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

[Ming Lei]

On Wed, Jul 19, 2023 at 05:26:11PM +0800, Ming Lei wrote:
> 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;

Or use union to cover zoned_append_lba, and we still need above
document about UBLK_F_USER_COPY & UBLK_F_ZONED uses.

	union {
		__u64	addr;
		__u64	zoned_append_lba;
	}


Thanks,
Ming