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

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

30.07.2019 22:11, John Snow wrote:
> 
> 
> 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 <vsementsov@virtuozzo.com>
>> ---
>>
>> 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 ...?

What pairs do you mean?

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

Hmm, not simple for me to assume.. Is it a problem? And is it about this patch?

-- 
Best regards,
Vladimir