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

[Ramesh Errabolu <ramesh@linux.ibm.com>]

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