On 06/01/2017 12:17 PM, Bart Van Assche wrote:
> On Thu, 2017-06-01 at 12:06 -0700, Jens Axboe wrote:
>> On 06/01/2017 06:11 AM, Bart Van Assche wrote:
>>> On Thu, 2017-06-01 at 08:08 +0200, Christoph Hellwig wrote:
>>>> On Wed, May 31, 2017 at 03:52:46PM -0700, Bart Van Assche wrote:
>>>>> Commit 6d247d7f71d1 ("block: allow specifying size for extra command
>>>>> data") added support for .cmd_size to blk-sq. Due to that patch the
>>>>> blk_mq_rq_{to,from}_pdu() functions are also useful for single-queue
>>>>> block drivers. Hence remove "_mq" from the name of these functions.
>>>>> This patch does not change any functionality. Most of this patch has
>>>>> been generated by running the following shell command:
>>>>
>>>> I don't really see the point of this as it's primarily a blk-mq API
>>>> and we still hope to get rid of the old code. But I'm not necessarily
>>>> against it either.
>>>
>>> I would like to introduce calls to these functions in several scsi-sq
>>> functions. If I would do that without renaming these functions then anyone
>>> who reads the code of these functions and sees calls to functions with a
>>> blk_mq_ prefix could get really confused when trying to figure out whether
>>> these functions are used by scsi-sq, scsi-mq or perhaps both.
>>
>> But that should go away, eventually.
>
> Hello Jens,
>
> I agree that we should work towards removal of the single queue block layer.
> But how long will it take before that code is removed?
>
> Due to recent patches from Christoph the 'request' member in struct scsi_cmnd
> is now superfluous. I'd like to replace accesses to that member by a call to
> blk_mq_rq_from_pdu(). I'm afraid that doing that in scsi-sq code paths will
> make that code look weird.
For the old path, I'd suggest that you just wrap the blk_mq_*_pdu() calls
with a non-mq named version, and stuff that in blkdev.h. That way we can
keep the blk-mq API more logical, and we can just kill those wrappers
when the last user goes away.
That's also a lot less churn than renaming all of the existing callers.
--
Jens Axboe
