On 01/27/2017 10:27 PM, Bart Van Assche wrote: > On Wed, 2017-01-25 at 18:25 +0100, Christoph Hellwig wrote: >> 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. >> >> Changes since V1: >> - fix handling of a NULL sense pointer in __scsi_execute >> - clean up handling of the flush flags in the block layer and MD >> - additional small cleanup in dm-rq > > Hello Christoph, > > A general comment: patch "block: allow specifying size for extra > command data" is a very welcome improvement but unfortunately also > introduces an inconsistency among block drivers. This patch series > namely creates two kinds of block drivers: > - Block drivers that use the block layer core to allocate > request-private data. These block drivers set request.cmd_size > to a non-zero value and do not need request.special. > - Block drivers that allocate request-private data themselves. > These block drivers set request.cmd_size to zero and use > request.special to translate a request pointer into the private > data pointer. > > Have you considered to convert all block drivers to the new > approach and to get rid of request.special? If so, do you already > have plans to start working on this? I'm namely wondering wheter I > should start working on this myself. > I was actually looking into it, too. Once scsi passthrough is removed from struct request there is no reasonable need to rely on '->special' for anything, and we should just ditch it. Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare@xxxxxxx +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG Nürnberg) -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
