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

[John Snow <jsnow@redhat.com>]

On 7/31/19 6:28 AM, Vladimir Sementsov-Ogievskiy wrote:
> 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?

blk_ref / blk_unref in the backup and mirror specific drain paths.

> 
>>
>> 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?
>