Re: ublk invert part scan bit logic

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

On Thu, Feb 12, 2026 at 05:48:40AM -0700, Jens Axboe wrote:
> On 2/12/26 5:42 AM, Ming Lei wrote:
> > On Thu, Feb 12, 2026 at 04:05:27AM -0700, Jens Axboe wrote:
> >> Hi,
> >>
> >> For ublk, there's this logic in in ublk_ctrl_start_dev():
> >>
> >> /* 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);
> >> }
> >>
> >> where the
> >>
> >> clear_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
> >>
> >> seems reversed? Why is GD_SUPPRESS_PART_SCAN being cleared if
> >> UBLK_F_NO_AUTO_PART_SCAN is set? Added in:
> >>
> >> 8443e2087e70 ("ublk: add UBLK_F_NO_AUTO_PART_SCAN feature flag")
> > 
> > Yeah, the interface is designed in this way: partition scan is not
> > done during add disk, and allowed since then on. The selftest code
> > is written in same way too.
> > 
> > If GD_SUPPRESS_PART_SCAN isn't cleared, userspace can't probe partitions
> > any more.
> > 
> > However, if you think the interface isn't good, we still can change it
> > before 7.0 release.
> 
> What I mean is, if UBLK_F_NO_AUTO_PART_SCAN is set, should we not
> either leave the disk->state alone, or _set_ GD_SUPPRESS_PART_SCAN?

UBLK_F_NO_AUTO_PART_SCAN means partition scanning isn't done automatically
from add_disk(), but it still allow userspace to send ioctl(BLKRRPART) for
probing partition since disk is added.

If GD_SUPPRESS_PART_SCAN is set, ioctl(BLKRRPART) can't succeed any more.

> I might be confused here, but the current implementation doesn't
> make much sense to me! If it is correct, then a comment to that
> effect would be good imho.

I admit it is a little confusing, will send a patch to document this
behavior if no one objects the UAPI.


Thanks,
Ming