[PATCH] media-server: Add ability for retry.

[Christian Mauderer]

Hello Gedare,

thanks for the review.

On 17/07/2020 07:43, Gedare Bloom wrote:
> On Thu, Jul 9, 2020 at 2:21 AM Christian Mauderer
> <christian.mauderer at embedded-brains.de> wrote:
>>
>> This adds the possibility to request a retry in the media-listener if an
>> operation failed. Usefull for example if you want to automatically
>> reformat a disk if it wasn't possible to mount it.
>> ---
>>  cpukit/include/rtems/media.h |  3 +++
>>  cpukit/libblock/src/media.c  | 29 ++++++++++++++++-------------
>>  2 files changed, 19 insertions(+), 13 deletions(-)
>>
>> diff --git a/cpukit/include/rtems/media.h b/cpukit/include/rtems/media.h
>> index b2a3e2dc91..db13664975 100644
>> --- a/cpukit/include/rtems/media.h
>> +++ b/cpukit/include/rtems/media.h
>> @@ -281,6 +281,9 @@ typedef enum {
>>   *
>>   * @retval RTEMS_SUCCESSFUL Successful operation.
>>   * @retval RTEMS_IO_ERROR In the inquiry state this will abort the action.
>> + * @retval RTEMS_INCORRECT_STATE In the failed state this will cause a retry.
>> + * Make sure to have a retry counter or similar to avoid endless loops if you
>> + * use this this value.
> delete one 'this'
> 
> Glad you have this comment, that was my first thought when I read the
> commit msg.
> 
>>   */
>>  typedef rtems_status_code (*rtems_media_listener)(
>>    rtems_media_event event,
>> diff --git a/cpukit/libblock/src/media.c b/cpukit/libblock/src/media.c
>> index 5b2b06b5b2..c00825587c 100644
>> --- a/cpukit/libblock/src/media.c
>> +++ b/cpukit/libblock/src/media.c
>> @@ -420,26 +420,29 @@ static rtems_status_code process_event(
>>  )
>>  {
>>    rtems_status_code sc = RTEMS_SUCCESSFUL;
>> +  rtems_status_code sc_retry = RTEMS_SUCCESSFUL;
>>    rtems_media_state state = RTEMS_MEDIA_STATE_FAILED;
>>    char *dest = NULL;
>>
>> -  sc = notify(event, RTEMS_MEDIA_STATE_INQUIRY, src, NULL);
>> -  if (sc == RTEMS_SUCCESSFUL) {
>> -    state = RTEMS_MEDIA_STATE_READY;
>> -  } else {
>> -    state = RTEMS_MEDIA_STATE_ABORTED;
>> -  }
>> -
>> -  sc = (*worker)(state, src, &dest, worker_arg);
>> -  if (state == RTEMS_MEDIA_STATE_READY) {
>> +  do {
>> +    sc = notify(event, RTEMS_MEDIA_STATE_INQUIRY, src, NULL);
>>      if (sc == RTEMS_SUCCESSFUL) {
>> -      state = RTEMS_MEDIA_STATE_SUCCESS;
>> +      state = RTEMS_MEDIA_STATE_READY;
>>      } else {
>> -      state = RTEMS_MEDIA_STATE_FAILED;
>> +      state = RTEMS_MEDIA_STATE_ABORTED;
>> +    }
>> +
>> +    sc = (*worker)(state, src, &dest, worker_arg);
>> +    if (state == RTEMS_MEDIA_STATE_READY) {
>> +      if (sc == RTEMS_SUCCESSFUL) {
>> +        state = RTEMS_MEDIA_STATE_SUCCESS;
>> +      } else {
>> +        state = RTEMS_MEDIA_STATE_FAILED;
>> +      }
>>      }
>> -  }
>>
>> -  notify(event, state, src, dest);
>> +    sc_retry = notify(event, state, src, dest);
>> +  } while (state == RTEMS_MEDIA_STATE_FAILED && sc_retry == RTEMS_INCORRECT_STATE);
> line length
> 
> How do you use a retry counter? It's not obvious to me, but this is
> not an area I work with much.
> 

The retry is only done if explicitly requested by the media listener.
The media listener is a software provided by the user. If the user
requests a retry he should also decide how often he wants to retry the
operation.

A possibility to add a retry counter is to use the user specifiable
argument of the media listener. The user can provide a pointer to some
own data structure where the retries are counted.

I think the retries in general are a quite exotic feature. Like my
comment suggests I used it to try a mount for an on-board memory, if it
doesn't work I format the disk and retry the mount.

Best regards

Christian

>>    remember_event(event, state, src, dest);
>>
>>    if (state == RTEMS_MEDIA_STATE_SUCCESS) {
>> --
>> 2.26.2
>>
>> _______________________________________________
>> devel mailing list
>> devel at rtems.org
>> http://lists.rtems.org/mailman/listinfo/devel

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