On lun, 2014-06-30 at 08:11 +0100, Ian Campbell wrote: > On Sun, 2014-06-29 at 18:35 +0100, xen.org wrote: > >> branch xen-unstable >> xen branch xen-unstable >> job build-i386-libvirt >> test libvirt-build >> >> Tree: gnulib_libvirt git://drall.uk.xensource.com:9419/git://git.sv.gnu.org/gnulib.git%20[fetc... >> Tree: libvirt git://xenbits.xen.org/libvirt.git >> Tree: qemu git://xenbits.xen.org/staging/qemu-xen-unstable.git >> Tree: qemuu git://xenbits.xen.org/staging/qemu-upstream-unstable.git >> Tree: xen git://xenbits.xen.org/xen.git >> >> *** Found and reproduced problem changeset *** >> >> Bug is in tree: xen git://xenbits.xen.org/xen.git >> Bug introduced: 871b43a309d80ac99458c13c2c3da8d15c482d30 >> Bug not present: 6cc89d3101d8874e01a69a89a65736a2adfbd199 >> >> >> commit 871b43a309d80ac99458c13c2c3da8d15c482d30 >> Author: Dario Faggioli <dario.faggioli(a)citrix.com&gt; >> Date: Fri Jun 20 18:19:12 2014 +0200 >> >> libxl: get and set soft affinity >> > Dario, > > libvirt doesn't use the LIBXL_API_VERSION mechanism but instead uses the > LIBXL_HAVE stuff to retain compatibility. > > Will you be able to send a patch against libvirt today to make it use > the new interface (conditional on LIBXL_HAVE_VCPUINFO_SOFT_AFFINITY)? > > So, brief recap for the ones not knowing the details of this, libxl interface for vcpu pinning is changing (basically, libxl_set_vcpuaffinity() wants one more param). Libxl provides some ifdefs for these situations, and in this case, the gate to be used is, as Ian is saying: #ifdef LIBXL_HAVE_VCPUINFO_SOFT_AFFINITY One possible approach is to enclose all the calls into such #ifdef-#endif but, although there are only two of them right now, I don't like it (what if we need more calls in the future?). I could come up with the alternatives attached to this message. In patch1, I use the new interface in the code and #define it to the old one if !LIBXL_HAV_VCPUINFO_SOFT_AFFINITY. In patch2 I do the opposite (keep old interface in the code and redefine to new, with additional param equal to NULL).

I like patch1 better, but I think it can cause "unused variable" like warnings if, at some point in future, we will actually use the new soft affinity parameter, when compiling on a version of libxl that does not define HAVE_VCPUINFO_SOFT_AFFINITY, can't it?

If yes, is it an issue?

If yes, a big enough one to make us prefer patch2?