qemuBuildMemoryBackendStr: Reorder args and update comment

Frankly, this function is one big mess. A lot of arguments,
complicated behaviour. It's really surprising that arguments were
in random order (input and output arguments were mixed together),
the documentation was outdated, the description of return values
was bogus.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_command.c

@@ -3177,31 +3177,38 @@ qemuBuildControllerDevCommandLine(virCommandPtr cmd,
 
 /**
  * qemuBuildMemoryBackendStr:
- * @mem: memory definition object
- * @autoNodeset: fallback nodeset in case of automatic numa placement
- * @def: domain definition object
- * @qemuCaps: qemu capabilities object
+ * @backendProps: [out] constructed object
+ * @backendType: [out] type of the backennd used
  * @cfg: qemu driver config object
- * @aliasPrefix: prefix string of the alias (to allow for multiple frontents)
- * @id: index of the device (to construct the alias)
- * @backendStr: returns the object string
+ * @qemuCaps: qemu capabilities object
+ * @def: domain definition object
+ * @mem: memory definition object
+ * @autoNodeset: fallback nodeset in case of automatic NUMA placement
+ * @force: forcibly use one of the backends
  *
- * Formats the configuration string for the memory device backend according
- * to the configuration. @pagesize and @hostNodes can be used to override the
- * default source configuration, both are optional.
+ * Creates a configuration object that represents memory backend of given guest
+ * NUMA node (domain @def and @mem). Use @autoNodeset to fine tune the
+ * placement of the memory on the host NUMA nodes.
  *
- * Returns 0 on success, 1 if only the implicit memory-device-ram with no
- * other configuration was used (to detect legacy configurations). Returns
- * -1 in case of an error.
+ * By default, if no memory-backend-* object is necessary to fulfil the guest
+ * configuration value of 1 is returned. This behaviour can be suppressed by
+ * setting @force to true in which case 0 would be returned.
+ *
+ * Then, if one of the two memory-backend-* should be used, the @qemuCaps is
+ * consulted to check if qemu does support it.
+ *
+ * Returns: 0 on success,
+ *          1 on success and if there's no need to use memory-backend-*
+ *         -1 on error.
  */
 int
-qemuBuildMemoryBackendStr(virDomainMemoryDefPtr mem,
-                          virBitmapPtr autoNodeset,
-                          virDomainDefPtr def,
-                          virQEMUCapsPtr qemuCaps,
-                          virQEMUDriverConfigPtr cfg,
+qemuBuildMemoryBackendStr(virJSONValuePtr *backendProps,
                           const char **backendType,
-                          virJSONValuePtr *backendProps,
+                          virQEMUDriverConfigPtr cfg,
+                          virQEMUCapsPtr qemuCaps,
+                          virDomainDefPtr def,
+                          virDomainMemoryDefPtr mem,
+                          virBitmapPtr autoNodeset,
                           bool force)
 {
     virDomainHugePagePtr master_hugepage = NULL;
@@ -3425,8 +3432,8 @@ qemuBuildMemoryCellBackendStr(virDomainDefPtr def,
     if (virAsprintf(&alias, "ram-node%zu", cell) < 0)
         goto cleanup;
 
-    if ((rc = qemuBuildMemoryBackendStr(&mem, auto_nodeset, def, qemuCaps,
-                                        cfg, &backendType, &props, false)) < 0)
+    if ((rc = qemuBuildMemoryBackendStr(&props, &backendType, cfg, qemuCaps,
+                                        def, &mem, auto_nodeset, false)) < 0)
         goto cleanup;
 
     if (!(*backendStr = virQEMUBuildObjectCommandlineFromJSON(backendType,
@@ -3465,9 +3472,8 @@ qemuBuildMemoryDimmBackendStr(virDomainMemoryDefPtr mem,
     if (virAsprintf(&alias, "mem%s", mem->info.alias) < 0)
         goto cleanup;
 
-    if (qemuBuildMemoryBackendStr(mem, auto_nodeset,
-                                  def, qemuCaps, cfg,
-                                  &backendType, &props, true) < 0)
+    if (qemuBuildMemoryBackendStr(&props, &backendType, cfg, qemuCaps,
+                                  def, mem, auto_nodeset, true) < 0)
         goto cleanup;
 
     ret = virQEMUBuildObjectCommandlineFromJSON(backendType, alias, props);

src/qemu/qemu_command.h

@@ -124,13 +124,13 @@ char *qemuBuildControllerDevStr(const virDomainDef *domainDef,
                                 virQEMUCapsPtr qemuCaps,
                                 int *nusbcontroller);
 
-int qemuBuildMemoryBackendStr(virDomainMemoryDefPtr mem,
-                              virBitmapPtr autoNodeset,
-                              virDomainDefPtr def,
-                              virQEMUCapsPtr qemuCaps,
-                              virQEMUDriverConfigPtr cfg,
+int qemuBuildMemoryBackendStr(virJSONValuePtr *backendProps,
                               const char **backendType,
-                              virJSONValuePtr *backendProps,
+                              virQEMUDriverConfigPtr cfg,
+                              virQEMUCapsPtr qemuCaps,
+                              virDomainDefPtr def,
+                              virDomainMemoryDefPtr mem,
+                              virBitmapPtr autoNodeset,
                               bool force);
 
 char *qemuBuildMemoryDeviceStr(virDomainMemoryDefPtr mem);

src/qemu/qemu_hotplug.c

@@ -2240,8 +2240,8 @@ qemuDomainAttachMemory(virQEMUDriverPtr driver,
     if (!(devstr = qemuBuildMemoryDeviceStr(mem)))
         goto cleanup;
 
-    if (qemuBuildMemoryBackendStr(mem, NULL, vm->def, priv->qemuCaps,
-                                  cfg, &backendType, &props, true) < 0)
+    if (qemuBuildMemoryBackendStr(&props, &backendType, cfg,
+                                  priv->qemuCaps, vm->def, mem, NULL, true) < 0)
         goto cleanup;
 
     if (virDomainMemoryInsert(vm->def, mem) < 0) {