diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 77f51d9a03074d09b9e33fe91fa65d6ae5d3862a..e0b672357f3075e4e564a5e76cb2763eb77e4c1d 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -16278,9 +16278,6 @@ qemuDomainBlockJobImpl(virDomainObjPtr vm,
         goto endjob;
 
     if (baseSource) {
-        if (qemuGetDriveSourceString(baseSource, NULL, &basePath) < 0)
-            goto endjob;
-
         if (flags & VIR_DOMAIN_BLOCK_REBASE_RELATIVE) {
             if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_CHANGE_BACKING_FILE)) {
                 virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
@@ -16318,8 +16315,12 @@ qemuDomainBlockJobImpl(virDomainObjPtr vm,
     }
 
     qemuDomainObjEnterMonitor(driver, vm);
-    ret = qemuMonitorBlockJob(priv->mon, device, basePath, backingPath,
-                              speed, mode, async);
+    if (baseSource)
+        basePath = qemuMonitorDiskNameLookup(priv->mon, device, disk->src,
+                                             baseSource);
+    if (!baseSource || basePath)
+        ret = qemuMonitorBlockJob(priv->mon, device, basePath, backingPath,
+                                  speed, mode, async);
     if (qemuDomainObjExitMonitor(driver, vm) < 0)
         ret = -1;
     if (ret < 0) {
@@ -17045,12 +17046,6 @@ 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)) {
@@ -17081,9 +17076,14 @@ qemuDomainBlockCommit(virDomainPtr dom,
         disk->mirrorJob = VIR_DOMAIN_BLOCK_JOB_TYPE_ACTIVE_COMMIT;
     }
     qemuDomainObjEnterMonitor(driver, vm);
-    ret = qemuMonitorBlockCommit(priv->mon, device,
-                                 topPath, basePath, backingPath,
-                                 speed);
+    basePath = qemuMonitorDiskNameLookup(priv->mon, device, disk->src,
+                                         baseSource);
+    topPath = qemuMonitorDiskNameLookup(priv->mon, device, disk->src,
+                                        topSource);
+    if (basePath && topPath)
+        ret = qemuMonitorBlockCommit(priv->mon, device,
+                                     topPath, basePath, backingPath,
+                                     speed);
     if (qemuDomainObjExitMonitor(driver, vm) < 0) {
         ret = -1;
         goto endjob;
diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
index 18f866fa7ed8dfe9aa9927df1ea1da495b824f18..e0a9fe9b3a989af67c81b9617ee5cd88f2687636 100644
--- a/src/qemu/qemu_monitor.c
+++ b/src/qemu/qemu_monitor.c
@@ -3471,6 +3471,24 @@ qemuMonitorSupportsActiveCommit(qemuMonitorPtr mon)
 }
 
 
+/* Determine the name that qemu is using for tracking the backing
+ * element TARGET within the chain starting at TOP.  */
+char *
+qemuMonitorDiskNameLookup(qemuMonitorPtr mon,
+                          const char *device,
+                          virStorageSourcePtr top,
+                          virStorageSourcePtr target)
+{
+    if (!mon->json) {
+        virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
+                       _("JSON monitor is required"));
+        return NULL;
+    }
+
+    return qemuMonitorJSONDiskNameLookup(mon, device, top, target);
+}
+
+
 /* Use the block-job-complete monitor command to pivot a block copy
  * job.  */
 int
diff --git a/src/qemu/qemu_monitor.h b/src/qemu/qemu_monitor.h
index b30da34c4ebe699d2c5ac163b562a195e7a6fbe8..e67d80098ec8021d52c2d91259a94ed66bbc841a 100644
--- a/src/qemu/qemu_monitor.h
+++ b/src/qemu/qemu_monitor.h
@@ -1,7 +1,7 @@
 /*
  * qemu_monitor.h: interaction with QEMU monitor console
  *
- * Copyright (C) 2006-2014 Red Hat, Inc.
+ * Copyright (C) 2006-2015 Red Hat, Inc.
  * Copyright (C) 2006 Daniel P. Berrange
  *
  * This library is free software; you can redistribute it and/or
@@ -734,6 +734,12 @@ int qemuMonitorBlockCommit(qemuMonitorPtr mon,
     ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(3)
     ATTRIBUTE_NONNULL(4);
 bool qemuMonitorSupportsActiveCommit(qemuMonitorPtr mon);
+char *qemuMonitorDiskNameLookup(qemuMonitorPtr mon,
+                                const char *device,
+                                virStorageSourcePtr top,
+                                virStorageSourcePtr target)
+    ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(3)
+    ATTRIBUTE_NONNULL(4);
 
 int qemuMonitorArbitraryCommand(qemuMonitorPtr mon,
                                 const char *cmd,
diff --git a/src/qemu/qemu_monitor_json.c b/src/qemu/qemu_monitor_json.c
index c16f3caeb338ac01d93c98228fc18d89d7281601..8994d5a30867535e8c1fc1f650c86478837eb2c8 100644
--- a/src/qemu/qemu_monitor_json.c
+++ b/src/qemu/qemu_monitor_json.c
@@ -1,7 +1,7 @@
 /*
  * qemu_monitor_json.c: interaction with QEMU monitor console
  *
- * Copyright (C) 2006-2014 Red Hat, Inc.
+ * Copyright (C) 2006-2015 Red Hat, Inc.
  * Copyright (C) 2006 Daniel P. Berrange
  *
  * This library is free software; you can redistribute it and/or
@@ -3883,6 +3883,106 @@ qemuMonitorJSONDrivePivot(qemuMonitorPtr mon, const char *device,
 }
 
 
+static char *
+qemuMonitorJSONDiskNameLookupOne(virJSONValuePtr image,
+                                 virStorageSourcePtr top,
+                                 virStorageSourcePtr target)
+{
+    virJSONValuePtr backing;
+    char *ret;
+
+    /* The caller will report a generic message if we return NULL
+     * without an error; but in some cases we can improve by reporting
+     * a more specific message.  */
+    if (!top || !image)
+        return NULL;
+    if (top != target) {
+        backing = virJSONValueObjectGet(image, "backing-image");
+        return qemuMonitorJSONDiskNameLookupOne(backing, top->backingStore,
+                                                target);
+    }
+    if (VIR_STRDUP(ret, virJSONValueObjectGetString(image, "filename")) < 0)
+        return NULL;
+    /* Sanity check - the name qemu gave us should resolve to the same
+       file tracked by our target description. */
+    if (virStorageSourceIsLocalStorage(target) &&
+        STRNEQ(ret, target->path) &&
+        !virFileLinkPointsTo(ret, target->path)) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("qemu block name '%s' doesn't match expected '%s'"),
+                       ret, target->path);
+        VIR_FREE(ret);
+    }
+    return ret;
+}
+
+
+char *
+qemuMonitorJSONDiskNameLookup(qemuMonitorPtr mon,
+                              const char *device,
+                              virStorageSourcePtr top,
+                              virStorageSourcePtr target)
+{
+    char *ret = NULL;
+    virJSONValuePtr cmd = NULL;
+    virJSONValuePtr reply = NULL;
+    virJSONValuePtr devices;
+    size_t i;
+
+    cmd = qemuMonitorJSONMakeCommand("query-block", NULL);
+    if (!cmd)
+        return NULL;
+    if (qemuMonitorJSONCommand(mon, cmd, &reply) < 0)
+        goto cleanup;
+
+    devices = virJSONValueObjectGet(reply, "return");
+    if (!devices || devices->type != VIR_JSON_TYPE_ARRAY) {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("block info reply was missing device list"));
+        goto cleanup;
+    }
+
+    for (i = 0; i < virJSONValueArraySize(devices); i++) {
+        virJSONValuePtr dev = virJSONValueArrayGet(devices, i);
+        virJSONValuePtr inserted;
+        virJSONValuePtr image;
+        const char *thisdev;
+
+        if (!dev || dev->type != VIR_JSON_TYPE_OBJECT) {
+            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                           _("block info device entry was not in expected format"));
+            goto cleanup;
+        }
+
+        if (!(thisdev = virJSONValueObjectGetString(dev, "device"))) {
+            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                           _("block info device entry was not in expected format"));
+            goto cleanup;
+        }
+
+        if (STREQ(thisdev, device)) {
+            if ((inserted = virJSONValueObjectGet(dev, "inserted")) &&
+                (image = virJSONValueObjectGet(inserted, "image"))) {
+                ret = qemuMonitorJSONDiskNameLookupOne(image, top, target);
+            }
+            break;
+        }
+    }
+    /* Guarantee an error when returning NULL, but don't override a
+     * more specific error if one was already generated.  */
+    if (!ret && !virGetLastError())
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("unable to find backing name for device %s"),
+                       device);
+
+ cleanup:
+    virJSONValueFree(cmd);
+    virJSONValueFree(reply);
+
+    return ret;
+}
+
+
 int qemuMonitorJSONArbitraryCommand(qemuMonitorPtr mon,
                                     const char *cmd_str,
                                     char **reply_str,
diff --git a/src/qemu/qemu_monitor_json.h b/src/qemu/qemu_monitor_json.h
index 8ceea8a1889a1dfce16dcf207a637026dfdaf6ed..49392b61e8ed1074f6603dc3bb9ae0a39693421b 100644
--- a/src/qemu/qemu_monitor_json.h
+++ b/src/qemu/qemu_monitor_json.h
@@ -1,7 +1,7 @@
 /*
  * qemu_monitor_json.h: interaction with QEMU monitor console
  *
- * Copyright (C) 2006-2009, 2011-2014 Red Hat, Inc.
+ * Copyright (C) 2006-2009, 2011-2015 Red Hat, Inc.
  * Copyright (C) 2006 Daniel P. Berrange
  *
  * This library is free software; you can redistribute it and/or
@@ -277,6 +277,13 @@ int qemuMonitorJSONBlockCommit(qemuMonitorPtr mon,
                                unsigned long long bandwidth)
     ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2);
 
+char *qemuMonitorJSONDiskNameLookup(qemuMonitorPtr mon,
+                                    const char *device,
+                                    virStorageSourcePtr top,
+                                    virStorageSourcePtr target)
+    ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(3)
+    ATTRIBUTE_NONNULL(4);
+
 int qemuMonitorJSONArbitraryCommand(qemuMonitorPtr mon,
                                     const char *cmd_str,
                                     char **reply_str,