Re: [libvirt] [PATCH v3 1/3] libxl: implement NUMA capabilities reporting

On mar, 2013-07-16 at 10:41 +0100, Daniel P. Berrange wrote: > On Sat, Jul 13, 2013 at 02:27:03AM +0200, Dario Faggioli wrote: > > @@ -788,9 +903,40 @@ libxlMakeCapabilities(libxl_ctx *ctx) > > return NULL; > > } > > > > - return libxlMakeCapabilitiesInternal(virArchFromHost(), > > + caps = libxlMakeCapabilitiesInternal(virArchFromHost(), > > &phy_info, > > ver_info->capabilities); > > + > > + /* Check if caps is valid. If it is, it must remain so till the end! */ > > + if (caps == NULL) > > + goto out; > > + > > + /* Let's try to fetch NUMA info now (not critical in case we fail) */ > > + numa_info = libxl_get_numainfo(ctx, &nr_nodes); > > + if (numa_info == NULL) > > + VIR_WARN("libxl_get_numainfo failed to retrieve NUMA data"); > > Under what scenario can libxl_get_numainfo() return NULL ? Unless this > is an valid expected scenario, we should treat this is an error. > There are indeed a couple of possible reasons. Actually, I saw that the qemu driver does pretty much the same, i.e., if retrieving NUMA information fails, it gives up on that, but does not make things explode, and I really think it is something that makes sense.

The actual possible failure reasons are: (1) it cannot prepare the parameters for the hypercall, or (2) the hypercall fails. It is true that, in both cases, something really serious might have happened, but there is no way to tell it from here. Thus, I honestly think that trying to carry on is sound... If it is really the case that some critical component died, we'll find out soon enough.