storage: allow metadata preallocation when creating qcow2 images

Add VIR_STORAGE_VOL_CREATE_PREALLOC_METADATA flag to virStorageVolCreateXML
and virStorageVolCreateXMLFrom. This flag requests metadata
preallocation when creating/cloning qcow2 images, resulting in creating
a sparse file with qcow2 metadata. It has only slightly larger disk usage
compared to new image with no allocation, but offers higher performance.

include/libvirt/libvirt.h.in

@@ -2906,6 +2906,10 @@ virStorageVolPtr        virStorageVolLookupByPath       (virConnectPtr conn,
 const char*             virStorageVolGetName            (virStorageVolPtr vol);
 const char*             virStorageVolGetKey             (virStorageVolPtr vol);
 
+typedef enum {
+    VIR_STORAGE_VOL_CREATE_PREALLOC_METADATA = 1 << 0,
+} virStorageVolCreateFlags;
+
 virStorageVolPtr        virStorageVolCreateXML          (virStoragePoolPtr pool,
                                                          const char *xmldesc,
                                                          unsigned int flags);

src/libvirt.c

@@ -13382,11 +13382,16 @@ virStorageVolGetKey(virStorageVolPtr vol)
  * virStorageVolCreateXML:
  * @pool: pointer to storage pool
  * @xmlDesc: description of volume to create
- * @flags: extra flags; not used yet, so callers should always pass 0
+ * @flags: bitwise-OR of virStorageVolCreateFlags
  *
  * Create a storage volume within a pool based
  * on an XML description. Not all pools support
- * creation of volumes
+ * creation of volumes.
+ *
+ * Since 1.0.1 VIR_STORAGE_VOL_CREATE_PREALLOC_METADATA
+ * in flags can be used to get higher performance with
+ * qcow2 image files which don't support full preallocation,
+ * by creating a sparse image file with metadata.
  *
  * Returns the storage volume, or NULL on error
  */
@@ -13433,13 +13438,18 @@ error:
  * @pool: pointer to parent pool for the new volume
  * @xmlDesc: description of volume to create
  * @clonevol: storage volume to use as input
- * @flags: extra flags; not used yet, so callers should always pass 0
+ * @flags: bitwise-OR of virStorageVolCreateFlags
  *
  * Create a storage volume in the parent pool, using the
  * 'clonevol' volume as input. Information for the new
  * volume (name, perms)  are passed via a typical volume
  * XML description.
  *
+ * Since 1.0.1 VIR_STORAGE_VOL_CREATE_PREALLOC_METADATA
+ * in flags can be used to get higher performance with
+ * qcow2 image files which don't support full preallocation,
+ * by creating a sparse image file with metadata.
+ *
  * Returns the storage volume, or NULL on error
  */
 virStorageVolPtr

src/storage/storage_backend.c

@@ -668,8 +668,11 @@ virStorageBackendCreateQemuImg(virConnectPtr conn,
     virCommandPtr cmd = NULL;
     bool do_encryption = (vol->target.encryption != NULL);
     unsigned long long int size_arg;
+    bool preallocate = false;
 
-    virCheckFlags(0, -1);
+    virCheckFlags(VIR_STORAGE_VOL_CREATE_PREALLOC_METADATA, -1);
+
+    preallocate = !!(flags & VIR_STORAGE_VOL_CREATE_PREALLOC_METADATA);
 
     const char *type = virStorageFileFormatTypeToString(vol->target.format);
     const char *backingType = vol->backingStore.path ?
@@ -697,11 +700,23 @@ virStorageBackendCreateQemuImg(virConnectPtr conn,
                        inputvol->target.format);
         return -1;
     }
+    if (preallocate && vol->target.format != VIR_STORAGE_FILE_QCOW2) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                       _("metadata preallocation only available with qcow2"));
+        return -1;
+    }
 
     if (vol->backingStore.path) {
         int accessRetCode = -1;
         char *absolutePath = NULL;
 
+        if (preallocate) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("metadata preallocation conflicts with backing"
+                             " store"));
+            return -1;
+        }
+
         /* XXX: Not strictly required: qemu-img has an option a different
          * backing store, not really sure what use it serves though, and it
          * may cause issues with lvm. Untested essentially.
@@ -796,14 +811,15 @@ virStorageBackendCreateQemuImg(virConnectPtr conn,
         virCommandAddArgList(cmd, "convert", "-f", inputType, "-O", type,
                              inputPath, vol->target.path, NULL);
 
-        if (do_encryption) {
+        if (imgformat == QEMU_IMG_BACKING_FORMAT_OPTIONS &&
-            if (imgformat == QEMU_IMG_BACKING_FORMAT_OPTIONS) {
+            (do_encryption || preallocate)) {
-                virCommandAddArgList(cmd, "-o", "encryption=on", NULL);
+            virCommandAddArg(cmd, "-o");
-            } else {
+            virCommandAddArgFormat(cmd, "%s%s%s", do_encryption ? "encryption=on" : "",
-                virCommandAddArg(cmd, "-e");
+                                   (do_encryption && preallocate) ? "," : "",
-            }
+                                   preallocate ? "preallocation=metadata" : "");
+        } else if (do_encryption) {
+            virCommandAddArg(cmd, "-e");
         }
-
     } else if (vol->backingStore.path) {
         virCommandAddArgList(cmd, "create", "-f", type,
                              "-b", vol->backingStore.path, NULL);
@@ -840,12 +856,14 @@ virStorageBackendCreateQemuImg(virConnectPtr conn,
                              vol->target.path, NULL);
         virCommandAddArgFormat(cmd, "%lluK", size_arg);
 
-        if (do_encryption) {
+        if (imgformat == QEMU_IMG_BACKING_FORMAT_OPTIONS &&
-            if (imgformat == QEMU_IMG_BACKING_FORMAT_OPTIONS) {
+            (do_encryption || preallocate)) {
-                virCommandAddArgList(cmd, "-o", "encryption=on", NULL);
+            virCommandAddArg(cmd, "-o");
-            } else {
+            virCommandAddArgFormat(cmd, "%s%s%s", do_encryption ? "encryption=on" : "",
-                virCommandAddArg(cmd, "-e");
+                                   (do_encryption && preallocate) ? "," : "",
-            }
+                                   preallocate ? "preallocation=metadata" : "");
+        } else if (do_encryption) {
+            virCommandAddArg(cmd, "-e");
         }
     }
 

src/storage/storage_backend.h

@@ -37,7 +37,8 @@ typedef int (*virStorageBackendStopPool)(virConnectPtr conn, virStoragePoolObjPt
 typedef int (*virStorageBackendDeletePool)(virConnectPtr conn, virStoragePoolObjPtr pool, unsigned int flags);
 
 typedef int (*virStorageBackendBuildVol)(virConnectPtr conn,
-                                         virStoragePoolObjPtr pool, virStorageVolDefPtr vol);
+                                         virStoragePoolObjPtr pool, virStorageVolDefPtr vol,
+                                         unsigned int flags);
 typedef int (*virStorageBackendCreateVol)(virConnectPtr conn, virStoragePoolObjPtr pool, virStorageVolDefPtr vol);
 typedef int (*virStorageBackendRefreshVol)(virConnectPtr conn, virStoragePoolObjPtr pool, virStorageVolDefPtr vol);
 typedef int (*virStorageBackendDeleteVol)(virConnectPtr conn, virStoragePoolObjPtr pool, virStorageVolDefPtr vol, unsigned int flags);

src/storage/storage_backend_fs.c

@@ -1052,7 +1052,8 @@ static int
 _virStorageBackendFileSystemVolBuild(virConnectPtr conn,
                                      virStoragePoolObjPtr pool,
                                      virStorageVolDefPtr vol,
-                                     virStorageVolDefPtr inputvol)
+                                     virStorageVolDefPtr inputvol,
+                                     unsigned int flags)
 {
     virStorageBackendBuildVolFrom create_func;
     int tool_type;
@@ -1085,7 +1086,7 @@ _virStorageBackendFileSystemVolBuild(virConnectPtr conn,
         return -1;
     }
 
-    if (create_func(conn, pool, vol, inputvol, 0) < 0)
+    if (create_func(conn, pool, vol, inputvol, flags) < 0)
         return -1;
     return 0;
 }
@@ -1098,8 +1099,11 @@ _virStorageBackendFileSystemVolBuild(virConnectPtr conn,
 static int
 virStorageBackendFileSystemVolBuild(virConnectPtr conn,
                                     virStoragePoolObjPtr pool,
-                                    virStorageVolDefPtr vol) {
+                                    virStorageVolDefPtr vol,
-    return _virStorageBackendFileSystemVolBuild(conn, pool, vol, NULL);
+                                    unsigned int flags) {
+    virCheckFlags(VIR_STORAGE_VOL_CREATE_PREALLOC_METADATA, -1);
+
+    return _virStorageBackendFileSystemVolBuild(conn, pool, vol, NULL, flags);
 }
 
 /*
@@ -1112,9 +1116,9 @@ virStorageBackendFileSystemVolBuildFrom(virConnectPtr conn,
                                         virStorageVolDefPtr inputvol,
                                         unsigned int flags)
 {
-    virCheckFlags(0, -1);
+    virCheckFlags(VIR_STORAGE_VOL_CREATE_PREALLOC_METADATA, -1);
 
-    return _virStorageBackendFileSystemVolBuild(conn, pool, vol, inputvol);
+    return _virStorageBackendFileSystemVolBuild(conn, pool, vol, inputvol, flags);
 }
 
 /**

src/storage/storage_driver.c

@@ -1348,7 +1348,7 @@ storageVolumeCreateXML(virStoragePoolPtr obj,
     virStorageVolDefPtr voldef = NULL;
     virStorageVolPtr ret = NULL, volobj = NULL;
 
-    virCheckFlags(0, NULL);
+    virCheckFlags(VIR_STORAGE_VOL_CREATE_PREALLOC_METADATA, NULL);
 
     storageDriverLock(driver);
     pool = virStoragePoolObjFindByUUID(&driver->pools, obj->uuid);
@@ -1425,7 +1425,7 @@ storageVolumeCreateXML(virStoragePoolPtr obj,
         voldef->building = 1;
         virStoragePoolObjUnlock(pool);
 
-        buildret = backend->buildVol(obj->conn, pool, buildvoldef);
+        buildret = backend->buildVol(obj->conn, pool, buildvoldef, flags);
 
         storageDriverLock(driver);
         virStoragePoolObjLock(pool);
@@ -1473,7 +1473,7 @@ storageVolumeCreateXMLFrom(virStoragePoolPtr obj,
     virStorageVolPtr ret = NULL, volobj = NULL;
     int buildret;
 
-    virCheckFlags(0, NULL);
+    virCheckFlags(VIR_STORAGE_VOL_CREATE_PREALLOC_METADATA, NULL);
 
     storageDriverLock(driver);
     pool = virStoragePoolObjFindByUUID(&driver->pools, obj->uuid);