Re: [Qemu-devel] [PATCH V2 07/10] snapshot: qmp use new internal API for external snapshot transaction

[Wenchao Xia <xiawenc@linux.vnet.ibm.com>]

于 2013-3-13 18:18, Kevin Wolf 写道:
> Am 12.03.2013 um 09:30 hat Wenchao Xia geschrieben:
>>    I redesigned the structure, Following is the fake code:
>>
>> typedef struct BdrvActionOps {
>>      /* check the request's validation, allocate p_opaque if needed */
>>      int (*check)(BlockdevAction *action, void **p_opaque, Error **errp);
>>      /* take the action */
>>      int (*submit)(BlockdevAction *action, void *opaque, Error **errp);
>>      /* update emulator */
>>      int (*commit)(BlockdevAction *action, void *opaque, Error **errp);
>>      /* cancel the action */
>>      int (*rollback)(BlockdevAction *action, void *opaque, Error **errp);
>> } BdrvActionOps;
>
> Why do you need the split of prepare into check/submit?
>
> If you have prepare/commit/abort, everybody will recognise this as the
> standard transaction pattern because this is just how it's done.
> Deviating from it needs a good justification in my opinion.
>
> Kevin
>

   My thought is rejecting the request in *check if parameter invalid
before take any action, while submit do the real action, to reduce
the chance to of rolling back when some request not valid in the batch.

-- 
Best Regards

Wenchao Xia