[PATCH v4] PCI: hotplug: Add 'uevent' sysfs attribute to trigger slot events

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

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