raw-format: Support BDRV_REQ_ZERO_WRITE for truncate

The raw format driver can simply forward the flag and let its bs->file
child take care of actually providing the zeros.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20200424125448.63318-6-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/raw-format.c

@@ -387,7 +387,7 @@ static int coroutine_fn raw_co_truncate(BlockDriverState *bs, int64_t offset,
 
     s->size = offset;
     offset += s->offset;
-    return bdrv_co_truncate(bs->file, offset, exact, prealloc, 0, errp);
+    return bdrv_co_truncate(bs->file, offset, exact, prealloc, flags, errp);
 }
 
 static void raw_eject(BlockDriverState *bs, bool eject_flag)
@@ -445,6 +445,8 @@ static int raw_open(BlockDriverState *bs, QDict *options, int flags,
     bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
         ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
             bs->file->bs->supported_zero_flags);
+    bs->supported_truncate_flags = bs->file->bs->supported_truncate_flags &
+                                   BDRV_REQ_ZERO_WRITE;
 
     if (bs->probed && !bdrv_is_read_only(bs)) {
         bdrv_refresh_filename(bs->file->bs);