Re: [PATCH v2] block: ublk: enable zoned storage support

[Niklas Cassel]

On Fri, Feb 24, 2023 at 09:05:01PM +0100, Andreas Hindborg wrote:
> 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
> 
> This allows implementation of zoned storage devices in user space. An
> example user space implementation based on ubdsrv is available [1].
> 
> [1] https://github.com/metaspace/ubdsrv/commit/14a2b708f74f70cfecb076d92e680dc718cc1f6d
> 
> Signed-off-by: Andreas Hindborg <a.hindborg@xxxxxxxxxxx>
> ---
> Changes since v1:
>  - Fixed conditional compilation bug
>  - Refactored to collect conditional code additions together
>  - Fixed style errors
>  - Zero stack allocated value used for zone report
> 
> Reported-by: Niklas Cassel <Niklas.Cassel@xxxxxxx>
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Link: https://lore.kernel.org/oe-kbuild-all/202302250222.XOrw9j6z-lkp@xxxxxxxxx/
> v1: https://lore.kernel.org/linux-block/20230224125950.214779-1-nmi@xxxxxxxxxxxx/
> 
>  drivers/block/ublk_drv.c      | 150 ++++++++++++++++++++++++++++++++--
>  include/uapi/linux/ublk_cmd.h |  18 ++++
>  2 files changed, 162 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index 6368b56eacf1..37e516903867 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -20,6 +20,7 @@
>  #include <linux/major.h>
>  #include <linux/wait.h>
>  #include <linux/blkdev.h>
> +#include <linux/blkzoned.h>
>  #include <linux/init.h>
>  #include <linux/swap.h>
>  #include <linux/slab.h>
> @@ -51,10 +52,12 @@
>  		| UBLK_F_URING_CMD_COMP_IN_TASK \
>  		| UBLK_F_NEED_GET_DATA \
>  		| UBLK_F_USER_RECOVERY \
> -		| UBLK_F_USER_RECOVERY_REISSUE)
> +		| UBLK_F_USER_RECOVERY_REISSUE \
> +		| UBLK_F_ZONED)
>  
>  /* All UBLK_PARAM_TYPE_* should be included here */
> -#define UBLK_PARAM_TYPE_ALL (UBLK_PARAM_TYPE_BASIC | UBLK_PARAM_TYPE_DISCARD)
> +#define UBLK_PARAM_TYPE_ALL (UBLK_PARAM_TYPE_BASIC | UBLK_PARAM_TYPE_DISCARD \
> +			     | UBLK_PARAM_TYPE_ZONED)
>  
>  struct ublk_rq_data {
>  	struct llist_node node;
> @@ -187,6 +190,98 @@ static DEFINE_MUTEX(ublk_ctl_mutex);
>  
>  static struct miscdevice ublk_misc;
>  
> +#ifdef CONFIG_BLK_DEV_ZONED
> +static void ublk_set_nr_zones(struct ublk_device *ub)
> +{
> +	const struct ublk_param_basic *p = &ub->params.basic;
> +
> +	if (ub->dev_info.flags & UBLK_F_ZONED && p->chunk_sectors)
> +		ub->ub_disk->nr_zones = p->dev_sectors / p->chunk_sectors;
> +}
> +
> +static void ublk_dev_param_zoned_apply(struct ublk_device *ub)
> +{
> +	const struct ublk_param_zoned *p = &ub->params.zoned;
> +
> +	if (ub->dev_info.flags & UBLK_F_ZONED) {
> +		disk_set_max_active_zones(ub->ub_disk, p->max_active_zones);
> +		disk_set_max_open_zones(ub->ub_disk, p->max_open_zones);
> +	}
> +}
> +
> +static int ublk_revalidate_disk_zones(struct gendisk *disk)
> +{
> +	return blk_revalidate_disk_zones(disk, NULL);
> +}
> +
> +static int ublk_report_zones(struct gendisk *disk, sector_t sector,
> +			     unsigned int nr_zones, report_zones_cb cb,
> +			     void *data)
> +{
> +	struct ublk_device *ub;
> +	unsigned int zone_size;
> +	unsigned int first_zone;
> +	int ret = 0;
> +
> +	ub = disk->private_data;
> +
> +	if (!(ub->dev_info.flags & UBLK_F_ZONED))
> +		return -EINVAL;
> +
> +	zone_size = disk->queue->limits.chunk_sectors;
> +	first_zone = sector >> ilog2(zone_size);
> +	nr_zones = min(ub->ub_disk->nr_zones - first_zone, nr_zones);
> +
> +	for (unsigned int i = 0; i < nr_zones; i++) {
> +		struct request *req;
> +		blk_status_t status;
> +		struct blk_zone info = {0};
> +
> +		req = blk_mq_alloc_request(disk->queue, REQ_OP_DRV_IN, 0);
> +
> +		if (IS_ERR(req)) {
> +			ret = PTR_ERR(req);
> +			goto out;
> +		}
> +
> +		req->__sector = sector;
> +
> +		ret = blk_rq_map_kern(disk->queue, req, &info, sizeof(info),
> +				      GFP_KERNEL);
> +
> +		if (ret)
> +			goto out;
> +
> +		status = blk_execute_rq(req, 0);
> +		ret = blk_status_to_errno(status);
> +		if (ret)
> +			goto out;
> +
> +		blk_mq_free_request(req);
> +
> +		ret = cb(&info, i, data);
> +		if (ret)
> +			goto out;
> +
> +		/* A zero length zone means don't ask for more zones */
> +		if (!info.len) {
> +			nr_zones = i;
> +			break;
> +		}
> +
> +		sector += zone_size;
> +	}
> +	ret = nr_zones;
> +
> + out:
> +	return ret;
> +}
> +#else
> +void ublk_set_nr_zones(struct ublk_device *ub);
> +void ublk_dev_param_zoned_apply(struct ublk_device *ub);
> +int ublk_revalidate_disk_zones(struct gendisk *disk);

These are declarations, shouldn't they be dummy definitions instead?

e.g.
static int ublk_revalidate_disk_zones(struct gendisk *disk) { return -EOPNOTSUPP; };


It would be nice if they could be avoided altogether.

Looking how e.g. null-blk and btrfs has solved this:
https://github.com/torvalds/linux/blob/v6.2/fs/btrfs/Makefile#L39
https://github.com/torvalds/linux/blob/v6.2/drivers/block/null_blk/Makefile#L11

They have put the zoned stuff in a separate C file that is only compiled
when CONFIG_BLK_DEV_ZONED is set.

I'm not sure if a similar design is desired for ublk or not.

However, if a similar design pattern was used, it could probably avoid
some of these unpleasant dummy definitions altogether.


Kind regards,
Niklas

> +#endif
> +