qemu: cgroup: Extract temporary relaxing of cgroup setting for vcpu hotplug

When hot-adding vcpus qemu needs to allocate some structures in the DMA
zone which may be outside of the numa pinning. Extract the code doing
this in a set of helpers so that it can be reused.

src/qemu/qemu_cgroup.c

@@ -1127,3 +1127,93 @@ qemuRemoveCgroup(virDomainObjPtr vm)
 
     return virCgroupRemove(priv->cgroup);
 }
+
+
+static void
+qemuCgroupEmulatorAllNodesDataFree(qemuCgroupEmulatorAllNodesDataPtr data)
+{
+    if (!data)
+        return;
+
+    virCgroupFree(&data->emulatorCgroup);
+    VIR_FREE(data->emulatorMemMask);
+    VIR_FREE(data);
+}
+
+
+/**
+ * qemuCgroupEmulatorAllNodesAllow:
+ * @cgroup: domain cgroup pointer
+ * @retData: filled with structure used to roll back the operation
+ *
+ * Allows all NUMA nodes for the qemu emulator thread temporarily. This is
+ * necessary when hotplugging cpus since it requires memory allocated in the
+ * DMA region. Afterwards the operation can be reverted by
+ * qemuCgrouEmulatorAllNodesRestore.
+ *
+ * Returns 0 on success -1 on error
+ */
+int
+qemuCgroupEmulatorAllNodesAllow(virCgroupPtr cgroup,
+                                qemuCgroupEmulatorAllNodesDataPtr *retData)
+{
+    qemuCgroupEmulatorAllNodesDataPtr data = NULL;
+    char *all_nodes_str = NULL;
+    virBitmapPtr all_nodes = NULL;
+    int ret = -1;
+
+    if (!virNumaIsAvailable() ||
+        !virCgroupHasController(cgroup, VIR_CGROUP_CONTROLLER_CPUSET))
+        return 0;
+
+    if (!(all_nodes = virNumaGetHostNodeset()))
+        goto cleanup;
+
+    if (!(all_nodes_str = virBitmapFormat(all_nodes)))
+        goto cleanup;
+
+    if (VIR_ALLOC(data) < 0)
+        goto cleanup;
+
+    if (virCgroupNewThread(cgroup, VIR_CGROUP_THREAD_EMULATOR, 0,
+                           false, &data->emulatorCgroup) < 0)
+        goto cleanup;
+
+    if (virCgroupGetCpusetMems(data->emulatorCgroup, &data->emulatorMemMask) < 0 ||
+        virCgroupSetCpusetMems(data->emulatorCgroup, all_nodes_str) < 0)
+        goto cleanup;
+
+    VIR_STEAL_PTR(*retData, data);
+    ret = 0;
+
+ cleanup:
+    VIR_FREE(all_nodes_str);
+    virBitmapFree(all_nodes);
+    qemuCgroupEmulatorAllNodesDataFree(data);
+
+    return ret;
+}
+
+
+/**
+ * qemuCgrouEmulatorAllNodesRestore:
+ * @data: data structure created by qemuCgroupEmulatorAllNodesAllow
+ *
+ * Rolls back the setting done by qemuCgroupEmulatorAllNodesAllow and frees the
+ * associated data.
+ */
+void
+qemuCgrouEmulatorAllNodesRestore(qemuCgroupEmulatorAllNodesDataPtr data)
+{
+    virErrorPtr err;
+
+    if (!data)
+        return;
+
+    err = virSaveLastError();
+    virCgroupSetCpusetMems(data->emulatorCgroup, data->emulatorMemMask);
+    virSetError(err);
+    virFreeError(err);
+
+    qemuCgroupEmulatorAllNodesDataFree(data);
+}

src/qemu/qemu_cgroup.h

@@ -57,4 +57,15 @@ int qemuSetupCgroupCpusetCpus(virCgroupPtr cgroup, virBitmapPtr cpumask);
 int qemuSetupGlobalCpuCgroup(virDomainObjPtr vm);
 int qemuRemoveCgroup(virDomainObjPtr vm);
 
+typedef struct _qemuCgroupEmulatorAllNodesData qemuCgroupEmulatorAllNodesData;
+typedef qemuCgroupEmulatorAllNodesData *qemuCgroupEmulatorAllNodesDataPtr;
+struct _qemuCgroupEmulatorAllNodesData {
+    virCgroupPtr emulatorCgroup;
+    char *emulatorMemMask;
+};
+
+int qemuCgroupEmulatorAllNodesAllow(virCgroupPtr cgroup,
+                                    qemuCgroupEmulatorAllNodesDataPtr *data);
+void qemuCgrouEmulatorAllNodesRestore(qemuCgroupEmulatorAllNodesDataPtr data);
+
 #endif /* __QEMU_CGROUP_H__ */

src/qemu/qemu_driver.c

@@ -4853,11 +4853,7 @@ qemuDomainSetVcpusLive(virQEMUDriverPtr driver,
                        unsigned int nvcpus)
 {
     qemuDomainObjPrivatePtr priv = vm->privateData;
-    virCgroupPtr cgroup_temp = NULL;
+    qemuCgroupEmulatorAllNodesDataPtr emulatorCgroup = NULL;
-    char *mem_mask = NULL;
-    char *all_nodes_str = NULL;
-    virBitmapPtr all_nodes = NULL;
-    virErrorPtr err = NULL;
     virBitmapPtr vcpumap = NULL;
     ssize_t nextvcpu = -1;
     int rc = 0;
@@ -4866,22 +4862,8 @@ qemuDomainSetVcpusLive(virQEMUDriverPtr driver,
     if (!(vcpumap = qemuDomainSelectHotplugVcpuEntities(vm->def, nvcpus)))
         goto cleanup;
 
-    if (virNumaIsAvailable() &&
+    if (qemuCgroupEmulatorAllNodesAllow(priv->cgroup, &emulatorCgroup) < 0)
-        virCgroupHasController(priv->cgroup, VIR_CGROUP_CONTROLLER_CPUSET)) {
+        goto cleanup;
-        if (virCgroupNewThread(priv->cgroup, VIR_CGROUP_THREAD_EMULATOR, 0,
-                               false, &cgroup_temp) < 0)
-            goto cleanup;
-
-        if (!(all_nodes = virNumaGetHostNodeset()))
-            goto cleanup;
-
-        if (!(all_nodes_str = virBitmapFormat(all_nodes)))
-            goto cleanup;
-
-        if (virCgroupGetCpusetMems(cgroup_temp, &mem_mask) < 0 ||
-            virCgroupSetCpusetMems(cgroup_temp, all_nodes_str) < 0)
-            goto cleanup;
-    }
 
     if (nvcpus > virDomainDefGetVcpus(vm->def)) {
         while ((nextvcpu = virBitmapNextSetBit(vcpumap, nextvcpu)) != -1) {
@@ -4909,17 +4891,7 @@ qemuDomainSetVcpusLive(virQEMUDriverPtr driver,
     ret = 0;
 
  cleanup:
-    if (mem_mask) {
+    qemuCgrouEmulatorAllNodesRestore(emulatorCgroup);
-        err = virSaveLastError();
-        virCgroupSetCpusetMems(cgroup_temp, mem_mask);
-        virSetError(err);
-        virFreeError(err);
-        VIR_FREE(mem_mask);
-    }
-
-    VIR_FREE(all_nodes_str);
-    virBitmapFree(all_nodes);
-    virCgroupFree(&cgroup_temp);
     virBitmapFree(vcpumap);
 
     return ret;