Re: [RFC PATCH v2 02/14] job.h: categorize fields in struct Job

[Emanuele Giuseppe Esposito <eesposit@redhat.com>]

On 16/12/2021 17:21, Stefan Hajnoczi wrote:
> On Thu, Nov 04, 2021 at 10:53:22AM -0400, Emanuele Giuseppe Esposito wrote:
>> Categorize the fields in struct Job to understand which ones
>> need to be protected by the job mutex and which don't.
>>
>> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
>> ---
>>   include/qemu/job.h | 57 +++++++++++++++++++++++++++-------------------
>>   1 file changed, 34 insertions(+), 23 deletions(-)
>>
>> diff --git a/include/qemu/job.h b/include/qemu/job.h
>> index ccf7826426..f7036ac6b3 100644
>> --- a/include/qemu/job.h
>> +++ b/include/qemu/job.h
>> @@ -40,27 +40,52 @@ typedef struct JobTxn JobTxn;
>>    * Long-running operation.
>>    */
>>   typedef struct Job {
>> +
>> +    /* Fields set at initialization (job_create), and never modified */
>> +
>>       /** The ID of the job. May be NULL for internal jobs. */
>>       char *id;
>>   
>> -    /** The type of this job. */
>> +    /**
>> +     * The type of this job.
>> +     * All callbacks are called with job_mutex *not* held.
>> +     */
>>       const JobDriver *driver;
>>   
>> -    /** Reference count of the block job */
>> -    int refcnt;
>> -
>> -    /** Current state; See @JobStatus for details. */
>> -    JobStatus status;
>> -
>>       /** AioContext to run the job coroutine in */
>>       AioContext *aio_context;
> 
> "Fields set at initialization (job_create), and never modified" does not
> apply here. blockjob.c:child_job_set_aio_ctx() changes it at runtime.
> 

Right. aio_context can theoretically avoid also the job_mutex, if we 
make sure that all klass->set_aio_ctx() are under BQL (they are) and 
under drains (work in progress). For now I will protect it with job_lock().

Thank you,
Emanuele