block: Create proper size file for disk mirror

The qmp monitor command to mirror a disk was passing -1 for size
along with the disk's backing file. This size of the resulting disk
is the size of the backing file, which is incorrect if the disk
has been resized. Therefore we should always pass in the size of
the current disk.

Signed-off-by: Vishvananda Ishaya <vishvananda@gmail.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

blockdev.c

@@ -1282,11 +1282,11 @@ void qmp_drive_mirror(const char *device, const char *target,
         return;
     }
 
+    bdrv_get_geometry(bs, &size);
+    size *= 512;
     if (sync == MIRROR_SYNC_MODE_FULL && mode != NEW_IMAGE_MODE_EXISTING) {
         /* create new image w/o backing file */
         assert(format && drv);
-        bdrv_get_geometry(bs, &size);
-        size *= 512;
         bdrv_img_create(target, format,
                         NULL, NULL, NULL, size, flags, &local_err);
     } else {
@@ -1299,7 +1299,7 @@ void qmp_drive_mirror(const char *device, const char *target,
             bdrv_img_create(target, format,
                             source->filename,
                             source->drv->format_name,
-                            NULL, -1, flags, &local_err);
+                            NULL, size, flags, &local_err);
             break;
         default:
             abort();