linux-kernel - [PATCH 1/2] driver core: emit uevents when device is bound to a driver

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Date:   Sun, 12 Feb 2017 16:36:18 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, Guenter Roeck <linux@...ck-us.net>
Subject: [PATCH 1/2] driver core: emit uevents when device is bound to a driver

Majority of standard for a subsystem device attributes are created at the
same time devices are created, before KOBJECT_ADD uevent is emitted by the
driver core. This means that attributes are there when userspace is
notified about new device appearance.

However many drivers create additional driver-specific device attributes
when binding to the device, to provide userspace with additional controls,
and such attributes may not be there yet when userpsace receives
KOBJECT_ADD event. Changing the drivers to introduce intermediate "dummy"
device as a container for such attributes would be wasteful, and in many
cases, braking our sysfs ABI. Let's add a new event, KOBJECT_BIND (and its
counterpart, KOBJECT_UNBIND) that is emitted after a driver is bound to a
device. It can be used by userspace wishing to use driver-specific
attributes of a device.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
---
 drivers/base/dd.c       | 4 ++++
 include/linux/kobject.h | 2 ++
 lib/kobject_uevent.c    | 2 ++
 3 files changed, 8 insertions(+)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index a1fbf55c4d3a..a9a5cc0560e5 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -258,6 +258,8 @@ static void driver_bound(struct device *dev)
 	if (dev->bus)
 		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
 					     BUS_NOTIFY_BOUND_DRIVER, dev);
+
+	kobject_uevent(&dev->kobj, KOBJ_BIND);
 }

 static int driver_sysfs_add(struct device *dev)
@@ -839,6 +841,8 @@ static void __device_release_driver(struct device *dev, struct device *parent)
 			blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
 						     BUS_NOTIFY_UNBOUND_DRIVER,
 						     dev);
+
+		kobject_uevent(&dev->kobj, KOBJ_UNBIND);
 	}
 }

diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index e6284591599e..07292df4776e 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -57,6 +57,8 @@ enum kobject_action {
 	KOBJ_MOVE,
 	KOBJ_ONLINE,
 	KOBJ_OFFLINE,
+	KOBJ_BIND,
+	KOBJ_UNBIND,
 	KOBJ_MAX
 };

diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index 9a2b811966eb..4682e8545b5c 100644
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -50,6 +50,8 @@ static const char *kobject_actions[] = {
 	[KOBJ_MOVE] =		"move",
 	[KOBJ_ONLINE] =		"online",
 	[KOBJ_OFFLINE] =	"offline",
+	[KOBJ_BIND] =		"bind",
+	[KOBJ_UNBIND] =		"unbind",
 };

 /**
-- 
2.11.0.483.g087da7b7c-goog