When sending SG_IO ioctls to a device: - /dev/sgX devices (using sg.c) follow the behavior described at http://tldp.org/HOWTO/SCSI-Generic-HOWTO/dio.html in terms of defaulting to indirect I/O, and using direct I/O only if both /proc/scsi/sg/allow_dio and SG_FLAG_DIRECT_IO in the request are set. - /dev/srX devices (using sr.c) default to direct I/O. At least, that appears to be the case from inspecting the code, as sr_block_ioctl->cdrom_ioctl->scsi_cmd_ioctl->sg_io->blk_rq_map_user->__blk_rq_map_user will attempt to map the pages, regardless of what the user specified in the request or in the proc node. This difference caught me by surprise; my expectation would be that an sg_io_hdr_t passed via SG_IO would be serviced in the same way regardless of the underlying driver. Is this a bug, or a feature? If the latter, is it documented somewhere? -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
