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+The Basic Device Structure
+See the kerneldoc for the struct device.
+Programming Interface
+The bus driver that discovers the device uses this to register the
+device with the core:
+int device_register(struct device * dev);
+The bus should initialize the following fields:
+ - parent
+ - name
+ - bus_id
+ - bus
+A device is removed from the core when its reference count goes to
+0. The reference count can be adjusted using:
+struct device * get_device(struct device * dev);
+void put_device(struct device * dev);
+get_device() will return a pointer to the struct device passed to it
+if the reference is not already 0 (if it's in the process of being
+removed already).
+A driver can access the lock in the device structure using:
+void lock_device(struct device * dev);
+void unlock_device(struct device * dev);
+struct device_attribute {
+ struct attribute attr;
+ ssize_t (*show)(struct device *dev, struct device_attribute *attr,
+ char *buf);
+ ssize_t (*store)(struct device *dev, struct device_attribute *attr,
+ const char *buf, size_t count);
+Attributes of devices can be exported by a device driver through sysfs.
+Please see Documentation/filesystems/sysfs.txt for more information
+on how sysfs works.
+As explained in Documentation/kobject.txt, device attributes must be be
+created before the KOBJ_ADD uevent is generated. The only way to realize
+that is by defining an attribute group.
+Attributes are declared using a macro called DEVICE_ATTR:
+#define DEVICE_ATTR(name,mode,show,store)
+static DEVICE_ATTR(type, 0444, show_type, NULL);
+static DEVICE_ATTR(power, 0644, show_power, store_power);
+This declares two structures of type struct device_attribute with respective
+names 'dev_attr_type' and 'dev_attr_power'. These two attributes can be
+organized as follows into a group:
+static struct attribute *dev_attrs[] = {
+ &dev_attr_type.attr,
+ &dev_attr_power.attr,
+static struct attribute_group dev_attr_group = {
+ .attrs = dev_attrs,
+static const struct attribute_group *dev_attr_groups[] = {
+ &dev_attr_group,
+This array of groups can then be associated with a device by setting the
+group pointer in struct device before device_register() is invoked:
+ dev->groups = dev_attr_groups;
+ device_register(dev);
+The device_register() function will use the 'groups' pointer to create the
+device attributes and the device_unregister() function will use this pointer
+to remove the device attributes.
+Word of warning: While the kernel allows device_create_file() and
+device_remove_file() to be called on a device at any time, userspace has
+strict expectations on when attributes get created. When a new device is
+registered in the kernel, a uevent is generated to notify userspace (like
+udev) that a new device is available. If attributes are added after the
+device is registered, then userspace won't get notified and userspace will
+not know about the new attributes.
+This is important for device driver that need to publish additional
+attributes for a device at driver probe time. If the device driver simply
+calls device_create_file() on the device structure passed to it, then
+userspace will never be notified of the new attributes.