On Mon, Jan 21, 2008 at 10:24:17PM -0800, David Brownell wrote:
quoted text
> On Monday 21 January 2008, Dave Young wrote:
> >  
> > +/**
> > + *	class_for_each_device - device iterator
> > + *	@class:	the class we're iterating
> > + *	@data: data for the callback
> > + *	@fn: function to be called for each device
> > + *
> > + *	Iterate over @class's list of devices, and call @fn for each,
> > + *	passing it @data.
> > + *
> > + *	We check the return of @fn each time. If it returns anything
> > + *	other than 0, we break out and return that value.
> 
> I have a suggestion for better documentation, which
> applies to all these utilities:
> 
> 
> > + */
> > +int class_for_each_device(struct class *class, void *data,
> > +			   int (*fn)(struct device *, void *))
> > +{
> > +	struct device *dev;
> > +	int error = 0;
> > +
> > +	if (!class)
> > +		return -EINVAL;
> > +	down(&class->sem);
> > +	list_for_each_entry(dev, &class->devices, node) {
> > +		dev = get_device(dev);
> > +		if (dev) {
> > +			error = fn(dev, data);
> 
> This is called with class->sem held.  So fn() has a
> constraint to not re-acquire that ... else it'd be
> self-deadlocking.  I'd like to see docs at least
> mention that; calls to add or remove class members
> would be verboten, for example, which isn't an issue
> with most other driver model iterators.
> 
> 
> > +			put_device(dev);
> > +		} else
> > +			error = -ENODEV;
> > +		if (error)
> > +			break;
> > +	}
> > +	up(&class->sem);
> > +
> > +	return error;
> > +}
> > +EXPORT_SYMBOL_GPL(class_for_each_device);

Update kerneldoc as david brownell's sugestion.
Is it right for me add Cornelia Huck's ack after this change?
---

Add the following class iteration functions for driver use:
class_for_each_device
class_find_device
class_for_each_child
class_find_child

Signed-off-by: Dave Young <hidave.darkstar@gmail.com> 
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>

---
 drivers/base/class.c   |  175 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/device.h |   11 ++-
 2 files changed, 184 insertions(+), 2 deletions(-)

diff -upr linux/drivers/base/class.c linux.new/drivers/base/class.c
--- linux/drivers/base/class.c	2008-01-22 15:06:55.000000000 +0800
+++ linux.new/drivers/base/class.c	2008-01-22 15:06:55.000000000 +0800
@@ -798,6 +798,181 @@ void class_device_put(struct class_devic
 		kobject_put(&class_dev->kobj);
 }
 
+/**
+ * class_for_each_device - device iterator
+ * @class: the class we're iterating
+ * @data: data for the callback
+ * @fn: function to be called for each device
+ *
+ * Iterate over @class's list of devices, and call @fn for each,
+ * passing it @data.
+ *
+ * We check the return of @fn each time. If it returns anything
+ * other than 0, we break out and return that value.
+ *
+ * Note, we hold class->sem in this function, so it can not be
+ * re-acquired in @fn, otherwise it will self-deadlocking. For
+ * example, calls to add or remove class members would be verboten.
+ */
+int class_for_each_device(struct class *class, void *data,
+			   int (*fn)(struct device *, void *))
+{
+	struct device *dev;
+	int error = 0;
+
+	if (!class)
+		return -EINVAL;
+	down(&class->sem);
+	list_for_each_entry(dev, &class->devices, node) {
+		dev = get_device(dev);
+		if (dev) {
+			error = fn(dev, data);
+			put_device(dev);
+		} else
+			error = -ENODEV;
+		if (error)
+			break;
+	}
+	up(&class->sem);
+
+	return error;
+}
+EXPORT_SYMBOL_GPL(class_for_each_device);
+
+/**
+ * class_find_device - device iterator for locating a particular device
+ * @class: the class we're iterating
+ * @data: data for the match function
+ * @match: function to check device
+ *
+ * This is similar to the class_for_each_dev() function above, but it
+ * returns a reference to a device that is 'found' for later use, as
+ * determined by the @match callback.
+ *
+ * The callback should return 0 if the device doesn't match and non-zero
+ * if it does.  If the callback returns non-zero, this function will
+ * return to the caller and not iterate over any more devices.
+
+ * Note, you will need to drop the reference with put_device() after use.
+ *
+ * We hold class->sem in this function, so it can not be
+ * re-acquired in @match, otherwise it will self-deadlocking. For
+ * example, calls to add or remove class members would be verboten.
+ */
+struct device *class_find_device(struct class *class, void *data,
+				   int (*match)(struct device *, void *))
+{
+	struct device *dev;
+	int found = 0;
+
+	if (!class)
+		return NULL;
+
+	down(&class->sem);
+	list_for_each_entry(dev, &class->devices, node) {
+		dev = get_device(dev);
+		if (dev) {
+			if (match(dev, data)) {
+				found = 1;
+				break;
+			} else
+				put_device(dev);
+		} else
+			break;
+	}
+	up(&class->sem);
+
+	return found ? dev : NULL;
+}
+EXPORT_SYMBOL_GPL(class_find_device);
+
+/**
+ * class_for_each_child - class child iterator
+ * @class: the class we're iterating
+ * @data: data for the callback
+ * @fn: function to be called for each child of the class
+ *
+ * Iterate over @class's list of children, and call @fn for each,
+ * passing it @data.
+ *
+ * We check the return of @fn each time. If it returns anything
+ * other than 0, we break out and return that value.
+ *
+ * Note, we hold class->sem in this function, so it can not be
+ * re-acquired in @fn, otherwise it will self-deadlocking. For
+ * example, calls to add or remove class members would be verboten.
+ */
+int class_for_each_child(struct class *class, void *data,
+			   int (*fn)(struct class_device *, void *))
+{
+	struct class_device *dev;
+	int error = 0;
+
+	if (!class)
+		return -EINVAL;
+	down(&class->sem);
+	list_for_each_entry(dev, &class->children, node) {
+		dev = class_device_get(dev);
+		if (dev) {
+			error = fn(dev, data);
+			class_device_put(dev);
+		} else
+			error = -ENODEV;
+		if (error)
+			break;
+	}
+	up(&class->sem);
+
+	return error;
+}
+EXPORT_SYMBOL_GPL(class_for_each_child);
+
+/**
+ * class_find_child - device iterator for locating a particular class_device
+ * @class: the class we're iterating
+ * @data: data for the match function
+ * @match: function to check class_device
+ *
+ * This is similar to the class_for_each_child() function above, but it
+ * returns a reference to a class_device that is 'found' for later use, as
+ * determined by the @match callback.
+ *
+ * The callback should return 0 if the class_device doesn't match and non-zero
+ * if it does.  If the callback returns non-zero, this function will
+ * return to the caller and not iterate over any more class_devices.
+ *
+ * Note, you will need to drop the reference with class_device_put() after use.
+ *
+ * We hold class->sem in this function, so it can not be
+ * re-acquired in @match, otherwise it will self-deadlocking. For
+ * example, calls to add or remove class members would be verboten.
+ */
+struct class_device *class_find_child(struct class *class, void *data,
+				   int (*match)(struct class_device *, void *))
+{
+	struct class_device *dev;
+	int found = 0;
+
+	if (!class)
+		return NULL;
+
+	down(&class->sem);
+	list_for_each_entry(dev, &class->children, node) {
+		dev = class_device_get(dev);
+		if (dev) {
+			if (match(dev, data)) {
+				found = 1;
+				break;
+			} else
+				class_device_put(dev);
+		} else
+			break;
+	}
+	up(&class->sem);
+
+	return found ? dev : NULL;
+}
+EXPORT_SYMBOL_GPL(class_find_child);
 
 int class_interface_register(struct class_interface *class_intf)
 {
diff -upr linux/include/linux/device.h linux.new/include/linux/device.h
--- linux/include/linux/device.h	2008-01-22 15:06:55.000000000 +0800
+++ linux.new/include/linux/device.h	2008-01-22 15:06:55.000000000 +0800
@@ -180,8 +180,7 @@ struct class {
 	struct list_head	devices;
 	struct list_head	interfaces;
 	struct kset		class_dirs;
-	struct semaphore	sem;	/* locks both the children and interfaces lists */
-
+	struct semaphore	sem; /* locks children, devices, interfaces */
 	struct class_attribute		* class_attrs;
 	struct class_device_attribute	* class_dev_attrs;
 	struct device_attribute		* dev_attrs;
@@ -199,6 +198,14 @@ struct class {
 
 extern int __must_check class_register(struct class *);
 extern void class_unregister(struct class *);
+extern int class_for_each_device(struct class *class, void *data,
+				int (*fn)(struct device *dev, void *data));
+extern struct device *class_find_device(struct class *class, void *data,
+				   int (*match)(struct device *, void *));
+extern int class_for_each_child(struct class *class, void *data,
+			   int (*fn)(struct class_device *, void *));
+extern struct class_device *class_find_child(struct class *class, void *data,
+				   int (*match)(struct class_device *, void *));
 
 
 struct class_attribute {
--
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