Re: [Xen-devel] [PATCH] libxl: use LIBXL_API_VERSION 0x040200

[Jim Fehlig <jfehlig@xxxxxxxx>]

George Dunlap wrote:
> On Thu, Apr 14, 2016 at 12:37 AM, Jim Fehlig <jfehlig@xxxxxxxx> wrote:
>> To ensure the libvirt libxl driver will build with future versions
>> of Xen where the libxl API may change in incompatible ways,
>> explicitly use LIBXL_API_VERSION 0x040200. The libxl driver
>> does use new libxl APIs that have been added since Xen 4.2, but
>> currently it does not make use of any changes made to existing
>> APIs such as libxl_domain_create_restore or libxl_set_vcpuaffinity.
>> The version can be bumped if/when the libxl driver consumes the
>> changed APIs.
>>
>> Further details can be found in the following discussion thread
>>
>> https://www.redhat.com/archives/libvir-list/2016-April/msg00178.html
>> Signed-off-by: Jim Fehlig <jfehlig@xxxxxxxx>
>> ---
>>  src/Makefile.am          |  1 +
>>  src/libxl/libxl_conf.h   | 12 ------------
>>  src/libxl/libxl_domain.c | 15 ---------------
>>  3 files changed, 1 insertion(+), 27 deletions(-)
>>
>> diff --git a/src/Makefile.am b/src/Makefile.am
>> index 08ff301..259a474 100644
>> --- a/src/Makefile.am
>> +++ b/src/Makefile.am
>> @@ -1311,6 +1311,7 @@ endif ! WITH_DRIVER_MODULES
>>
>>  libvirt_driver_libxl_impl_la_CFLAGS =          \
>>                 $(LIBXL_CFLAGS)                 \
>> +               -DLIBXL_API_VERSION=0x040200    \
>>                 -I$(srcdir)/access      \
>>                 -I$(srcdir)/conf        \
>>                 -I$(srcdir)/secret      \
>> diff --git a/src/libxl/libxl_conf.h b/src/libxl/libxl_conf.h
>> index 3c0eafb..24e2911 100644
>> --- a/src/libxl/libxl_conf.h
>> +++ b/src/libxl/libxl_conf.h
>> @@ -69,18 +69,6 @@
>>  # endif
>>
>>
>> -/* libxl interface for setting VCPU affinity changed in 4.5. In fact, a new
>> - * parameter has been added, representative of 'VCPU soft affinity'. If one
>> - * does not care about it (and that's libvirt case), passing NULL is the
>> - * right thing to do. To mark that change, LIBXL_HAVE_VCPUINFO_SOFT_AFFINITY
>> - * is defined. */
>> -# ifdef LIBXL_HAVE_VCPUINFO_SOFT_AFFINITY
>> -#  define libxl_set_vcpuaffinity(ctx, domid, vcpuid, map) \
>> -    libxl_set_vcpuaffinity((ctx), (domid), (vcpuid), (map), NULL)
>> -#  define libxl_set_vcpuaffinity_all(ctx, domid, max_vcpus, map) \
>> -    libxl_set_vcpuaffinity_all((ctx), (domid), (max_vcpus), (map), NULL)
>> -# endif
> 
> Just checking with this -- the LIBXL_API_VERSION is meant for
> *forward* compatibility, but I think the LIBXL_HAVE_* macros are for
> *backwards* compatibility, isn't that right?  If you compile this
> against an older version of Xen without LIBXL_HAVE_VCPU_SOFT_AFFINITY
> (say, 4.4), will it break with this patch?

I've tested the patch (well, actually a variant that moves
'-DLIBXL_API_VERSION=0x040200' to configure.ac as suggested by Martin) by
building against 4.2, 4.3, 4.4, and 4.7/master. I think Dario already did a good
job explaining the removal of the above hunk.

Regards,
Jim

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