Re: [Qemu-devel] [PATCH v3 4/9] block/commit: utilize job_exit shim

[Jeff Cody <jcody@redhat.com>]

On Wed, Aug 29, 2018 at 09:57:29PM -0400, John Snow wrote:
> Change the manual deferment to commit_complete into the implicit
> callback to job_exit, renaming commit_complete to commit_exit.
> 
> This conversion does change the timing of when job_completed is
> called to after the bdrv_replace_node and bdrv_unref calls, which
> could have implications for bjob->blk which will now be put down
> after this cleanup.
> 
> Kevin highlights that we did not take any permissions for that backend
> at job creation time, so it is safe to reorder these operations.
> 
> Signed-off-by: John Snow <jsnow@redhat.com>
> Reviewed-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/commit.c | 22 +++++-----------------
>  1 file changed, 5 insertions(+), 17 deletions(-)
> 
> diff --git a/block/commit.c b/block/commit.c
> index 4a17bb73ec..da69165de3 100644
> --- a/block/commit.c
> +++ b/block/commit.c
> @@ -68,19 +68,13 @@ static int coroutine_fn commit_populate(BlockBackend *bs, BlockBackend *base,
>      return 0;
>  }
>  
> -typedef struct {
> -    int ret;
> -} CommitCompleteData;
> -
> -static void commit_complete(Job *job, void *opaque)
> +static void commit_exit(Job *job)
>  {
>      CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
>      BlockJob *bjob = &s->common;
> -    CommitCompleteData *data = opaque;
>      BlockDriverState *top = blk_bs(s->top);
>      BlockDriverState *base = blk_bs(s->base);
>      BlockDriverState *commit_top_bs = s->commit_top_bs;
> -    int ret = data->ret;
>      bool remove_commit_top_bs = false;
>  
>      /* Make sure commit_top_bs and top stay around until bdrv_replace_node() */
> @@ -91,10 +85,10 @@ static void commit_complete(Job *job, void *opaque)
>       * the normal backing chain can be restored. */
>      blk_unref(s->base);
>  
> -    if (!job_is_cancelled(job) && ret == 0) {
> +    if (!job_is_cancelled(job) && job->ret == 0) {
>          /* success */
> -        ret = bdrv_drop_intermediate(s->commit_top_bs, base,
> -                                     s->backing_file_str);
> +        job->ret = bdrv_drop_intermediate(s->commit_top_bs, base,
> +                                          s->backing_file_str);
>      } else {
>          /* XXX Can (or should) we somehow keep 'consistent read' blocked even
>           * after the failed/cancelled commit job is gone? If we already wrote
> @@ -117,9 +111,6 @@ static void commit_complete(Job *job, void *opaque)
>       * bdrv_set_backing_hd() to fail. */
>      block_job_remove_all_bdrv(bjob);
>  
> -    job_completed(job, ret);
> -    g_free(data);
> -

Not having to allocate, track, and free this cumbersome return value for
each of these job specific completions now is pretty nice.

Reviewed-by: Jeff Cody <jcody@redhat.com>


>      /* If bdrv_drop_intermediate() didn't already do that, remove the commit
>       * filter driver from the backing chain. Do this as the final step so that
>       * the 'consistent read' permission can be granted.  */
> @@ -137,7 +128,6 @@ static void commit_complete(Job *job, void *opaque)
>  static int coroutine_fn commit_run(Job *job, Error **errp)
>  {
>      CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
> -    CommitCompleteData *data;
>      int64_t offset;
>      uint64_t delay_ns = 0;
>      int ret = 0;
> @@ -210,9 +200,6 @@ static int coroutine_fn commit_run(Job *job, Error **errp)
>  out:
>      qemu_vfree(buf);
>  
> -    data = g_malloc(sizeof(*data));
> -    data->ret = ret;
> -    job_defer_to_main_loop(&s->common.job, commit_complete, data);
>      return ret;
>  }
>  
> @@ -224,6 +211,7 @@ static const BlockJobDriver commit_job_driver = {
>          .user_resume   = block_job_user_resume,
>          .drain         = block_job_drain,
>          .run           = commit_run,
> +        .exit          = commit_exit,
>      },
>  };
>  
> -- 
> 2.14.4
>