Re: [Qemu-devel] [PATCH v2 31/40] job: Add job_is_ready()

[John Snow <jsnow@redhat.com>]

On 05/18/2018 09:21 AM, Kevin Wolf wrote:
> Instead of having a 'bool ready' in BlockJob, add a function that
> derives its value from the job status.
> 
> At the same time, this fixes the behaviour to match what the QAPI
> documentation promises for query-block-job: 'true if the job may be
> completed'. When the ready flag was introduced in commit ef6dbf1e46e,
> the flag never had to be reset to match the description because after
> being ready, the jobs would immediately complete and disappear.
> 
> Job transactions and manual job finalisation were introduced only later.
> With these changes, jobs may stay around even after having completed
> (and they are not ready to be completed a second time), however their
> patches forgot to reset the ready flag.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> Reviewed-by: Max Reitz <mreitz@redhat.com>
> ---
>  include/block/blockjob.h |  5 -----
>  include/qemu/job.h       |  3 +++
>  blockjob.c               |  3 +--
>  job.c                    | 22 ++++++++++++++++++++++
>  qemu-img.c               |  2 +-
>  tests/test-blockjob.c    |  2 +-
>  6 files changed, 28 insertions(+), 9 deletions(-)
> 
> diff --git a/include/block/blockjob.h b/include/block/blockjob.h
> index 5a81afc6c3..8e1e1ee0de 100644
> --- a/include/block/blockjob.h
> +++ b/include/block/blockjob.h
> @@ -49,11 +49,6 @@ typedef struct BlockJob {
>      /** The block device on which the job is operating.  */
>      BlockBackend *blk;
>  
> -    /**
> -     * Set to true when the job is ready to be completed.
> -     */
> -    bool ready;
> -
>      /** Status that is published by the query-block-jobs QMP API */
>      BlockDeviceIoStatus iostatus;
>  
> diff --git a/include/qemu/job.h b/include/qemu/job.h
> index 1e8050c6fb..487f9d9a32 100644
> --- a/include/qemu/job.h
> +++ b/include/qemu/job.h
> @@ -367,6 +367,9 @@ bool job_is_cancelled(Job *job);
>  /** Returns whether the job is in a completed state. */
>  bool job_is_completed(Job *job);
>  
> +/** Returns whether the job is ready to be completed. */
> +bool job_is_ready(Job *job);
> +
>  /**
>   * Request @job to pause at the next pause point. Must be paired with
>   * job_resume(). If the job is supposed to be resumed by user action, call
> diff --git a/blockjob.c b/blockjob.c
> index 3ca009bea5..38f18e9ba3 100644
> --- a/blockjob.c
> +++ b/blockjob.c
> @@ -269,7 +269,7 @@ BlockJobInfo *block_job_query(BlockJob *job, Error **errp)
>      info->offset    = job->offset;
>      info->speed     = job->speed;
>      info->io_status = job->iostatus;
> -    info->ready     = job->ready;
> +    info->ready     = job_is_ready(&job->job),
>      info->status    = job->job.status;
>      info->auto_finalize = job->job.auto_finalize;
>      info->auto_dismiss  = job->job.auto_dismiss;
> @@ -436,7 +436,6 @@ void block_job_user_resume(Job *job)
>  void block_job_event_ready(BlockJob *job)
>  {
>      job_state_transition(&job->job, JOB_STATUS_READY);
> -    job->ready = true;
>  
>      if (block_job_is_internal(job)) {
>          return;
> diff --git a/job.c b/job.c
> index af31de4669..66ee26f2a0 100644
> --- a/job.c
> +++ b/job.c
> @@ -199,6 +199,28 @@ bool job_is_cancelled(Job *job)
>      return job->cancelled;
>  }
>  
> +bool job_is_ready(Job *job)
> +{
> +    switch (job->status) {
> +    case JOB_STATUS_UNDEFINED:
> +    case JOB_STATUS_CREATED:
> +    case JOB_STATUS_RUNNING:
> +    case JOB_STATUS_PAUSED:
> +    case JOB_STATUS_WAITING:
> +    case JOB_STATUS_PENDING:
> +    case JOB_STATUS_ABORTING:
> +    case JOB_STATUS_CONCLUDED:
> +    case JOB_STATUS_NULL:
> +        return false;
> +    case JOB_STATUS_READY:
> +    case JOB_STATUS_STANDBY:
> +        return true;
> +    default:
> +        g_assert_not_reached();
> +    }
> +    return false;
> +}
> +

What's the benefit to a switch statement with a default clause here,
over the shorter:

if (job->status == READY || job->status == STANDBY) {
  return true;
}
return false;

(Yes, I realize you already merged this code, but I'm still curious and
I need to read the series anyway to see what's changed...)

>  bool job_is_completed(Job *job)
>  {
>      switch (job->status) {
> diff --git a/qemu-img.c b/qemu-img.c
> index b2bcfc3df1..eecb7d3228 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -867,7 +867,7 @@ static void run_block_job(BlockJob *job, Error **errp)
>          aio_poll(aio_context, true);
>          qemu_progress_print(job->len ?
>                              ((float)job->offset / job->len * 100.f) : 0.0f, 0);
> -    } while (!job->ready && !job_is_completed(&job->job));
> +    } while (!job_is_ready(&job->job) && !job_is_completed(&job->job));
>  

Semantic change in this variable, but due to the way this function is
written it doesn't matter.

>      if (!job_is_completed(&job->job)) {
>          ret = job_complete_sync(&job->job, errp);
> diff --git a/tests/test-blockjob.c b/tests/test-blockjob.c
> index 7131cabb16..8180d03a5f 100644
> --- a/tests/test-blockjob.c
> +++ b/tests/test-blockjob.c
> @@ -185,7 +185,7 @@ static void coroutine_fn cancel_job_start(void *opaque)
>              goto defer;
>          }
>  
> -        if (!s->common.ready && s->should_converge) {
> +        if (!job_is_ready(&s->common.job) && s->should_converge) {
>              block_job_event_ready(&s->common);
>          }
>  
>