The default value of x-check-cache-dropped is false. There's no reason
to use the previous value as a default in raw_reopen_prepare() because
bdrv_reopen_queue_child() already takes care of putting the old
options in the BDRVReopenState.options QDict.

If x-check-cache-dropped was previously set but is now missing from
the reopen QDict then it should be reset to false.

Signed-off-by: Alberto Garcia <berto@igalia.com>
---
 block/file-posix.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index fe83cbf0eb..ddac0cc3e6 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -851,7 +851,7 @@ static int raw_reopen_prepare(BDRVReopenState *state,
     }
 
     rs->check_cache_dropped = qemu_opt_get_bool(opts, "x-check-cache-dropped",
-                                                s->check_cache_dropped);
+                                                false);
 
     if (s->type == FTYPE_CD) {
         rs->open_flags |= O_NONBLOCK;
-- 
2.11.0

On 2018-08-26 16:09, Alberto Garcia wrote:
> The default value of x-check-cache-dropped is false. There's no reason
> to use the previous value as a default in raw_reopen_prepare() because
> bdrv_reopen_queue_child() already takes care of putting the old
> options in the BDRVReopenState.options QDict.

Well, the reason would be because one might want to retain unspecified
values as they were set before.  But we decided we don't want to do that.

> If x-check-cache-dropped was previously set but is now missing from
> the reopen QDict then it should be reset to false.
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
>  block/file-posix.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

So:

Reviewed-by: Max Reitz <mreitz@redhat.com>