[PATCH v2 0/1] PCI/hotplug: Add 'uevent' sysfs attribute to trigger slot events

[PATCH v2 0/1] PCI/hotplug: Add 'uevent' sysfs attribute to trigger slot events

[Ramesh Errabolu]

Hi all,

This is v2 of the patch adding write-only uevent
support for PCI slots. The original v1 was posted
in February 2026 and received valuable feedback from
Leon Romanovsky and others. This v2 addresses the feedback
and is rebased onto the current kernel tree.

    Link to v1:
    https://lore.kernel.org/all/20260225150815.81268-1-ramesh@linux.ibm.com/

Testing: Tested on s390x with multiple PCI slots
 - Write-only uevent attribute is created for each slot
 - Writing "add" triggers proper uevent generation
 - udevadm-trigger successfully generates slot uevents
 - Events are properly received by udev monitoring tools

Changes since v1 (February 2026):
 - Improved commit message clarity, per reviewer feedback
 - Rebased onto current kernel tree (v7.x)

Ramesh Errabolu (1):
  PCI/hotplug: Add 'uevent' sysfs attribute to trigger slot events

 drivers/pci/hotplug/pci_hotplug_core.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

-- 
2.43.0

[PATCH v2 1/1] PCI/hotplug: Add 'uevent' sysfs attribute to trigger slot events

[Ramesh Errabolu]

Add a write-only 'uevent' sysfs attribute for synthesizing
uevents for a PCI slot. This extends the existing uevent
support which emits a KOBJ_ADD uevent in pci_hp_add() with
the ability to replay such uevents for cold plugged devices.
As such events are only emitted by hotplug capable PCI slots
so is the support for synthesizing them.

The change was validated by manually triggering 'add' uevent
for a specific hotplug PCI slot:

    $ echo "add $(uuidgen)" | sudo tee   \
                /sys/bus/pci/slots/<slot-id>/uevent

Signed-off-by: Ramesh Errabolu <ramesh@linux.ibm.com>
---
 drivers/pci/hotplug/pci_hotplug_core.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/drivers/pci/hotplug/pci_hotplug_core.c b/drivers/pci/hotplug/pci_hotplug_core.c
index fadcf98a8a66..c3634b1cc7a8 100644
--- a/drivers/pci/hotplug/pci_hotplug_core.c
+++ b/drivers/pci/hotplug/pci_hotplug_core.c
@@ -176,6 +176,21 @@ static struct pci_slot_attribute hotplug_slot_attr_presence = {
 	.show = presence_read_file,
 };
 
+static ssize_t uevent_write_file(struct pci_slot *slot,
+				 const char *buf, size_t len)
+{
+	int rc;
+
+	rc = kobject_synth_uevent(&slot->kobj, buf, len);
+	return rc ? rc : len;
+}
+
+static struct pci_slot_attribute hotplug_slot_attr_uevent = {
+	.attr = {.name = "uevent", .mode = S_IFREG | 0200},
+	.show = NULL,
+	.store = uevent_write_file
+};
+
 static ssize_t test_write_file(struct pci_slot *pci_slot, const char *buf,
 			       size_t count)
 {
@@ -254,6 +269,11 @@ static int fs_add_slot(struct hotplug_slot *slot, struct pci_slot *pci_slot)
 		kobject_put(kobj);
 	}
 
+	retval = sysfs_create_file(&pci_slot->kobj,
+				   &hotplug_slot_attr_uevent.attr);
+	if (retval)
+		goto exit_uevent;
+
 	if (has_power_file(slot)) {
 		retval = sysfs_create_file(&pci_slot->kobj,
 					   &hotplug_slot_attr_power.attr);
@@ -306,6 +326,9 @@ static int fs_add_slot(struct hotplug_slot *slot, struct pci_slot *pci_slot)
 	if (has_power_file(slot))
 		sysfs_remove_file(&pci_slot->kobj, &hotplug_slot_attr_power.attr);
 exit_power:
+	sysfs_remove_file(&pci_slot->kobj,
+			  &hotplug_slot_attr_uevent.attr);
+exit_uevent:
 	sysfs_remove_link(&pci_slot->kobj, "module");
 exit:
 	return retval;
@@ -313,6 +336,8 @@ static int fs_add_slot(struct hotplug_slot *slot, struct pci_slot *pci_slot)
 
 static void fs_remove_slot(struct hotplug_slot *slot, struct pci_slot *pci_slot)
 {
+	sysfs_remove_file(&pci_slot->kobj, &hotplug_slot_attr_uevent.attr);
+
 	if (has_power_file(slot))
 		sysfs_remove_file(&pci_slot->kobj, &hotplug_slot_attr_power.attr);
 
-- 
2.43.0

Re: [PATCH v2 1/1] PCI/hotplug: Add 'uevent' sysfs attribute to trigger slot events

[Niklas Schnelle]

On Thu, 2026-04-16 at 16:39 -0500, Ramesh Errabolu wrote:
> Add a write-only 'uevent' sysfs attribute for synthesizing
> uevents for a PCI slot. This extends the existing uevent
> support which emits a KOBJ_ADD uevent in pci_hp_add() with
> the ability to replay such uevents for cold plugged devices.
> As such events are only emitted by hotplug capable PCI slots
> so is the support for synthesizing them.
> 
> The change was validated by manually triggering 'add' uevent
> for a specific hotplug PCI slot:
> 
>     $ echo "add $(uuidgen)" | sudo tee   \
>                 /sys/bus/pci/slots/<slot-id>/uevent
> 
> Signed-off-by: Ramesh Errabolu <ramesh@linux.ibm.com>
> ---
>  drivers/pci/hotplug/pci_hotplug_core.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 

Sorry for the review delay. This looks good to me and will really help
with udev rule execution for devices which are discovered in standby
state during boot and thus currently don't create any uevents. Of
course to work by default this still requires a systemd/udev addition
that I know you're also working on. 

Consequently, I tested the uevent synthesization with both slots with a
configured (slot powered on) and standby (slot powered off) PCI
function.

Feel free to add:

Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>

Thanks,
Niklas

Re: [PATCH v2 1/1] PCI/hotplug: Add 'uevent' sysfs attribute to trigger slot events

[Ramesh Errabolu]

Thanks for testing and also giving me the review-by

Regards,
Ramesh


On 4/17/2026 4:53 AM, Niklas Schnelle wrote:
> On Thu, 2026-04-16 at 16:39 -0500, Ramesh Errabolu wrote:
>> Add a write-only 'uevent' sysfs attribute for synthesizing
>> uevents for a PCI slot. This extends the existing uevent
>> support which emits a KOBJ_ADD uevent in pci_hp_add() with
>> the ability to replay such uevents for cold plugged devices.
>> As such events are only emitted by hotplug capable PCI slots
>> so is the support for synthesizing them.
>>
>> The change was validated by manually triggering 'add' uevent
>> for a specific hotplug PCI slot:
>>
>>      $ echo "add $(uuidgen)" | sudo tee   \
>>                  /sys/bus/pci/slots/<slot-id>/uevent
>>
>> Signed-off-by: Ramesh Errabolu <ramesh@linux.ibm.com>
>> ---
>>   drivers/pci/hotplug/pci_hotplug_core.c | 25 +++++++++++++++++++++++++
>>   1 file changed, 25 insertions(+)
>>
> Sorry for the review delay. This looks good to me and will really help
> with udev rule execution for devices which are discovered in standby
> state during boot and thus currently don't create any uevents. Of
> course to work by default this still requires a systemd/udev addition
> that I know you're also working on.
>
> Consequently, I tested the uevent synthesization with both slots with a
> configured (slot powered on) and standby (slot powered off) PCI
> function.
>
> Feel free to add:
>
> Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
> Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>
>
> Thanks,
> Niklas

Re: [PATCH v2 1/1] PCI/hotplug: Add 'uevent' sysfs attribute to trigger slot events

[Krzysztof Wilczyński]

Hello,

> +static struct pci_slot_attribute hotplug_slot_attr_uevent = {
> +	.attr = {.name = "uevent", .mode = S_IFREG | 0200},
> +	.show = NULL,
> +	.store = uevent_write_file
> +};

I think, you could use the __ATTR_WO() macro here.

Thank you!

	Krzysztof

Re: [PATCH v2 1/1] PCI/hotplug: Add 'uevent' sysfs attribute to trigger slot events

[Ramesh Errabolu]

On 4/21/2026 12:13 PM, Krzysztof Wilczyński wrote:

> Hello,
>
>> +static struct pci_slot_attribute hotplug_slot_attr_uevent = {
>> +	.attr = {.name = "uevent", .mode = S_IFREG | 0200},
>> +	.show = NULL,
>> +	.store = uevent_write_file
>> +};
> I think, you could use the __ATTR_WO() macro here.
Use of the suggested macro is not appropriate
>
> Thank you!
>
> 	Krzysztof

Re: [PATCH v2 1/1] PCI/hotplug: Add 'uevent' sysfs attribute to trigger slot events

[Krzysztof Wilczyński]

Hello,

> > > +static struct pci_slot_attribute hotplug_slot_attr_uevent = {
> > > +	.attr = {.name = "uevent", .mode = S_IFREG | 0200},
> > > +	.show = NULL,
> > > +	.store = uevent_write_file
> > > +};
> > I think, you could use the __ATTR_WO() macro here.
> Use of the suggested macro is not appropriate

Just to expand on the "not appropriate" bit here.

Not wanting to change the name to have the _store suffix would be fine.

The __ATTR() would work here.  But, this file is old and wanting to
keep the style aligned with rest of it would be fine, too.

So, both of these reasons would be fine, to avoid using any new macro.

Thank you!

	Krzysztof

Re: [PATCH v2 1/1] PCI/hotplug: Add 'uevent' sysfs attribute to trigger slot events

[Krzysztof Wilczyński]

Hello,

> > > > > +static struct pci_slot_attribute hotplug_slot_attr_uevent = {
> > > > > +	.attr = {.name = "uevent", .mode = S_IFREG | 0200},
> > > > > +	.show = NULL,
> > > > > +	.store = uevent_write_file
> > > > > +};
> > > > I think, you could use the __ATTR_WO() macro here.
> > > Use of the suggested macro is not appropriate
> > Just to expand on the "not appropriate" bit here.
> > 
> > Not wanting to change the name to have the _store suffix would be fine.
> > 
> > The __ATTR() would work here.  But, this file is old and wanting to
> > keep the style aligned with rest of it would be fine, too.
> > 
> > So, both of these reasons would be fine, to avoid using any new macro.
[...]
> 
> Hello Krzysztof, let me first apologize to you in the way I said it. I
> should have elaborated the reasoning the way you did. I am open to making
> the changing if anyone else feels it is a better way.

Oh, no worries.  No hard feelings. :)

I just wanted to add a little bit more details for posterity. 

Thank you!

	Krzysztof