SMR (Shingled Magnetic Recording) disk drives are able to achieve higher areal density, at the cost of making media write operations to the disk more inflexible (i.e., divides the disk into multiple zones, each of which can be written sequentially only). Following on some discussions in the Linux filesystem community around SMR [1][2], I'd like to work on adding early support for SMR-related SCSI commands (ZBC, or Zoned Block Commands [3]). First, I'd like to ask the Linux SCSI/ filesystem communities for advice and recommendations on how to go about it. [1] http://thread.gmane.org/gmane.linux.file-systems/81970/focus=82309 [2] http://www.spinics.net/lists/linux-fsdevel/msg72305.html [3] http://www.t10.org/cgi-bin/ac.pl?t=d&f=14-010r8.pdf I'm thinking of classifying an SMR disk drive as an sd-type SCSI device, as SMR is expected to be delivered in the form of an add-on/enhancement to existing traditional disk drives. SMR disk drives will continue to support random read capability. As for exposing ZBC to upper layers of the stack, I'm thinking of two potential ways: A) As an ioctl handled by sd_ioctl(), in drivers/scsi/sd.c B) As a request command flag type handled by sd_prep_fn(), in drivers/scsi/sd.c For A), sd_ioctl() in drivers/scsi/sd.c may look something like: (not a patch) static int sd_ioctl(struct block_device *bdev, fmode_t mode, unsigned int cmd, unsigned long arg) { ... (abridged) ... /* * Send SCSI addressing ioctls directly to mid level, send other * ioctls to block level and then onto mid level if they can't be * resolved. */ switch (cmd) { + case SD_REPORT_ZONES: + case SD_RESET_WRITEPNTR: + error = sd_smr_command(sdp, cmd, p); + break; case SCSI_IOCTL_GET_IDLUN: case SCSI_IOCTL_GET_BUS_NUMBER: error = scsi_ioctl(sdp, cmd, p); break; default: error = scsi_cmd_blk_ioctl(bdev, mode, cmd, p); if (error != -ENOTTY) break; error = scsi_ioctl(sdp, cmd, p); break; } out: return error; } For B), sd_prep_fn() in drivers/scsi/sd.c may look something like: (not a patch) static int sd_prep_fn(struct request_queue *q, struct request *rq) { struct scsi_cmnd *SCpnt; struct scsi_device *sdp = q->queuedata; struct gendisk *disk = rq->rq_disk; struct scsi_disk *sdkp; sector_t block = blk_rq_pos(rq); sector_t threshold; unsigned int this_count = blk_rq_sectors(rq); int ret, host_dif; unsigned char protect; /* * Discard request come in as REQ_TYPE_FS but we turn them into * block PC requests to make life easier. */ if (rq->cmd_flags & REQ_DISCARD) { ret = sd_setup_discard_cmnd(sdp, rq); goto out; + } else if (rq->cmd_flags & REQ_REPORT_ZONES) { + ret = sd_setup_report_zones_cmnd(sdp, rq); + goto out; + } else if (rq->cmd_flags & REQ_RESET_WRITEPNTR) { + ret = sd_setup_reset_writepntr_cmnd(sdp, rq); + goto out; } else if (rq->cmd_flags & REQ_WRITE_SAME) { ret = sd_setup_write_same_cmnd(sdp, rq); goto out; } else if (rq->cmd_flags & REQ_FLUSH) { ret = scsi_setup_flush_cmnd(sdp, rq); goto out; } else if (rq->cmd_type == REQ_TYPE_BLOCK_PC) { ret = scsi_setup_blk_pc_cmnd(sdp, rq); goto out; } else if (rq->cmd_type != REQ_TYPE_FS) { ret = BLKPREP_KILL; goto out; } ret = scsi_setup_fs_cmnd(sdp, rq); if (ret != BLKPREP_OK) goto out; SCpnt = rq->special; sdkp = scsi_disk(disk); ... (abridged) ... } I'd very much appreciate feedback/comments on the directions above. Thanks. Han -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
