Re: [PATCH v4]: ublk: Add UBLK_U_CMD_UPDATE_SIZE

[Uday Shankar <ushankar@purestorage.com>]

On Wed, Apr 16, 2025 at 01:07:47PM +0300, Jared Holzman wrote:
> Currently ublk only allows the size of the ublkb block device to be
> set via UBLK_CMD_SET_PARAMS before UBLK_CMD_START_DEV is triggered.
> 
> This does not provide support for extendable user-space block devices
> without having to stop and restart the underlying ublkb block device
> causing IO interruption.
> 
> This patch adds a new ublk command UBLK_U_CMD_UPDATE_SIZE to allow the
> ublk block device to be resized on-the-fly.

Many of the other parameters in ublk_params/ublksrv_ctrl_dev_info could
also feasibly be changed after initial device creation/start. Is it
possible to design the API in a way so that we don't have to have one
command per parameter?

> Feature flag UBLK_F_UPDATE_SIZE is also added to indicate support for this
> command.
> 
> Signed-off-by: Omri Mann <omri@nvidia.com>
> ---
>  drivers/block/ublk_drv.c      | 18 +++++++++++++++++-
>  include/uapi/linux/ublk_cmd.h |  7 +++++++
>  2 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index cdb1543fa4a9..128f094efbad 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -64,7 +64,8 @@
>          | UBLK_F_CMD_IOCTL_ENCODE \
>          | UBLK_F_USER_COPY \
>          | UBLK_F_ZONED \
> -        | UBLK_F_USER_RECOVERY_FAIL_IO)
> +        | UBLK_F_USER_RECOVERY_FAIL_IO \
> +        | UBLK_F_UPDATE_SIZE)
> 
>  #define UBLK_F_ALL_RECOVERY_FLAGS (UBLK_F_USER_RECOVERY \
>          | UBLK_F_USER_RECOVERY_REISSUE \
> @@ -3067,6 +3068,16 @@ static int ublk_ctrl_get_features(const struct
> ublksrv_ctrl_cmd *header)
>      return 0;
>  }
> 
> +static void ublk_ctrl_set_size(struct ublk_device *ub, const struct
> ublksrv_ctrl_cmd *header)
> +{
> +    struct ublk_param_basic *p = &ub->params.basic;
> +    u64 new_size = header->data[0];
> +
> +    mutex_lock(&ub->mutex);
> +    p->dev_sectors = new_size;
> +    set_capacity_and_notify(ub->ub_disk, p->dev_sectors);
> +    mutex_unlock(&ub->mutex);
> +}
>  /*
>   * All control commands are sent via /dev/ublk-control, so we have to check
>   * the destination device's permission
> @@ -3152,6 +3163,7 @@ static int ublk_ctrl_uring_cmd_permission(struct
> ublk_device *ub,
>      case UBLK_CMD_SET_PARAMS:
>      case UBLK_CMD_START_USER_RECOVERY:
>      case UBLK_CMD_END_USER_RECOVERY:
> +    case _IOC_NR(UBLK_U_CMD_UPDATE_SIZE):
>          mask = MAY_READ | MAY_WRITE;
>          break;
>      default:
> @@ -3243,6 +3255,10 @@ static int ublk_ctrl_uring_cmd(struct io_uring_cmd
> *cmd,
>      case UBLK_CMD_END_USER_RECOVERY:
>          ret = ublk_ctrl_end_recovery(ub, header);
>          break;
> +    case _IOC_NR(UBLK_U_CMD_UPDATE_SIZE):
> +        ublk_ctrl_set_size(ub, header);
> +        ret = 0;
> +        break;
>      default:
>          ret = -EOPNOTSUPP;
>          break;
> diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
> index 583b86681c93..587a54b3cfe1 100644
> --- a/include/uapi/linux/ublk_cmd.h
> +++ b/include/uapi/linux/ublk_cmd.h
> @@ -51,6 +51,8 @@
>      _IOR('u', 0x13, struct ublksrv_ctrl_cmd)
>  #define UBLK_U_CMD_DEL_DEV_ASYNC    \
>      _IOR('u', 0x14, struct ublksrv_ctrl_cmd)
> +#define UBLK_U_CMD_UPDATE_SIZE        \
> +    _IOWR('u', 0x15, struct ublksrv_ctrl_cmd)
> 
>  /*
>   * 64bits are enough now, and it should be easy to extend in case of
> @@ -211,6 +213,11 @@
>   */
>  #define UBLK_F_USER_RECOVERY_FAIL_IO (1ULL << 9)
> 
> +/*
> + * Resizing a block device is possible with UBLK_U_CMD_UPDATE_SIZE
> + */
> +#define UBLK_F_UPDATE_SIZE         (1ULL << 10)
> +
>  /* device state */
>  #define UBLK_S_DEV_DEAD    0
>  #define UBLK_S_DEV_LIVE    1
> -- 
> 2.43.0
> 
>