[dm-devel] [PATCH 01/11] blk-mq: Add blk_mq_init_queue_ops()

[John Garry]

On 22/03/2022 11:18, Christoph Hellwig wrote:
> On Tue, Mar 22, 2022 at 06:39:35PM +0800, John Garry wrote:
>> Add an API to allocate a request queue which accepts a custom set of
>> blk_mq_ops for that request queue.
>>
>> The reason which we may want custom ops is for queuing requests which we
>> don't want to go through the normal queuing path.
> 
> Eww.  I really do not think we should do separate ops per queue, as that
> is going to get us into a deep mess eventually.
> 

Yeah... so far (here) it works out quite nicely, as we don't need to 
change the SCSI blk mq ops nor allocate a scsi_device - everything is 
just separate.

The other method mentioned previously was to add the request "reserved" 
flag and add new paths in scsi_queue_rq() et al to handle this, but that 
gets messy.

Any other ideas ...?

Cheers,
John