Re: [PATCH 1/2] scsi_host: add support for request batching

Paolo Bonzini
2019-07-04T13:19:13Z

On 19/06/19 12:31, Paolo Bonzini wrote:
>> I'm a bit unsure if 'bd->last' is always set; it's quite obvious that
>> it's present if set, but what about requests with 'bd->last == false' ?
>> Is there a guarantee that they will _always_ be followed with a request
>> with bd->last == true?
>> And if so, is there a guarantee that this request is part of the same batch?
> It's complicated. A request with bd->last == false _will_ always be
> followed by a request with bd->last == true in the same batch. However,
> due to e.g. errors it may be possible that the last request is not sent.
> In that case, the block layer sends commit_rqs, as documented in the
> comment above, to flush the requests that have been sent already.
>
> So, a driver that obeys bd->last (or SCMD_LAST) but does not implement
> commit_rqs is bound to have bugs, which is why this patch was not split
> further.
>
> Makes sense?

Hannes, can you provide your Reviewed-by?

Thanks,

Paolo