[PATCH v5 0/1] PCI: hotplug: Add support for synthesizing slot uevents

[PATCH v5 0/1] PCI: hotplug: Add support for synthesizing slot uevents

[Ramesh Errabolu]

Hi all,

This patch adds support for synthesizing PCI hotplug slot uevents via a
sysfs attribute.

The patch has been rebased on top of the current upstream/devel branch
and includes the feedback received during previous review rounds. The
Reviewed-by and Tested-by tags from the previous revision have been
retained.

I'd appreciate feedback on the next steps in the review and merge
process. Please let me know if any further changes are needed.

Thanks,
Ramesh Errabolu

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 v5 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>
Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Tested-by: Niklas Schnelle <schnelle@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
@@ -173,12 +173,27 @@ static ssize_t presence_read_file(struct pci_slot *pci_slot, char *buf)
 
 static struct pci_slot_attribute hotplug_slot_attr_presence = {
 	.attr = {.name = "adapter", .mode = S_IFREG | S_IRUGO},
 	.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)
 {
 	struct hotplug_slot *slot = pci_slot->hotplug;
 	unsigned long ltest;
 	u32 test;
@@ -251,12 +266,17 @@ static int fs_add_slot(struct hotplug_slot *slot, struct pci_slot *pci_slot)
 		if (retval)
 			dev_err(&pci_slot->bus->dev,
 				"Error creating sysfs link (%d)\n", retval);
 		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);
 		if (retval)
 			goto exit_power;
 	}
@@ -303,19 +323,24 @@ static int fs_add_slot(struct hotplug_slot *slot, struct pci_slot *pci_slot)
 		sysfs_remove_file(&pci_slot->kobj,
 				  &hotplug_slot_attr_attention.attr);
 exit_attention:
 	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;
 }
 
 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);
 
 	if (has_attention_file(slot))
 		sysfs_remove_file(&pci_slot->kobj,
 				  &hotplug_slot_attr_attention.attr);
-- 
2.43.0

Re: [PATCH v5 1/1] PCI: hotplug: Add 'uevent' sysfs attribute to trigger slot events

[Niklas Schnelle]

On Mon, 2026-07-06 at 15:02 -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>
> Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
> Tested-by: Niklas Schnelle <schnelle@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
> @@ -173,12 +173,27 @@ static ssize_t presence_read_file(struct pci_slot *pci_slot, char *buf)
>  
>  static struct pci_slot_attribute hotplug_slot_attr_presence = {
>  	.attr = {.name = "adapter", .mode = S_IFREG | S_IRUGO},
>  	.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,

As Bjorn Helgaas noted on v4 this ".show = NULL" is unnecessary. This
feedback should have been incorporated. And without that change there
is, as far as I can tell, no change vs v4 so this should have been
"[PATCH RESEND]" which Bjorn also told you in the same mail.

Thanks,
Niklas

[0] https://lore.kernel.org/linux-pci/20260521144853.GA163149@bhelgaas/