On Sat, Dec 20, 2025 at 4:53 AM Ming Lei ming.lei@redhat.com wrote:

Add a new feature flag UBLK_F_NO_AUTO_PART_SCAN to allow users to suppress automatic partition scanning when starting a ublk device.

Is this approach superseded by your patch series "ublk: scan partition in async way", or are you expecting both to coexist?

This is useful for network-backed devices where partition scanning can cause issues:

• Partition scan triggers synchronous I/O during device startup
• If userspace server crashes during scan, recovery is problematic
• For remotely-managed devices, partition probing may not be needed

Users can manually trigger partition scanning later when appropriate using standard tools (e.g., partprobe, blockdev --rereadpt).

Reported-by: Yoav Cohen yoav@nvidia.com Link: https://lore.kernel.org/linux-block/DM4PR12MB63280C5637917C071C2F0D65A9A8A@D... Cc: stable@vger.kernel.org Signed-off-by: Ming Lei ming.lei@redhat.com

---

• suggest to backport to stable, which is useful for avoiding problematic recovery, also the change is simple enough

Not sure backporting to stable makes sense. It's a new feature that requires the ublk server to opt in, so any existing ublk server being used on a stable kernel won't be able to make use of it.

drivers/block/ublk_drv.c | 16 +++++++++++++--- include/uapi/linux/ublk_cmd.h | 8 ++++++++ 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c index 78f3e22151b9..ca6ec8ed443f 100644 --- a/drivers/block/ublk_drv.c +++ b/drivers/block/ublk_drv.c @@ -73,7 +73,8 @@ | UBLK_F_AUTO_BUF_REG \ | UBLK_F_QUIESCE \ | UBLK_F_PER_IO_DAEMON \

•           | UBLK_F_BUF_REG_OFF_DAEMON)
  

•           | UBLK_F_BUF_REG_OFF_DAEMON \
  

•           | UBLK_F_NO_AUTO_PART_SCAN)
  
  

#define UBLK_F_ALL_RECOVERY_FLAGS (UBLK_F_USER_RECOVERY \ | UBLK_F_USER_RECOVERY_REISSUE \ @@ -2930,8 +2931,13 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub,

    ublk_apply_params(ub);

•   /* don't probe partitions if any daemon task is un-trusted */
  

•   if (ub->unprivileged_daemons)
  

•   /*
  

•    * Don't probe partitions if:
  

•    * - any daemon task is un-trusted, or
  

•    * - user explicitly requested to suppress partition scan
  

•    */
  

•   if (ub->unprivileged_daemons ||
  

•       (ub->dev_info.flags & UBLK_F_NO_AUTO_PART_SCAN))
            set_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
  
    ublk_get_device(ub);
  

@@ -2947,6 +2953,10 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub, if (ret) goto out_put_cdev;

•   /* allow user to probe partitions from userspace */
  

•   if (!ub->unprivileged_daemons &&
  

•       (ub->dev_info.flags & UBLK_F_NO_AUTO_PART_SCAN))
  

•           clear_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
    set_bit(UB_STATE_USED, &ub->state);
  
  

out_put_cdev: diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h index ec77dabba45b..0827db14a215 100644 --- a/include/uapi/linux/ublk_cmd.h +++ b/include/uapi/linux/ublk_cmd.h @@ -311,6 +311,14 @@ */ #define UBLK_F_BUF_REG_OFF_DAEMON (1ULL << 14)

+/*

• • If this feature is set, the kernel will not automatically scan for partitions
• • when the device is started. This is useful for network-backed devices where
• • partition scanning can cause deadlocks if the userspace server crashes during
• • the scan. Users can manually trigger partition scanning later when appropriate.
• */

+#define UBLK_F_NO_AUTO_PART_SCAN (1ULL << 15)

This is the same bit you've used for UBLK_F_BATCH_IO in your other patch series. Are you planning to change that one?

Best, Caleb

/* device state */ #define UBLK_S_DEV_DEAD 0

#define UBLK_S_DEV_LIVE 1

2.47.0