Each block queue has a ->dma_alignment field, which is set to 511 by default unless changed. Everything not aligned to that will be bounced in __blk_rq_map_user_iov and friends before we send it to the driver.
Thanks, I missed the default setting...
I also just tested Bart's unaligned test [1] on scsi_debug and it seems to go through as well (alignment and length are 4)...SCSI reduces the alignment in __scsi_init_queue: /* * set a reasonable default alignment on word boundaries: the * host and device may alter it using * blk_queue_update_dma_alignment() later. */ blk_queue_dma_alignment(q, 0x03);
That explains why I was able to test that with iSER :) I guess I didn't test single byte alignment after all, but I definitely remember using less than a sector...
still would fit NVMe dword-alignment SGLs, though :)
I would say its useful to have, but its only relevant to ioctls as normal io we explicitly on sub logical block size alignment. Anyways, I still think having ctrl->virt_boundary instead of ctrl->sg_gap_support is cleaner... -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
