conf: support reporting maxCount attribute for virtual_functions cap

Report the maximum possible number of VFs for an SRIOV PF, like this:

   <capability type='virtual_functions' maxCount='7'>
      ...
   </capability>

I've just discovered that the virtual_functions and physical_functions
capabilities are not supported in the virNodeDeviceParse functions,
only in virNodeDeviceFormat (I suppose because they are only reported,
not set from XML). This should probably be remedied, but is less
immediately useful than the current patch.

docs/formatnode.html.in

@@ -108,7 +108,16 @@
                 the type is <code>virtual_functions</code>, then this
                 device is an SRIOV PF, and the capability element will
                 have a list of <code>address</code> subelements, one
-                for each VF on this PF.
+                for each VF on this PF. If the host system supports
+                reporting it (via the "sriov_maxvfs" file in the
+                device's sysfs directory) the capability element will
+                also have an attribute named <code>maxCount</code>
+                which is the maximum number of SRIOV VFs supported by
+                this device, which could be higher than the number of
+                VFs that are curently active <span class="since">since
+                1.3.0</span>; in this case, even if there are
+                currently no active VFs the virtual_functions
+                capabililty will still be shown.
               </dd>
               <dt><code>numa</code></dt>
               <dd>

src/conf/node_device_conf.c

@@ -361,19 +361,27 @@ char *virNodeDeviceDefFormat(const virNodeDeviceDef *def)
                 virBufferAddLit(&buf, "</capability>\n");
             }
             if (data->pci_dev.flags & VIR_NODE_DEV_CAP_FLAG_PCI_VIRTUAL_FUNCTION) {
-                virBufferAddLit(&buf, "<capability type='virt_functions'>\n");
-                virBufferAdjustIndent(&buf, 2);
-                for (i = 0; i < data->pci_dev.num_virtual_functions; i++) {
-                    virBufferAsprintf(&buf,
-                                      "<address domain='0x%.4x' bus='0x%.2x' "
-                                      "slot='0x%.2x' function='0x%.1x'/>\n",
-                                      data->pci_dev.virtual_functions[i]->domain,
-                                      data->pci_dev.virtual_functions[i]->bus,
-                                      data->pci_dev.virtual_functions[i]->slot,
-                                      data->pci_dev.virtual_functions[i]->function);
+                virBufferAddLit(&buf, "<capability type='virt_functions'");
+                if (data->pci_dev.max_virtual_functions)
+                    virBufferAsprintf(&buf, " maxCount='%u'",
+                                      data->pci_dev.max_virtual_functions);
+                if (data->pci_dev.num_virtual_functions == 0) {
+                    virBufferAddLit(&buf, "/>\n");
+                } else {
+                    virBufferAddLit(&buf, ">\n");
+                    virBufferAdjustIndent(&buf, 2);
+                    for (i = 0; i < data->pci_dev.num_virtual_functions; i++) {
+                        virBufferAsprintf(&buf,
+                                          "<address domain='0x%.4x' bus='0x%.2x' "
+                                          "slot='0x%.2x' function='0x%.1x'/>\n",
+                                          data->pci_dev.virtual_functions[i]->domain,
+                                          data->pci_dev.virtual_functions[i]->bus,
+                                          data->pci_dev.virtual_functions[i]->slot,
+                                          data->pci_dev.virtual_functions[i]->function);
+                    }
+                    virBufferAdjustIndent(&buf, -2);
+                    virBufferAddLit(&buf, "</capability>\n");
                 }
-                virBufferAdjustIndent(&buf, -2);
-                virBufferAddLit(&buf, "</capability>\n");
             }
             if (data->pci_dev.nIommuGroupDevices) {
                 virBufferAsprintf(&buf, "<iommuGroup number='%d'>\n",

src/conf/node_device_conf.h

@@ -112,6 +112,7 @@ typedef struct _virNodeDevCapData {
             virPCIDeviceAddressPtr physical_function;
             virPCIDeviceAddressPtr *virtual_functions;
             size_t num_virtual_functions;
+            unsigned int max_virtual_functions;
             unsigned int flags;
             virPCIDeviceAddressPtr *iommuGroupDevices;
             size_t nIommuGroupDevices;