Re: [PATCH 1/4] ublk: cleanup flag handling and fix UBLK_F_NO_AUTO_PART_SCAN

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

On Mon, Feb 23, 2026 at 12:15:11PM +0000, Alexander Atanasov wrote:
> Currently the code misuse GD_SUPPRESS_PART_SCAN flag
> as it tries to use it as a switch for the auto partition scan.
> To fully disable creation of partitions GENHD_FL_NO_PART must
> be used, switch code to use it instead GD_SUPPRESS_PART_SCAN.
> 
> Using the new flags rules for partitions become:
>  - Unprivileged daemons - never scan partitions, they have
> GENHD_FL_NO_PART always set - they are devices without partitions.
> 
>  - Trusted daemons - by default have partitions disabled.
> Partitions can be enabled via UBLK_F_PARTITIONS flag and
> automatic initial scan can be requested via UBLK_F_AUTO_PART_SCAN flag.
> 
> Rework the code to work as described above:
> - remove checks in ublk_partition_scan_work and rely on
> the caller to schedule the work only if it has to be done.
> - set GENHD_FL_NO_PART on unprivileged devices
> - set GENHD_FL_NO_PART depending on UBLK_F_PARTITIONS on trusted
> devices.
> 
> Fixes: 8443e2087e70 ("ublk: add UBLK_F_NO_AUTO_PART_SCAN feature flag")
> Signed-off-by: Alexander Atanasov <alex@zazolabs.com>
> ---
>  drivers/block/ublk_drv.c      | 34 +++++++++++++++++++---------------
>  include/uapi/linux/ublk_cmd.h |  7 +++++--
>  2 files changed, 24 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index 3c918db4905c..d0c646eb9435 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -81,7 +81,8 @@
>  		| (IS_ENABLED(CONFIG_BLK_DEV_INTEGRITY) ? UBLK_F_INTEGRITY : 0) \
>  		| UBLK_F_SAFE_STOP_DEV \
>  		| UBLK_F_BATCH_IO \
> -		| UBLK_F_NO_AUTO_PART_SCAN)
> +		| UBLK_F_PARTITIONS \
> +		| UBLK_F_AUTO_PART_SCAN)
>  
>  #define UBLK_F_ALL_RECOVERY_FLAGS (UBLK_F_USER_RECOVERY \
>  		| UBLK_F_USER_RECOVERY_REISSUE \
> @@ -2361,14 +2362,9 @@ static void ublk_partition_scan_work(struct work_struct *work)
>  	if (!disk)
>  		return;
>  
> -	if (WARN_ON_ONCE(!test_and_clear_bit(GD_SUPPRESS_PART_SCAN,
> -					     &disk->state)))
> -		goto out;
> -
>  	mutex_lock(&disk->open_mutex);
>  	bdev_disk_changed(disk, false);
>  	mutex_unlock(&disk->open_mutex);
> -out:
>  	ublk_put_disk(disk);
>  }
>  
> @@ -4409,9 +4405,13 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub,
>  	 * wait while holding ub->mutex, which can deadlock with other
>  	 * operations that need the mutex. Defer partition scan to async
>  	 * work.
> -	 * For unprivileged daemons, keep GD_SUPPRESS_PART_SCAN set
> -	 * permanently.
> +	 * For unprivileged daemons, set GENHD_FL_NO_PART to
> +	 * disable partitions.
>  	 */
> +	if (ub->unprivileged_daemons)
> +		disk->flags |= GENHD_FL_NO_PART;

The above code block can cover UBLK_F_PARTITIONS too.

> +
> +	/* Disable partition scans */
>  	set_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
>  
>  	ublk_get_device(ub);
> @@ -4429,13 +4429,17 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub,
>  
>  	set_bit(UB_STATE_USED, &ub->state);
>  
> -	/* Skip partition scan if disabled by user */
> -	if (ub->dev_info.flags & UBLK_F_NO_AUTO_PART_SCAN) {
> -		clear_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
> -	} else {
> -		/* Schedule async partition scan for trusted daemons */
> -		if (!ub->unprivileged_daemons)
> -			schedule_work(&ub->partition_scan_work);
> +	if (!ub->unprivileged_daemons) {
> +		if (!(ub->dev_info.flags & UBLK_F_PARTITIONS)) {
> +			/* disable partitions on trusted device */
> +			disk->flags |= GENHD_FL_NO_PART;
> +		} else {
> +			/* Enable partition scan on device */
> +			clear_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
> +			/* Schedule auto partition scan if requested */
> +			if (ub->dev_info.flags & UBLK_F_AUTO_PART_SCAN)
> +				schedule_work(&ub->partition_scan_work);
> +		}
>  	}
>  
>  out_put_cdev:
> diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
> index a88876756805..467ecaa20ac1 100644
> --- a/include/uapi/linux/ublk_cmd.h
> +++ b/include/uapi/linux/ublk_cmd.h
> @@ -367,8 +367,11 @@
>   */
>  #define UBLK_F_SAFE_STOP_DEV	(1ULL << 17)
>  
> -/* Disable automatic partition scanning when device is started */
> -#define UBLK_F_NO_AUTO_PART_SCAN (1ULL << 18)
> +/* Enable partitions on the device */
> +#define UBLK_F_PARTITIONS (1ULL << 18)
> +
> +/* Perform automatic partition scanning when device is started */
> +#define UBLK_F_AUTO_PART_SCAN (1ULL << 19)

I think it isn't necessary to add UBLK_F_AUTO_PART_SCAN, and the default
behavior is to scan partitions automatically just like other block device.


Thanks,
Ming