qemu: do upfront check for vcpupids being null when querying pinning

The qemuDomainHelperGetVcpus attempted to report an error when the
vcpupids info was NULL. Unfortunately earlier code would clamp the
value of 'maxinfo' to 0 when nvcpupids was 0, so the error reporting
would end up being skipped.

This lead to 'virsh vcpuinfo <dom>' just returning an empty list
instead of giving the user a clear error.

(cherry picked from commit 9358b63a)

src/qemu/qemu_driver.c

@@ -1380,6 +1380,12 @@ qemuDomainHelperGetVcpus(virDomainObjPtr vm, virVcpuInfoPtr info, int maxinfo,
     if ((hostcpus = nodeGetCPUCount()) < 0)
         return -1;
 
+    if (priv->vcpupids == NULL) {
+        virReportError(VIR_ERR_OPERATION_INVALID,
+                       "%s", _("cpu affinity is not supported"));
+        return -1;
+    }
+
     maxcpu = maplen * 8;
     if (maxcpu > hostcpus)
         maxcpu = hostcpus;
@@ -1395,8 +1401,7 @@ qemuDomainHelperGetVcpus(virDomainObjPtr vm, virVcpuInfoPtr info, int maxinfo,
                 info[i].number = i;
                 info[i].state = VIR_VCPU_RUNNING;
 
-                if (priv->vcpupids != NULL &&
-                    qemuGetProcessInfo(&(info[i].cpuTime),
+                if (qemuGetProcessInfo(&(info[i].cpuTime),
                                        &(info[i].cpu),
                                        NULL,
                                        vm->pid,
@@ -1410,28 +1415,22 @@ qemuDomainHelperGetVcpus(virDomainObjPtr vm, virVcpuInfoPtr info, int maxinfo,
 
         if (cpumaps != NULL) {
             memset(cpumaps, 0, maplen * maxinfo);
-            if (priv->vcpupids != NULL) {
-                for (v = 0; v < maxinfo; v++) {
-                    unsigned char *cpumap = VIR_GET_CPUMAP(cpumaps, maplen, v);
-                    virBitmapPtr map = NULL;
-                    unsigned char *tmpmap = NULL;
-                    int tmpmapLen = 0;
-
-                    if (virProcessGetAffinity(priv->vcpupids[v],
-                                              &map, maxcpu) < 0)
-                        return -1;
-                    virBitmapToData(map, &tmpmap, &tmpmapLen);
-                    if (tmpmapLen > maplen)
-                        tmpmapLen = maplen;
-                    memcpy(cpumap, tmpmap, tmpmapLen);
-
-                    VIR_FREE(tmpmap);
-                    virBitmapFree(map);
-                }
-            } else {
-                virReportError(VIR_ERR_OPERATION_INVALID,
-                               "%s", _("cpu affinity is not available"));
-                return -1;
+            for (v = 0; v < maxinfo; v++) {
+                unsigned char *cpumap = VIR_GET_CPUMAP(cpumaps, maplen, v);
+                virBitmapPtr map = NULL;
+                unsigned char *tmpmap = NULL;
+                int tmpmapLen = 0;
+
+                if (virProcessGetAffinity(priv->vcpupids[v],
+                                          &map, maxcpu) < 0)
+                    return -1;
+                virBitmapToData(map, &tmpmap, &tmpmapLen);
+                if (tmpmapLen > maplen)
+                    tmpmapLen = maplen;
+                memcpy(cpumap, tmpmap, tmpmapLen);
+
+                VIR_FREE(tmpmap);
+                virBitmapFree(map);
             }
         }
     }