Re: [PATCH] block: emit disk ro uevent in device_add_disk()

[Christoph Hellwig <hch@infradead.org>]

On Thu, Mar 03, 2022 at 10:52:20AM -0700, Uday Shankar wrote:
> Userspace learns of disk ro state via the change event emitted by
> set_disk_ro_uevent. This function has cyclic dependency with
> device_add_disk: the latter performs kobject initialization that is
> necessary for uevents to go through, but we want to set up properties
> like ro state before exposing the disk to userspace via device_add_disk.
> 
> The usual workaround is to call set_disk_ro both before and after
> device_add_disk; the purpose of the "after" call is just to emit the
> uevent. Moreover, because set_disk_ro only emits a uevent when the ro
> state changes, set_disk_ro needs to be called twice in the "after"
> position to ensure that the ro state flips. See drivers/scsi/sd.c for an
> example of this pattern.

I don't see any such pattern there.  I also don't see what the point
is.  KOBJ_CHANGE uevents tell about a change in device state.  But
if a device is marked read-only before disk_add that read-only
state is already visible by the time the device is added and thus
shows up in sysfs, and we do not need an extra notification.