[sheepdog] [PATCH] sheep: no need to set SD_FLAG_CMD_WRITE for local request

[Liu Yuan]

On 08/28/2012 05:41 PM, MORITA Kazutaka wrote:
> At Tue, 28 Aug 2012 16:43:50 +0800,
> levin li wrote:
>>
>> On 08/28/2012 04:38 PM, Liu Yuan wrote:
>>> On 08/28/2012 04:14 PM, levin li wrote:
>>>> -	hdr.flags = SD_FLAG_CMD_WRITE;
>>>>  	hdr.data_length = sizeof(sys->this_node);
>>>
>>> Why not? We do write &sys->this_node as data to transfer.
>>>
>>> Thanks,
>>> Yuan
>>>
>>
>> For cluster requests we send data through cluster driver (corosync or zookeeper),
>> in which case SD_FLAG_CMD_WRITE is never used.
> 
> This change looks really strange to me.  If SD_FLAG_CMD_WRITE is set,
> hdr.data_length means the size of the sent data, and if not, it means
> the size of receive data buffer.
> 
> I think we shouldn't do multicast the data when SD_FLAG_CMD_WRITE is
> not set.
> 

This is twofold. Strictly checking sometimes cause trouble for
programmers, at least for me, I had several gloomy times debugging when
I forgot to assign SD_FLAG_CMD_WRITE. It is easy to forget especially we
set opcode with WRITE. Even for now, I am considering if we can remove
this flag, because we might get data direction from opcode.

So IIUC, SD_FLAG_CMD_WRITE is used for header handling, indicating if
there is any data to read from the payload. For local request, we don't
need data transfer at all, the request is made up locally.

Thanks,
Yuan