Re: [PATCH v1] PCI: Add write-only 'uevent' sysfs attribute for PCI slots

[Ramesh Errabolu]

On 2/26/2026 12:39 PM, Leon Romanovsky wrote:
> On Thu, Feb 26, 2026 at 11:53:32AM -0600, Ramesh Errabolu wrote:
> > On 2/26/2026 2:34 AM, Leon Romanovsky wrote:
> > > On Wed, Feb 25, 2026 at 09:08:15AM -0600, Ramesh Errabolu wrote:
> > > > Add a new write-only 'uevent' attribute to PCI slot sysfs
> > > > entries. This provides a mechanism for userspace to explicitly
> > > > synthesize PCI slot uevents when needed.
> > > >
> > > > For cold-plugged PCI devices, slots may be created before
> > > > udev is ready to receive events, causing the initial 'add'
> > > > uevents to be missed. As a result, slot specific udev
> > > > rules that define naming, permissions, and related policies,
> > > > are not applied at boot. Allowing userspace to resynthesize
> > > > the 'add' uevent ensures these rules are processed correctly.
> > > This patch sounds like a hack to me. AFAIK, "udevadm trigger"
> > > performs exactly that.
> > >
> > > Thanks
> > AFAIK, PCI slots do not yet raise a uevent.
> Right
>
> > Secondly there is no uevent attribute in slot-id directory to submit requests to raise a uevent. This
> > patch fills that gap
> Please start from the beginning and explain what you mean by 'the gap'.
> Which scenario failed before and began working after this patch? From your
> description, it sounds like the behavior should already be covered by the
> 'udevadm trigger' command.
>
> I want to note that drivers/pci/slot.c has remained largely unchanged since 2008.
>
> Thanks
PCI slots are surfaced early in the boot process before udev daemon is 
able to run and process these uevents. As a consequence any uevents 
raised by PCI slots are lost. To apply the relevant udev rules, we need 
to raise PCI slot uevents a second time. This cannot happen if uevent 
attribute is not surface by PCI slots.

To me the sequence is as follows:

- udevadm submits a request to raise a PCI Slot uevent
- PCI slot uevent handler constructs and publishes a uevent to userspace
- udev daemon receives the uevent and processes it i.e. apply 
configuration encoded by matching udev rules