On Tue, Feb 07, 2017 at 03:38:51PM +0100, Hannes Reinecke wrote: > The SCSI passthrough commands pass in pre-formatted SGLs, so the driver > just has to map them. > If we were converting that we first have to re-format the > (driver-specific) SGLs into linux sg lists, only to have them converted > back into driver-specific ones once queuecommand is called. > You sure it's worth the effort? > > The driver already reserves some tags for precisely this use-case, so it > won't conflict with normal I/O operation. > So where's the problem with that?
If it was an entirely separate path that would be easy, but it's not - see all the poking into the tag maps that your patch 8 includes. If it was just a few tags on the side not interacting with the scsi or blk-mq it wouldn't be such a problem.
