On Tue, Jan 10 2017 at 10:06am -0500, Christoph Hellwig <hch@xxxxxx> wrote: > Hi all, > > this series splits the support for SCSI passthrough commands from the > main struct request used all over the block layer into a separate > scsi_request structure that drivers that want to support SCSI passthough > need to embedded as the first thing into their request-private data, > similar to how we handle NVMe passthrough commands. > > To support this I've added support for that the private data after > request structure to the legacy request path instead, so that it can > be treated the same way as the blk-mq path. Compare to the current > scsi_cmnd allocator that actually is a major simplification. > > There is one major show-stopper for the series as-is: Request-based > device mapper currently allocate the request structures in the stacking > driver without a knowledge of the queue it's going to be submitte on > for the legacy request path. It managed to avoid that issue for the > blk-mq path, but that currently can't be used on legacy request devices > for reasons I don't fully understand. We'll need to figure out how > sort this out, but maybe that's a good opportunity to drop one or two > of the three different dm-mpath I/O paths? :) Ah, should've read the 0th patch earlier.. I removed blk-mq on request_fn paths support because it was one of the permutations that I felt least useful/stable (see commit c5248f79f3 "dm: remove support for stacking dm-mq on .request_fn device(s)") As for all of the different IO paths. I've always liked the idea of blk-mq ruling the world. With Jens' blk-mq IO scheduling advances maybe we're closer! -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
