>> xen-devel@xxxxxxxxxxxxxxxxxxxx; Anthony Perard
>> <anthony.perard@xxxxxxxxxx>; kraxel@xxxxxxxxxx; Paul Durrant
>> <Paul.Durrant@xxxxxxxxxx>
>> Subject: Re: [PATCH 2/2] configure: use pkg-config for obtaining xen version
>>
>> On Wed, 22 Mar 2017, Juergen Gross wrote:
>>> On 21/03/17 19:54, Stefano Stabellini wrote:
>>>> On Tue, 21 Mar 2017, Juergen Gross wrote:
>>>>> On 17/03/17 19:33, Stefano Stabellini wrote:
>>>>>> On Fri, 17 Mar 2017, Juergen Gross wrote:
>>>>>>> On 16/03/17 21:20, Stefano Stabellini wrote:
>>>>>>>> On Thu, 16 Mar 2017, Juergen Gross wrote:
>>>>>>>>> Instead of trying to guess the Xen version to use by compiling
>> various
>>>>>>>>> test programs first just ask the system via pkg-config. Only if it
>>>>>>>>> can't return the version fall back to the test program scheme.
>>>>>>>>
>>>>>>>> That's OK, but why did you remove the Xen unstable test?
>>>>>>>
>>>>>>> >From Xen 4.9 on pkg-config will return the needed information.
>> There is
>>>>>>> no longer a need for a test program to determine the Xen version.
>> After
>>>>>>> all this was the main objective of my series adding the pkg-config
>>>>>>> files to Xen.
>>>>>>
>>>>>> I was going to say something like "yeah, but is pkg-config always
>>>>>> available?" In reality, QEMU already has pkg-config as build
>>>>>> dependency, so I guess there is no problem with that.
>>>>>>
>>>>>> Please add a note about this to the commit message.
>>>>>>
>>>>>
>>>>> Okay.
>>>>
>>>> Sorry to point this out only now, and I realize that it might be
>>>> unimportant for production builds, but it is important to me, and
>>>> developers in general, to be able to test a single QEMU tree against a
>>>> number of Xen trees (all releases from 4.3 onward).
>>>>
>>>> With this change (specifically dropping the 4.9 build test), out of tree
>>>> builds don't work anymore. I would like to be able to do:
>>>>
>>>> ./configure --enable-xen --target-list=i386-softmmu \
>>>>                 --extra-cflags="-I$DIR/tools/include \
>>>>                 -I$DIR/tools/libs/toollog/include \
>>>>                 -I$DIR/tools/libs/evtchn/include \
>>>>                 -I$DIR/tools/libs/gnttab/include \
>>>>                 -I$DIR/tools/libs/foreignmemory/include \
>>>>                 -I$DIR/tools/libs/devicemodel/include \
>>>>                 -I$DIR/tools/libxc/include \
>>>>                 -I$DIR/tools/xenstore/include \
>>>>                 -I$DIR/tools/xenstore/compat/include" \
>>>>                 --extra-ldflags="-L$DIR/tools/libxc \
>>>>                 -L$DIR/tools/xenstore \
>>>>                 -L$DIR/tools/libs/evtchn \
>>>>                 -L$DIR/tools/libs/gnttab \
>>>>                 -L$DIR/tools/libs/foreignmemory \
>>>>                 -L$DIR/tools/libs/devicemodel \
>>>>                 -Wl,-rpath-link=$DIR/tools/libs/toollog \
>>>>                 -Wl,-rpath-link=$DIR/tools/libs/evtchn \
>>>>                 -Wl,-rpath-link=$DIR/tools/libs/gnttab \
>>>>                 -Wl,-rpath-link=$DIR/tools/libs/call \
>>>>                 -Wl,-rpath-link=$DIR/tools/libs/foreignmemory \
>>>>                 -Wl,-rpath-link=$DIR/tools/libs/devicemodel" \
>>>>             --disable-kvm
>>>> make
>>>>
>>>> And the make should succeed. Is there a way to do that with pkg-config?
>>>
>>> Sure, for Xen 4.9 just do:
>>>
>>> PKG_CONFIG_PATH=$(DIR)/tools/pkg-config ./configure \
>>>             --enable-xen --target-list=i386-softmmu \
>>>             --disable-kvm
>>> make
>>
>> Yes, that works, thanks! I committed it to my next branch adding
>> "pkg-config, which is already a build dependency of QEMU, will be used
>> exclusively to determine the Xen version from Xen 4.9 onward." to the
>> commit message.
> 
> A further question...
> 
> I have a xen tree which I've been using to build and install master against 
> my own checked out QEMU repo. No problem with that. I've now reverted my tree 
> to 4.7.0 and cannot build tools (even after a make distclean) because QEMU's 
> configure is still getting up a xen_ctrl_version of 40900. This is because 
> pkg-config is still finding a 4.9.0 xencontrol package? Where is it getting 
> this from?

Hmm, could it be you have Xen unstable installed on your machine?

Didn't think of this problem. I can think of 3 solutions:

a) delete the xencontrol.pc file (on my system under
   /usr/share/pkgconfig/ )

b) we add a patch to qemu to test an environment variable whether
   pkg-config should be ignored for Xen version detection

c) set the environment variable PKG_CONFIG_LIBDIR to a local directory
   and copy all but the xen*.pc files from /usr/share/pkgconfig/ (or
   your correct directory) to it (or link them to avoid missing updates)

OTOH this is something you have to be aware of for other packages as
well: mixing the build environment and the target environment can lead
to bad results. Now Xen has been added to the list.


Juergen


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