parallels: drop check that bdrv_truncate() is working

This would be actually strange and error prone. If truncate() nowadays
will fail, there is something fatally wrong. Let's check for that during
the actual work.

The only fallback case is when the file is not zero initialized. In this
case we should switch to preallocation via fallocate().

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Markus Armbruster <armbru@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Max Reitz <mreitz@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block/parallels.c b/block/parallels.c
index 6794e53..e1e06d2 100644
--- a/block/parallels.c
+++ b/block/parallels.c
@@ -703,9 +703,7 @@
         goto fail_options;
     }
 
-    if (!(flags & BDRV_O_RESIZE) || !bdrv_has_zero_init(bs->file->bs) ||
-            bdrv_truncate(bs->file, bdrv_getlength(bs->file->bs),
-                          PREALLOC_MODE_OFF, NULL) != 0) {
+    if (!bdrv_has_zero_init(bs->file->bs)) {
         s->prealloc_mode = PRL_PREALLOC_MODE_FALLOCATE;
     }