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Date: Thu, 3 Nov 2016 14:17:34 +0100
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3 5/6] blockjob: refactor backup_start as
 backup_job_create
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To: John Snow <jsnow@redhat.com>
Cc: qemu-block@nongnu.org, vsementsov@virtuozzo.com, stefanha@redhat.com, pbonzini@redhat.com, jcody@redhat.com, qemu-devel@nongnu.org

Am 02.11.2016 um 18:50 hat John Snow geschrieben:
> Refactor backup_start as backup_job_create, which only creates the job,
> but does not automatically start it. The old interface, 'backup_start',
> is not kept in favor of limiting the number of nearly-identical interfaces
> that would have to be edited to keep up with QAPI changes in the future.
> 
> Callers that wish to synchronously start the backup_block_job can
> instead just call block_job_start immediately after calling
> backup_job_create.
> 
> Transactions are updated to use the new interface, calling block_job_start
> only during the .commit phase, which helps prevent race conditions where
> jobs may finish before we even finish building the transaction. This may
> happen, for instance, during empty block backup jobs.
> 
> Reported-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> Signed-off-by: John Snow <jsnow@redhat.com>

> +static void drive_backup_commit(BlkActionState *common)
> +{
> +    DriveBackupState *state = DO_UPCAST(DriveBackupState, common, common);
> +    if (state->job) {
> +        block_job_start(state->job);
> +    }
>  }

How could state->job ever be NULL?

Same question for abort, and for blockdev_backup_commit/abort.

Kevin