[dm-devel] [PATCH 1/9] QUEUE_FLAG_NOWAIT to indicate device supports nowait

[Jens Axboe]

On 08/10/2017 11:15 AM, Goldwyn Rodrigues wrote:
> 
> 
> On 08/10/2017 09:14 AM, Jens Axboe wrote:
>> On 08/10/2017 05:38 AM, Goldwyn Rodrigues wrote:
>>>
>>>
>>> On 08/09/2017 09:18 PM, Jens Axboe wrote:
>>>> On 08/08/2017 02:36 PM, Jens Axboe wrote:
>>>>> On 08/08/2017 02:32 PM, Shaohua Li wrote:
>>>>>>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>>>>>>> index 25f6a0cb27d3..fae021ebec1b 100644
>>>>>>> --- a/include/linux/blkdev.h
>>>>>>> +++ b/include/linux/blkdev.h
>>>>>>> @@ -633,6 +633,7 @@ struct request_queue {
>>>>>>>  #define QUEUE_FLAG_REGISTERED  29	/* queue has been registered to a disk */
>>>>>>>  #define QUEUE_FLAG_SCSI_PASSTHROUGH 30	/* queue supports SCSI commands */
>>>>>>>  #define QUEUE_FLAG_QUIESCED    31	/* queue has been quiesced */
>>>>>>> +#define QUEUE_FLAG_NOWAIT      32	/* stack device driver supports REQ_NOWAIT */
>>>>>
>>>>> Does this work on 32-bit, where sizeof(unsigned long) == 32?
>>>>
>>>> I didn't get an answer to this one.
>>>>
>>>
>>> Oh, I assumed the question is rhetorical.
>>> No, it will not work on 32-bit. I was planning to change the field
>>> queue_flags to u64. Is that okay?
>>
>> No, besides that would not work with set/test_bit() and friends. Grab
>> a free bit instead.
>>
> 
> Which bit is free? I don't see any gaps in QUEUE_FLAG_*, and I am not
> sure if any one is unused.

Bit 0 is free in mainline, and I just looked, and two other bits are
gone as well:

http://git.kernel.dk/cgit/linux-block/commit/?h=for-4.14/block&id=e743eb1ecd5564b5ae0a4a76c1566f748a358839

-- 
Jens Axboe