storage: rbd: qemu: Add support for specifying internal RBD snapshots

Some storage systems have internal support for snapshots. Libvirt should
be able to select a correct snapshot when starting a VM.

This patch adds a XML element to select a storage source snapshot for
the RBD protocol which supports this feature.

docs/formatdomain.html.in

@@ -1679,6 +1679,7 @@
       <driver name="qemu" type="raw"/>
       <source protocol="rbd" name="image_name2">
         <host name="hostname" port="7000"/>
+        <snapshot name="snapname"/>
       </source>
       <target dev="hdc" bus="ide"/>
       <auth username='myuser'>
@@ -1952,15 +1953,17 @@
         is only valid when the specified storage volume is of 'file' or
         'block' type).
         <p>
-        When the disk <code>type</code> is "network", the <code>source</code>
-        may have zero or more <code>host</code> sub-elements used to
-        specify the hosts to connect.
+        The <code>source</code> element may contain the following sub elements:
         </p>
 
         <dl>
           <dt><code>host</code></dt>
           <dd>
             <p>
+            When the disk <code>type</code> is "network", the <code>source</code>
+            may have zero or more <code>host</code> sub-elements used to
+            specify the hosts to connect.
+
             The <code>host</code> element supports 4 attributes, viz.  "name",
             "port", "transport" and "socket", which specify the hostname,
             the port number, transport type and path to socket, respectively.
@@ -2013,6 +2016,13 @@
             AF_UNIX socket.
             </p>
           </dd>
+          <dt><code>snapshot</code></dt>
+          <dd>
+            The <code>name</code> attribute of <code>snapshot</code> element can
+            optionally specify an internal snapshot name to be used as the
+            source for storage protocols.
+            Supported for 'rbd' <span class="since">since 1.2.11 (QEMU only).</span>
+          </dd>
         </dl>
 
         <p>

docs/schemas/domaincommon.rng

@@ -1452,6 +1452,14 @@
             </choice>
           </element>
         </zeroOrMore>
+        <optional>
+          <element name="snapshot">
+            <attribute name="name">
+              <ref name="genericName"/>
+            </attribute>
+            <empty/>
+          </element>
+        </optional>
         <empty/>
       </element>
     </interleave>

src/conf/domain_conf.c

@@ -3165,6 +3165,22 @@ virDomainDeviceDefPostParseInternal(virDomainDeviceDefPtr dev,
             return -1;
     }
 
+    /* verify disk source */
+    if (dev->type == VIR_DOMAIN_DEVICE_DISK) {
+        virDomainDiskDefPtr disk = dev->data.disk;
+
+        /* internal snapshots are currently supported only with rbd: */
+        if (virStorageSourceGetActualType(disk->src) != VIR_STORAGE_TYPE_NETWORK &&
+            disk->src->protocol != VIR_STORAGE_NET_PROTOCOL_RBD) {
+            if (disk->src->snapshot) {
+                virReportError(VIR_ERR_XML_ERROR, "%s",
+                               _("<snapshot> element is currently supported "
+                                 "only with 'rbd' disks"));
+                return -1;
+            }
+        }
+    }
+
     return 0;
 }
 
@@ -5316,10 +5332,14 @@ virDomainDiskSourcePoolDefParse(xmlNodePtr node,
 
 int
 virDomainDiskSourceParse(xmlNodePtr node,
+                         xmlXPathContextPtr ctxt,
                          virStorageSourcePtr src)
 {
     int ret = -1;
     char *protocol = NULL;
+    xmlNodePtr saveNode = ctxt->node;
+
+    ctxt->node = node;
 
     switch ((virStorageType)src->type) {
     case VIR_STORAGE_TYPE_FILE:
@@ -5372,6 +5392,9 @@ virDomainDiskSourceParse(xmlNodePtr node,
             tmp[0] = '\0';
         }
 
+        /* snapshot currently works only for remote disks */
+        src->snapshot = virXPathString("string(./snapshot/@name)", ctxt);
+
         if (virDomainStorageHostParse(node, &src->hosts, &src->nhosts) < 0)
             goto cleanup;
         break;
@@ -5397,6 +5420,7 @@ virDomainDiskSourceParse(xmlNodePtr node,
 
  cleanup:
     VIR_FREE(protocol);
+    ctxt->node = saveNode;
     return ret;
 }
 
@@ -5452,7 +5476,7 @@ virDomainDiskBackingStoreParse(xmlXPathContextPtr ctxt,
         goto cleanup;
     }
 
-    if (virDomainDiskSourceParse(source, backingStore) < 0 ||
+    if (virDomainDiskSourceParse(source, ctxt, backingStore) < 0 ||
         virDomainDiskBackingStoreParse(ctxt, backingStore) < 0)
         goto cleanup;
 
@@ -5562,7 +5586,7 @@ virDomainDiskDefParseXML(virDomainXMLOptionPtr xmlopt,
                 xmlStrEqual(cur->name, BAD_CAST "source")) {
                 sourceNode = cur;
 
-                if (virDomainDiskSourceParse(cur, def->src) < 0)
+                if (virDomainDiskSourceParse(cur, ctxt, def->src) < 0)
                     goto error;
                 source = def->src->path;
 
@@ -5728,7 +5752,8 @@ virDomainDiskDefParseXML(virDomainXMLOptionPtr xmlopt,
                                        _("mirror requires source element"));
                         goto error;
                     }
-                    if (virDomainDiskSourceParse(mirrorNode, def->mirror) < 0)
+                    if (virDomainDiskSourceParse(mirrorNode, ctxt,
+                                                 def->mirror) < 0)
                         goto error;
                 }
                 ready = virXMLPropString(cur, "ready");
@@ -16142,11 +16167,12 @@ virDomainDiskSourceFormatInternal(virBufferPtr buf,
 
             VIR_FREE(path);
 
-            if (src->nhosts == 0) {
+            if (src->nhosts == 0 && !src->snapshot) {
                 virBufferAddLit(buf, "/>\n");
             } else {
                 virBufferAddLit(buf, ">\n");
                 virBufferAdjustIndent(buf, 2);
+
                 for (n = 0; n < src->nhosts; n++) {
                     virBufferAddLit(buf, "<host");
                     virBufferEscapeString(buf, " name='%s'",
@@ -16163,6 +16189,10 @@ virDomainDiskSourceFormatInternal(virBufferPtr buf,
 
                     virBufferAddLit(buf, "/>\n");
                 }
+
+                virBufferEscapeString(buf, "<snapshot name='%s'/>\n",
+                                      src->snapshot);
+
                 virBufferAdjustIndent(buf, -2);
                 virBufferAddLit(buf, "</source>\n");
             }

src/conf/domain_conf.h

@@ -2492,6 +2492,7 @@ virDomainDiskRemove(virDomainDefPtr def, size_t i);
 virDomainDiskDefPtr
 virDomainDiskRemoveByName(virDomainDefPtr def, const char *name);
 int virDomainDiskSourceParse(xmlNodePtr node,
+                             xmlXPathContextPtr ctxt,
                              virStorageSourcePtr src);
 
 bool virDomainHasDiskMirror(virDomainObjPtr vm);

src/conf/snapshot_conf.c

@@ -107,6 +107,7 @@ void virDomainSnapshotDefFree(virDomainSnapshotDefPtr def)
 
 static int
 virDomainSnapshotDiskDefParseXML(xmlNodePtr node,
+                                 xmlXPathContextPtr ctxt,
                                  virDomainSnapshotDiskDefPtr def)
 {
     int ret = -1;
@@ -154,7 +155,7 @@ virDomainSnapshotDiskDefParseXML(xmlNodePtr node,
         if (!def->src->path &&
             xmlStrEqual(cur->name, BAD_CAST "source")) {
 
-            if (virDomainDiskSourceParse(cur, def->src) < 0)
+            if (virDomainDiskSourceParse(cur, ctxt, def->src) < 0)
                 goto cleanup;
 
         } else if (!def->src->format &&
@@ -352,7 +353,8 @@ virDomainSnapshotDefParse(xmlXPathContextPtr ctxt,
             goto cleanup;
         def->ndisks = n;
         for (i = 0; i < def->ndisks; i++) {
-            if (virDomainSnapshotDiskDefParseXML(nodes[i], &def->disks[i]) < 0)
+            if (virDomainSnapshotDiskDefParseXML(nodes[i], ctxt,
+                                                 &def->disks[i]) < 0)
                 goto cleanup;
         }
         VIR_FREE(nodes);

src/qemu/qemu_command.c

@@ -2983,6 +2983,9 @@ qemuBuildNetworkDriveURI(virStorageSourcePtr src,
 
             virBufferStrcat(&buf, "rbd:", src->path, NULL);
 
+            if (src->snapshot)
+                virBufferEscape(&buf, '\\', ":", "@%s", src->snapshot);
+
             if (username) {
                 virBufferEscape(&buf, '\\', ":", ":id=%s", username);
                 virBufferEscape(&buf, '\\', ":",

src/util/virstoragefile.c

@@ -1848,6 +1848,7 @@ virStorageSourceCopy(const virStorageSource *src,
         VIR_STRDUP(ret->driverName, src->driverName) < 0 ||
         VIR_STRDUP(ret->relPath, src->relPath) < 0 ||
         VIR_STRDUP(ret->backingStoreRaw, src->backingStoreRaw) < 0 ||
+        VIR_STRDUP(ret->snapshot, src->snapshot) < 0 ||
         VIR_STRDUP(ret->compat, src->compat) < 0)
         goto error;
 
@@ -2280,6 +2281,13 @@ virStorageSourceParseRBDColonString(const char *rbdstr,
         *p = '\0';
     }
 
+    /* snapshot name */
+    if ((p = strchr(src->path, '@'))) {
+        if (VIR_STRDUP(src->snapshot, p + 1) < 0)
+            goto error;
+        *p = '\0';
+    }
+
     /* options */
     if (!options)
         return 0; /* all done */

src/util/virstoragefile.h

@@ -238,6 +238,7 @@ struct _virStorageSource {
     char *path;
     int protocol; /* virStorageNetProtocol */
     char *volume; /* volume name for remote storage */
+    char *snapshot; /* for storage systems supporting internal snapshots */
     size_t nhosts;
     virStorageNetHostDefPtr hosts;
     virStorageSourcePoolDefPtr srcpool;

tests/qemuxml2argvdata/qemuxml2argv-disk-drive-network-rbd.args

@@ -5,4 +5,8 @@ unix:/tmp/test-monitor,server,nowait -no-acpi -boot c -usb \
 -drive 'file=rbd:pool/image:auth_supported=none:\
 mon_host=mon1.example.org\:6321\;mon2.example.org\:6322\;\
 mon3.example.org\:6322,if=virtio,format=raw' \
+-drive file=rbd:pool/image@asdf:auth_supported=none,if=virtio,format=raw \
+-drive 'file=rbd:pool/image@foo:auth_supported=none:\
+mon_host=mon1.example.org\:6321\;mon2.example.org\:6322\;\
+mon3.example.org\:6322,if=virtio,format=raw' \
 -net none -serial none -parallel none

tests/qemuxml2argvdata/qemuxml2argv-disk-drive-network-rbd.xml

@@ -29,6 +29,23 @@
       </source>
       <target dev='vda' bus='virtio'/>
     </disk>
+    <disk type='network' device='disk'>
+      <driver name='qemu' type='raw'/>
+      <source protocol='rbd' name='pool/image'>
+        <snapshot name='asdf'/>
+      </source>
+      <target dev='vdb' bus='virtio'/>
+    </disk>
+    <disk type='network' device='disk'>
+      <driver name='qemu' type='raw'/>
+      <source protocol='rbd' name='pool/image'>
+        <host name='mon1.example.org' port='6321'/>
+        <host name='mon2.example.org' port='6322'/>
+        <host name='mon3.example.org' port='6322'/>
+        <snapshot name='foo'/>
+      </source>
+      <target dev='vdc' bus='virtio'/>
+    </disk>
     <controller type='usb' index='0'/>
     <controller type='ide' index='0'/>
     <controller type='pci' index='0' model='pci-root'/>