Re: [PATCH v2 2/2] ublk: add UBLK_CMD_TRY_STOP_DEV command

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

On Sun, Jan 04, 2026 at 10:48:39AM +0200, Yoav Cohen wrote:
> This command is similar to UBLK_CMD_STOP_DEV, but it only stops the
> device if there are no active openers for the ublk block device.
> If the device is busy, the command returns -EBUSY instead of
> disrupting active clients. This allows safe, non-destructive stopping.
> 
> Signed-off-by: Yoav Cohen <yoav@nvidia.com>
> ---
>  drivers/block/ublk_drv.c      | 42 +++++++++++++++++++++++++++++++++++
>  include/uapi/linux/ublk_cmd.h |  3 ++-
>  2 files changed, 44 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index 2d5602ef05cc..55a5ab11c1cd 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -54,6 +54,7 @@
>  #define UBLK_CMD_DEL_DEV_ASYNC	_IOC_NR(UBLK_U_CMD_DEL_DEV_ASYNC)
>  #define UBLK_CMD_UPDATE_SIZE	_IOC_NR(UBLK_U_CMD_UPDATE_SIZE)
>  #define UBLK_CMD_QUIESCE_DEV	_IOC_NR(UBLK_U_CMD_QUIESCE_DEV)
> +#define UBLK_CMD_TRY_STOP_DEV	_IOC_NR(UBLK_U_CMD_TRY_STOP_DEV)

This need a feature flag, such as UBLK_F_SAFE_STOP, which is set in
ublk_ctrl_add_dev(), meantime document that UBLK_CMD_TRY_STOP_DEV is
supported with this feature.

>  
>  #define UBLK_IO_REGISTER_IO_BUF		_IOC_NR(UBLK_U_IO_REGISTER_IO_BUF)
>  #define UBLK_IO_UNREGISTER_IO_BUF	_IOC_NR(UBLK_U_IO_UNREGISTER_IO_BUF)
> @@ -239,6 +240,8 @@ struct ublk_device {
>  	struct delayed_work	exit_work;
>  	struct work_struct	partition_scan_work;
>  
> +	bool			block_open; /* protected by open_mutex */
> +
>  	struct ublk_queue       *queues[];
>  };
>  
> @@ -919,6 +922,9 @@ static int ublk_open(struct gendisk *disk, blk_mode_t mode)
>  			return -EPERM;
>  	}
>  
> +	if (ub->block_open)
> +		return -EBUSY;
> +
>  	return 0;
>  }
>  
> @@ -3309,6 +3315,38 @@ static void ublk_ctrl_stop_dev(struct ublk_device *ub)
>  	ublk_stop_dev(ub);
>  }
>  
> +static int ublk_ctrl_try_stop_dev(struct ublk_device *ub)
> +{
> +	struct gendisk *disk;
> +	int ret = -EINVAL;

-EINVAL is never used, it may save the line of `ret = 0` if it is
initialized as 0.

> +
> +	disk = ublk_get_disk(ub);
> +	if (!disk) {
> +		ret = -ENODEV;
> +		goto out;

		return -ENODEV;


Thanks, 
Ming