Christoph, >> 1. We are using RQF_SPECIAL_PAYLOAD for only discard commands and not >> for write-zeroes because it does not have any payload. Using this in >> the code will trigger more code changes to handle in the completion >> path. > > Yes. And that is the big difference to SCSI where REQ_OP_WRITE_ZEROES > turns into a WRITE SAME command that has a payload. So for SCSI > RQF_SPECIAL_PAYLOAD for REQ_OP_WRITE_ZEROES makes a lot of sense, for > NVMe it does not. I don't actually care about using RQF_SPECIAL, it just seemed like a quick workaround to set it and make bv_len 0. My concern is purely rooted in all the grief we've had throughout the block I/O stack distinguishing between the bytes acted upon on media and the DMA transfer length. And consequently, I don't particularly like that blk_rq_payload_bytes() doesn't handle the NVMe WRITE ZEROES command. That seems like something that will cause us headaches in the future... -- Martin K. Petersen Oracle Linux Engineering
