virsh: add snapshot backing store support to vol-create-as

This patch adds two new parameters to the vol-create-as command:

 --backing-vol <volume-name-or-key-or-path>
 --backing-vol-format <format-of-backing-vol>

  virsh # vol-create-as guest_images_lvm snapvol1 5G --backing-vol \
              rhel6vm1lun1
  Vol snapvol1 created

  virsh # vol-create-as image_dir qcow2snap2 5G --format qcow2 \
              --backing-vol imagevol1.qcow2 \
              --backing-vol-format qcow2
  Vol qcow2snap2 created

Additionally, the virsh man page update fixes incorrect snapshot
parameters that were included in my prior bulk volume command patch.

tools/virsh.c

@@ -5279,6 +5279,8 @@ static const vshCmdOptDef opts_vol_create_as[] = {
     {"capacity", VSH_OT_DATA, VSH_OFLAG_REQ, N_("size of the vol with optional k,M,G,T suffix")},
     {"allocation", VSH_OT_STRING, 0, N_("initial allocation size with optional k,M,G,T suffix")},
     {"format", VSH_OT_STRING, 0, N_("file format type raw,bochs,qcow,qcow2,vmdk")},
+    {"backing-vol", VSH_OT_STRING, 0, N_("the backing volume if taking a snapshot")},
+    {"backing-vol-format", VSH_OT_STRING, 0, N_("format of backing volume if taking a snapshot")},
     {NULL, 0, 0, NULL}
 };
 
@@ -5318,6 +5320,7 @@ cmdVolCreateAs(vshControl *ctl, const vshCmd *cmd)
     int found;
     char *xml;
     char *name, *capacityStr, *allocationStr, *format;
+    char *snapshotStrVol, *snapshotStrFormat;
     unsigned long long capacity, allocation = 0;
     virBuffer buf = VIR_BUFFER_INITIALIZER;
 
@@ -5344,6 +5347,8 @@ cmdVolCreateAs(vshControl *ctl, const vshCmd *cmd)
         vshError(ctl, _("Malformed size %s"), allocationStr);
 
     format = vshCommandOptString(cmd, "format", &found);
+    snapshotStrVol = vshCommandOptString(cmd, "backing-vol", &found);
+    snapshotStrFormat = vshCommandOptString(cmd, "backing-vol-format", &found);
 
     virBufferAddLit(&buf, "<volume>\n");
     virBufferVSprintf(&buf, "  <name>%s</name>\n", name);
@@ -5356,8 +5361,62 @@ cmdVolCreateAs(vshControl *ctl, const vshCmd *cmd)
         virBufferVSprintf(&buf, "    <format type='%s'/>\n",format);
         virBufferAddLit(&buf, "  </target>\n");
     }
-    virBufferAddLit(&buf, "</volume>\n");
 
+    /* Convert the snapshot parameters into backingStore XML */
+    if (snapshotStrVol) {
+        /* Lookup snapshot backing volume.  Try the backing-vol
+         *  parameter as a name */
+        vshDebug(ctl, 5, "%s: Look up backing store volume '%s' as name\n",
+                 cmd->def->name, snapshotStrVol);
+        virStorageVolPtr snapVol = virStorageVolLookupByName(pool, snapshotStrVol);
+        if (snapVol)
+                vshDebug(ctl, 5, "%s: Backing store volume found using '%s' as name\n",
+                         cmd->def->name, snapshotStrVol);
+
+        if (snapVol == NULL) {
+            /* Snapshot backing volume not found by name.  Try the
+             *  backing-vol parameter as a key */
+            vshDebug(ctl, 5, "%s: Look up backing store volume '%s' as key\n",
+                     cmd->def->name, snapshotStrVol);
+            snapVol = virStorageVolLookupByKey(ctl->conn, snapshotStrVol);
+            if (snapVol)
+                vshDebug(ctl, 5, "%s: Backing store volume found using '%s' as key\n",
+                         cmd->def->name, snapshotStrVol);
+        }
+        if (snapVol == NULL) {
+            /* Snapshot backing volume not found by key.  Try the
+             *  backing-vol parameter as a path */
+            vshDebug(ctl, 5, "%s: Look up backing store volume '%s' as path\n",
+                     cmd->def->name, snapshotStrVol);
+            snapVol = virStorageVolLookupByPath(ctl->conn, snapshotStrVol);
+            if (snapVol)
+                vshDebug(ctl, 5, "%s: Backing store volume found using '%s' as path\n",
+                         cmd->def->name, snapshotStrVol);
+        }
+        if (snapVol == NULL) {
+            vshError(ctl, _("failed to get vol '%s'"), snapshotStrVol);
+            return FALSE;
+        }
+
+        char *snapshotStrVolPath;
+        if ((snapshotStrVolPath = virStorageVolGetPath(snapVol)) == NULL) {
+            virStorageVolFree(snapVol);
+            return FALSE;
+        }
+
+        /* Create XML for the backing store */
+        virBufferAddLit(&buf, "  <backingStore>\n");
+        virBufferVSprintf(&buf, "    <path>%s</path>\n",snapshotStrVolPath);
+        if (snapshotStrFormat)
+            virBufferVSprintf(&buf, "    <format type='%s'/>\n",snapshotStrFormat);
+        virBufferAddLit(&buf, "  </backingStore>\n");
+
+        /* Cleanup snapshot allocations */
+        VIR_FREE(snapshotStrVolPath);
+        virStorageVolFree(snapVol);
+    }
+
+    virBufferAddLit(&buf, "</volume>\n");
 
     if (virBufferError(&buf)) {
         vshPrint(ctl, "%s", _("Failed to allocate XML buffer"));

tools/virsh.pod

@@ -784,8 +784,8 @@ source volume is in.
 I<vol-name-or-key-or-path> is the name or key or path of the source volume.
 
 =item B<vol-create-as> I<pool-or-uuid> I<name> I<capacity> optional
-I<--allocation> I<size> I<--format> I<string> I<--snapshot-source-vol>
-I<vol-name-or-key-or-path> I<--snapshot-source-format> I<string>
+I<--allocation> I<size> I<--format> I<string> I<--backing-vol>
+I<vol-name-or-key-or-path> I<--backing-vol-format> I<string>
 
 Create a volume from a set of arguments.
 I<pool-or-uuid> is the name or UUID of the storage pool to create the volume
@@ -797,10 +797,10 @@ I<--allocation> I<size> is the initial size to be allocated in the volume, with
 optional k, M, G, or T suffix.
 I<--format> I<string> is used in file based storage pools to specify the volume
 file format to use; raw, bochs, qcow, qcow2, vmdk.
-I<--snapshot-source-vol> I<vol-name-or-key-or-path> is the source backing
+I<--backing-vol> I<vol-name-or-key-or-path> is the source backing
 volume to be used if taking a snapshot of an existing volume.
-I<--snapshot-source-format> I<string> is the format of the snapshot backing volume;
-raw, bochs, qcow, qcow2, vmdk.
+I<--backing-vol-format> I<string> is the format of the snapshot backing volume;
+raw, bochs, qcow, qcow2, vmdk, host_device.
 
 =item B<vol-clone> [optional I<--pool> I<pool-or-uuid>] I<vol-name-or-key-or-path> I<name>