qemu: Add support for networked disks for block commit

Now that we are able to select images from the backing chain via indexed
access we should also convert possible network sources to
qemu-compatible strings before passing them to qemu.

src/qemu/qemu_driver.c

@@ -15505,9 +15505,13 @@ qemuDomainBlockCommit(virDomainPtr dom,
     unsigned int baseIndex = 0;
     const char *top_parent = NULL;
     bool clean_access = false;
+    char *topPath = NULL;
+    char *basePath = NULL;
+    char *backingPath = NULL;
 
     /* XXX Add support for COMMIT_ACTIVE, COMMIT_DELETE */
-    virCheckFlags(VIR_DOMAIN_BLOCK_COMMIT_SHALLOW, -1);
+    virCheckFlags(VIR_DOMAIN_BLOCK_COMMIT_SHALLOW |
+                  VIR_DOMAIN_BLOCK_COMMIT_RELATIVE, -1);
 
     if (!(vm = qemuDomObjFromDomain(dom)))
         goto cleanup;
@@ -15617,6 +15621,31 @@ qemuDomainBlockCommit(virDomainPtr dom,
                                                VIR_DISK_CHAIN_READ_WRITE) < 0))
         goto endjob;
 
+    if (qemuGetDriveSourceString(topSource, NULL, &topPath) < 0)
+        goto endjob;
+
+    if (qemuGetDriveSourceString(baseSource, NULL, &basePath) < 0)
+        goto endjob;
+
+    if (flags & VIR_DOMAIN_BLOCK_COMMIT_RELATIVE &&
+        topSource != disk->src) {
+        if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_CHANGE_BACKING_FILE)) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("this qemu doesn't support relative blockpull"));
+            goto endjob;
+        }
+
+        if (virStorageFileGetRelativeBackingPath(topSource, baseSource,
+                                                 &backingPath) < 0)
+            goto endjob;
+
+        if (!backingPath) {
+            virReportError(VIR_ERR_OPERATION_INVALID, "%s",
+                           _("can't keep relative backing relationship"));
+            goto endjob;
+        }
+    }
+
     /* Start the commit operation.  Pass the user's original spelling,
      * if any, through to qemu, since qemu may behave differently
      * depending on whether the input was specified as relative or
@@ -15624,9 +15653,7 @@ qemuDomainBlockCommit(virDomainPtr dom,
      * thing if the user specified a relative name). */
     qemuDomainObjEnterMonitor(driver, vm);
     ret = qemuMonitorBlockCommit(priv->mon, device,
-                                 top && !topIndex ? top : topSource->path,
-                                 base && !baseIndex ? base : baseSource->path,
-                                 NULL,
+                                 topPath, basePath, backingPath,
                                  bandwidth);
     qemuDomainObjExitMonitor(driver, vm);
 
@@ -15644,6 +15671,9 @@ qemuDomainBlockCommit(virDomainPtr dom,
         vm = NULL;
 
  cleanup:
+    VIR_FREE(topPath);
+    VIR_FREE(basePath);
+    VIR_FREE(backingPath);
     VIR_FREE(device);
     if (vm)
         virObjectUnlock(vm);