Re: [PATCH v9 2/2] ublk: enable zoned storage support

[Ming Lei]

On Fri, Jul 14, 2023 at 09:25:10AM +0200, Andreas Hindborg wrote:
> From: Andreas Hindborg <a.hindborg@xxxxxxxxxxx>
> 
> Add zoned storage support to ublk: report_zones and operations:
>  - REQ_OP_ZONE_OPEN
>  - REQ_OP_ZONE_CLOSE
>  - REQ_OP_ZONE_FINISH
>  - REQ_OP_ZONE_RESET
>  - REQ_OP_ZONE_APPEND
> 
> The zone append feature uses the `addr` field of `struct ublksrv_io_cmd` to
> communicate ALBA back to the kernel. Therefore ublk must be used with the
> user copy feature (UBLK_F_USER_COPY) for zoned storage support to be
> available. Without this feature, ublk will not allow zoned storage support.
> 
> Signed-off-by: Andreas Hindborg <a.hindborg@xxxxxxxxxxx>
> ---

...

> +/*
> + * Construct a zone report. The report request is carried in `struct
> + * ublksrv_io_desc`. The `start_sector` field must be the first sector of a zone
> + * and shall indicate the first zone of the report. The `nr_sectors` shall
> + * indicate how many zones should be reported (divide by zone size to get number
> + * of zones in the report) and must be an integer multiple of the zone size. The
> + * report shall be delivered as a `struct blk_zone` array. To report fewer zones
> + * than requested, zero the last entry of the returned array.
> + */
> +#define		UBLK_IO_OP_REPORT_ZONES		18

Actually, I meant the following delta change in V8 comment, then the UAPI
looks more clean & readable wrt. reporting how many zones in UBLK_IO_OP_REPORT_ZONES
and reusing ublksrv_io_cmd->addr.

Otherwise, this patchset looks fine.


diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 5698f4575e05..454c852ed328 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -70,7 +70,7 @@ struct ublk_rq_data {
 	struct kref ref;
 	__u64 sector;
 	__u32 operation;
-	__u32 nr_sectors;
+	__u32 nr_zones;
 };
 
 struct ublk_uring_cmd_pdu {
@@ -335,7 +335,7 @@ static int ublk_report_zones(struct gendisk *disk, sector_t sector,
 		pdu = blk_mq_rq_to_pdu(req);
 		pdu->operation = UBLK_IO_OP_REPORT_ZONES;
 		pdu->sector = sector;
-		pdu->nr_sectors = zones_in_request * zone_size_sectors;
+		pdu->nr_zones = zones_in_request;
 
 		ret = blk_rq_map_kern(disk->queue, req, buffer, buffer_length,
 					GFP_KERNEL);
@@ -404,7 +404,7 @@ static blk_status_t ublk_setup_iod_zoned(struct ublk_queue *ubq,
 		switch (ublk_op) {
 		case UBLK_IO_OP_REPORT_ZONES:
 			iod->op_flags = ublk_op | ublk_req_build_flags(req);
-			iod->nr_sectors = pdu->nr_sectors;
+			iod->nr_zones = pdu->nr_zones;
 			iod->start_sector = pdu->sector;
 			return BLK_STS_OK;
 		default:
diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
index 4d97eb0f7d13..602a788a650e 100644
--- a/include/uapi/linux/ublk_cmd.h
+++ b/include/uapi/linux/ublk_cmd.h
@@ -249,11 +249,13 @@ struct ublksrv_ctrl_dev_info {
 /*
  * Construct a zone report. The report request is carried in `struct
  * ublksrv_io_desc`. The `start_sector` field must be the first sector of a zone
- * and shall indicate the first zone of the report. The `nr_sectors` shall
- * indicate how many zones should be reported (divide by zone size to get number
- * of zones in the report) and must be an integer multiple of the zone size. The
- * report shall be delivered as a `struct blk_zone` array. To report fewer zones
- * than requested, zero the last entry of the returned array.
+ * and shall indicate the first zone of the report. The `nr_zones` shall
+ * indicate how many zones should be reported at most. The report shall be
+ * delivered as a `struct blk_zone` array. To report fewer zones than
+ * requested, zero the last entry of the returned array.
+ *
+ * So related definitions(blk_zone, blk_zone_cond, blk_zone_type, ...) in
+ * include/uapi/linux/blkzoned.h are part of ublk UAPI.
  */
 #define		UBLK_IO_OP_REPORT_ZONES		18
 
@@ -276,7 +278,10 @@ struct ublksrv_io_desc {
 	/* op: bit 0-7, flags: bit 8-31 */
 	__u32		op_flags;
 
-	__u32		nr_sectors;
+	union {
+		__u32		nr_sectors;
+		__u32		nr_zones; /* for UBLK_IO_OP_REPORT_ZONES only */
+	};
 
 	/* start sector for this io */
 	__u64		start_sector;
@@ -308,6 +313,12 @@ struct ublksrv_io_cmd {
 	/*
 	 * userspace buffer address in ublksrv daemon process, valid for
 	 * FETCH* command only
+	 *
+	 * This field shouldn't be used if UBLK_F_USER_COPY is enabled,
+	 * because userspace deals with data copy by pread()/pwrite() over
+	 * /dev/ublkcN. But in case of UBLK_F_ZONED, 'addr' is re-used to
+	 * pass back the allocated LBA for UBLK_IO_OP_ZONE_APPEND which
+	 * actually depends on UBLK_F_USER_COPY
 	 */
 	__u64	addr;
 };

Thanks,
Ming