Re: [PATCH v2] ublk: Add UBLK_U_CMD_UPDATE_SIZE

[Ming Lei <ming.lei@redhat.com>]

On Thu, Apr 10, 2025 at 03:29:38PM +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.
> 
> 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      | 23 ++++++++++++++++++++++-
>  include/uapi/linux/ublk_cmd.h |  7 +++++++
>  2 files changed, 29 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index 2fd05c1bd30b..acf8aa6c4452 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 \
> @@ -3052,6 +3053,22 @@ static int ublk_ctrl_get_features(struct io_uring_cmd
> *cmd)
>         return 0;
>  }
> 
> +static int ublk_ctrl_set_size(struct ublk_device *ub,
> +               struct io_uring_cmd *cmd)
> +{
> +       const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
> +       struct ublk_param_basic *p = &ub->params.basic;
> +       size_t new_size = (int)header->data[0];
> +       int ret = 0;
> +
> +       p->dev_sectors = new_size;

The above line need to be protected by ub->mutex.


thanks,
Ming