Re: [Xen-devel] Fixing libvirt's libxl driver breakage -- where to define LIBXL_API_VERSION?

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On Tue, Apr 12, 2016 at 10:31 PM, Jim Fehlig <jfehlig@xxxxxxxx> wrote:
> Wei Liu wrote:
>> Hi libvirt maintainers,
>
> Sorry for the delay. Slowly catching up on mail after vacation...
>
>>
>> Xen's control library libxenlight (libxl) requires application
>> (libvirt in this case) to explictily define LIBXL_API_VERSION.
>
> Where is this requirement written? :-)
>
>> This is
>> lacking at the moment so libvirt's libxl driver always gets the latest
>> APIs.
>
> IMO, that is what we want for upstream libvirt. Downstreams can choose a
> specific version if they want.

I think one of us isn't understanding the situation properly. Is it
not the case that currently, all releases of libvirt *will not
compile* against Xen 4.7 once it's released?  So people downloading
and building libvirt will have to either 1) root around and try to
figure out what version of Xen it will build against, 2) manually add
in a #define *with the correct API version* to a header somewhere to
make it build properly, or 3) update to a version of libvirt that
supports the new api (which at the moment hasn't even been released
yet)?

All of those options are completely unacceptable.  Older versions of
libvirt should Just Work when compiled against newer versions of Xen.

I think it does make sense to have the libvirt development branch not
specify an API version; but when it branches for release, it should
set LIBXL_API_VERSION to whatever the current version is at the time
of the branch.

 -George

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