Re: [Qemu-devel] [PATCH v3] blockjob: drain all job nodes in block_job_drain

[John Snow]

On 7/24/19 5:40 AM, Vladimir Sementsov-Ogievskiy wrote:
> Instead of draining additional nodes in each job code, let's do it in
> common block_job_drain, draining just all job's children.
> BlockJobDriver.drain becomes unused, so, drop it at all.
> 
> It's also a first step to finally get rid of blockjob->blk.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> ---
> 
> v3: just resend, as I've some auto returned mails and not sure that
>     v2 reached recipients.
> 
> v2: apply Max's suggestions:
>  - drop BlockJobDriver.drain
>  - do firtly loop of bdrv_drained_begin and then separate loop
>    of bdrv_drained_end.
> 
>    Hmm, a question here: should I call bdrv_drained_end in reverse
>    order? Or it's OK as is?
> 

I think it should be OK. These nodes don't necessarily have a well
defined relationship between each other, do they?

>  include/block/blockjob_int.h | 11 -----------
>  block/backup.c               | 18 +-----------------
>  block/mirror.c               | 26 +++-----------------------
>  blockjob.c                   | 13 ++++++++-----
>  4 files changed, 12 insertions(+), 56 deletions(-)
> 

Nice diffstat :)

> diff --git a/include/block/blockjob_int.h b/include/block/blockjob_int.h
> index e4a318dd15..e1abf4ee85 100644
> --- a/include/block/blockjob_int.h
> +++ b/include/block/blockjob_int.h
> @@ -52,17 +52,6 @@ struct BlockJobDriver {
>       * besides job->blk to the new AioContext.
>       */
>      void (*attached_aio_context)(BlockJob *job, AioContext *new_context);
> -
> -    /*
> -     * If the callback is not NULL, it will be invoked when the job has to be
> -     * synchronously cancelled or completed; it should drain 
> BlockDriverStates
> -     * as required to ensure progress.
> -     *
> -     * Block jobs must use the default implementation for job_driver.drain,
> -     * which will in turn call this callback after doing generic block job
> -     * stuff.
> -     */
> -    void (*drain)(BlockJob *job);

I was about to say "huh?" ... but then realized you're deleting this
confusing glob. Good.

>  };
>  
>  /**
> diff --git a/block/backup.c b/block/backup.c
> index 715e1d3be8..7930004bbd 100644
> --- a/block/backup.c
> +++ b/block/backup.c
> @@ -320,21 +320,6 @@ void backup_do_checkpoint(BlockJob *job, Error **errp)
>      hbitmap_set(backup_job->copy_bitmap, 0, backup_job->len);
>  }
>  
> -static void backup_drain(BlockJob *job)
> -{
> -    BackupBlockJob *s = container_of(job, BackupBlockJob, common);
> -
> -    /* Need to keep a reference in case blk_drain triggers execution
> -     * of backup_complete...
> -     */
> -    if (s->target) {
> -        BlockBackend *target = s->target;
> -        blk_ref(target);
> -        blk_drain(target);
> -        blk_unref(target);
> -    }
> -}
> -

Adios ...

>  static BlockErrorAction backup_error_action(BackupBlockJob *job,
>                                              bool read, int error)
>  {
> @@ -493,8 +478,7 @@ static const BlockJobDriver backup_job_driver = {
>          .commit                 = backup_commit,
>          .abort                  = backup_abort,
>          .clean                  = backup_clean,
> -    },
> -    .drain                  = backup_drain,
> +    }
>  };
>  

This pleases the eyes.

>  static int64_t backup_calculate_cluster_size(BlockDriverState *target,
> diff --git a/block/mirror.c b/block/mirror.c
> index 8cb75fb409..8456ccd89d 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -644,14 +644,11 @@ static int mirror_exit_common(Job *job)
>      bdrv_ref(mirror_top_bs);
>      bdrv_ref(target_bs);
>  
> -    /* Remove target parent that still uses BLK_PERM_WRITE/RESIZE before
> +    /*
> +     * Remove target parent that still uses BLK_PERM_WRITE/RESIZE before

(Thanks, patchew...)

>       * inserting target_bs at s->to_replace, where we might not be able to 
> get
>       * these permissions.
> -     *
> -     * Note that blk_unref() alone doesn't necessarily drop permissions 
> because
> -     * we might be running nested inside mirror_drain(), which takes an extra
> -     * reference, so use an explicit blk_set_perm() first. */
> -    blk_set_perm(s->target, 0, BLK_PERM_ALL, &error_abort);
> +     */
>      blk_unref(s->target);
>      s->target = NULL;
>  
> @@ -1143,21 +1140,6 @@ static bool mirror_drained_poll(BlockJob *job)
>      return !!s->in_flight;
>  }
>  
> -static void mirror_drain(BlockJob *job)
> -{
> -    MirrorBlockJob *s = container_of(job, MirrorBlockJob, common);
> -
> -    /* Need to keep a reference in case blk_drain triggers execution
> -     * of mirror_complete...
> -     */
> -    if (s->target) {
> -        BlockBackend *target = s->target;
> -        blk_ref(target);
> -        blk_drain(target);
> -        blk_unref(target);
> -    }
> -}
> -
>  static const BlockJobDriver mirror_job_driver = {
>      .job_driver = {
>          .instance_size          = sizeof(MirrorBlockJob),
> @@ -1172,7 +1154,6 @@ static const BlockJobDriver mirror_job_driver = {
>          .complete               = mirror_complete,
>      },
>      .drained_poll           = mirror_drained_poll,
> -    .drain                  = mirror_drain,
>  };
>  
>  static const BlockJobDriver commit_active_job_driver = {
> @@ -1189,7 +1170,6 @@ static const BlockJobDriver commit_active_job_driver = {
>          .complete               = mirror_complete,
>      },
>      .drained_poll           = mirror_drained_poll,
> -    .drain                  = mirror_drain,
>  };
>  
>  static void coroutine_fn
> diff --git a/blockjob.c b/blockjob.c
> index 20b7f557da..78cf71d6c8 100644
> --- a/blockjob.c
> +++ b/blockjob.c
> @@ -92,12 +92,15 @@ void block_job_free(Job *job)
>  void block_job_drain(Job *job)
>  {
>      BlockJob *bjob = container_of(job, BlockJob, job);
> -    const JobDriver *drv = job->driver;
> -    BlockJobDriver *bjdrv = container_of(drv, BlockJobDriver, job_driver);
> +    GSList *l;
>  
> -    blk_drain(bjob->blk);
> -    if (bjdrv->drain) {
> -        bjdrv->drain(bjob);
> +    for (l = bjob->nodes; l; l = l->next) {
> +        BdrvChild *c = l->data;
> +        bdrv_drained_begin(c->bs);
> +    }
> +    for (l = bjob->nodes; l; l = l->next) {
> +        BdrvChild *c = l->data;
> +        bdrv_drained_end(c->bs);
>      }
>  }
>  
> 

Seems much nicer to me. What becomes of the ref/unref pairs?

I guess not needed anymore?, since job cleanup necessarily happens in
the main loop context now and we don't have a backup_complete function
anymore ...?

In the cases where auto_finalize=true, do we have any guarantee that the
completion callbacks cannot be scheduled while we are here?