linux-kernel - [Patch 1/2] Driver core: Clarify device cleanup.

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Message-ID: <20080903182640.14279526@gondolin.boeblingen.de.ibm.com>
Date:	Wed, 3 Sep 2008 18:26:40 +0200
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	Greg K-H <greg@...ah.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [Patch 1/2] Driver core: Clarify device cleanup.

Make the comments on how to use device_initialize(), device_add()
and device_register() a bit clearer - in particular, explicitly
note that put_device() must be used once we tried to add the device
to the hierarchy.

Signed-off-by: Cornelia Huck <cornelia.huck@...ibm.com>

---
 drivers/base/core.c |   23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

Index: linux-2.6/drivers/base/core.c
===================================================================
--- linux-2.6.orig/drivers/base/core.c
+++ linux-2.6/drivers/base/core.c
@@ -524,11 +524,16 @@ static void klist_children_put(struct kl
  * device_initialize - init device structure.
  * @dev: device.
  *
- * This prepares the device for use by other layers,
- * including adding it to the device hierarchy.
+ * This prepares the device for use by other layers by initializing
+ * its fields.
  * It is the first half of device_register(), if called by
- * that, though it can also be called separately, so one
- * may use @dev's fields (e.g. the refcount).
+ * that function, though it can also be called separately, so one
+ * may use @dev's fields. In particular, get_device()/put_device()
+ * may be used for reference counting of @dev after calling this
+ * function.
+ *
+ * NOTE: Use put_device() to give up your reference instead of freeing
+ * @dev directly once you have called this function.
  */
 void device_initialize(struct device *dev)
 {
@@ -836,9 +841,13 @@ static void device_remove_sys_dev_entry(
  * This is part 2 of device_register(), though may be called
  * separately _iff_ device_initialize() has been called separately.
  *
- * This adds it to the kobject hierarchy via kobject_add(), adds it
+ * This adds @dev to the kobject hierarchy via kobject_add(), adds it
  * to the global and sibling lists for the device, then
  * adds it to the other relevant subsystems of the driver model.
+ *
+ * NOTE: _Never_ directly free @dev after calling this function, even
+ * if it returned an error! Always use put_device() to give up your
+ * reference instead.
  */
 int device_add(struct device *dev)
 {
@@ -958,6 +967,10 @@ int device_add(struct device *dev)
  * I.e. you should only call the two helpers separately if
  * have a clearly defined need to use and refcount the device
  * before it is added to the hierarchy.
+ *
+ * NOTE: _Never_ directly free @dev after calling this function, even
+ * if it returned an error! Always use put_device() to give up the
+ * reference initialized in this function instead.
  */
 int device_register(struct device *dev)
 {
--
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