On 07/05/2017 05:08 PM, Eric Blake wrote:
> stream_complete() skips the work of rewriting the backing file if
> the job was cancelled, if data->reached_end is false, or if there
> was an error detected (non-zero data->ret) during the streaming.
> But note that in stream_run(), data->reached_end is only set if the
> loop ran to completion, and data->ret is only 0 in two cases:
> either the loop ran to completion (possibly by cancellation, but
> stream_complete checks for that), or we took an early goto out
> because there is no bs->backing. Thus, we can preserve the same
> semantics without the use of reached_end, by merely checking for
> bs->backing (and logically, if there was no backing file, streaming
> is a no-op, so there is no backing file to rewrite).
>
> Suggested-by: Kevin Wolf <kwolf@redhat.com>
> Signed-off-by: Eric Blake <eblake@redhat.com>
>
> ---
> v4: new patch
> ---
> block/stream.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/block/stream.c b/block/stream.c
> index 746d525..12f1659 100644
> --- a/block/stream.c
> +++ b/block/stream.c
> @@ -59,7 +59,6 @@ static int coroutine_fn stream_populate(BlockBackend *blk,
>
> typedef struct {
> int ret;
> - bool reached_end;
> } StreamCompleteData;
>
> static void stream_complete(BlockJob *job, void *opaque)
> @@ -70,7 +69,7 @@ static void stream_complete(BlockJob *job, void *opaque)
> BlockDriverState *base = s->base;
> Error *local_err = NULL;
>
> - if (!block_job_is_cancelled(&s->common) && data->reached_end &&
> + if (!block_job_is_cancelled(&s->common) && bs->backing &&
> data->ret == 0) {
> const char *base_id = NULL, *base_fmt = NULL;
> if (base) {
> @@ -211,7 +210,6 @@ out:
> /* Modify backing chain and close BDSes in main loop */
> data = g_malloc(sizeof(*data));
> data->ret = ret;
> - data->reached_end = sector_num == end;
> block_job_defer_to_main_loop(&s->common, stream_complete, data);
> }
>
This seems ever so slightly less intuitive to me, but it is functionally
identical.
Reviewed-by: John Snow <jsnow@redhat.com>