Re: [PATCH V5 4/4] virtio-blk: Add REQ_FLUSH and REQ_FUA support to bio path

[Asias He <asias@redhat.com>]

On 08/06/2012 11:17 PM, Christoph Hellwig wrote:
> On Thu, Aug 02, 2012 at 02:43:04PM +0800, Asias He wrote:
>>> Even if it has a payload waiting is highly suboptimal and it should
>>> use a non-blocking sequencing like it is done in the request layer.
>>
>> So, for REQ_FLUSH, what we need is that send out the VIRTIO_BLK_T_FLUSH and
>> not to wait.
>
> If it's REQ_FLUSH without data a VIRTIO_BLK_T_FLUSH should be sent out only,
> if it's a REQ_FLUSH that has data a VIRTIO_BLK_T_FLUSH should be sent out,
> but instead of waiting for it to finish the I/O completion handler should
> then submit the actual write.
>
>> We still need to wait until the actual write is finished here?
>> Like,
>>
>> REQ_FUA is emulated by:
>> 1. Send the actual write
>> 2. Wait until the actual write is finished
>> 3. Send VIRTIO_BLK_T_FLUSH to device
>> 4. Signal the end of the write to upper layer
>
> Remove step 2 and run step 3 from the I/O completion handler.
>

Thanks for the explanation. V6 is in flight.

-- 
Asias