diff options
| -rw-r--r-- | Documentation/driver-model/device.txt | 65 |
1 files changed, 32 insertions, 33 deletions
diff --git a/Documentation/driver-model/device.txt b/Documentation/driver-model/device.txt index bdefe728a737..1e70220d20f4 100644 --- a/Documentation/driver-model/device.txt +++ b/Documentation/driver-model/device.txt @@ -45,33 +45,52 @@ struct device_attribute { const char *buf, size_t count); }; -Attributes of devices can be exported via drivers using a simple -procfs-like interface. +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) Example: -DEVICE_ATTR(power,0644,show_power,store_power); +static DEVICE_ATTR(type, 0444, show_type, NULL); +static DEVICE_ATTR(power, 0644, show_power, store_power); -This declares a structure of type struct device_attribute named -'dev_attr_power'. This can then be added and removed to the device's -directory using: +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: -int device_create_file(struct device *device, struct device_attribute * entry); -void device_remove_file(struct device * dev, struct device_attribute * attr); +static struct attribute *dev_attrs[] = { + &dev_attr_type.attr, + &dev_attr_power.attr, + NULL, +}; -Example: +static struct attribute_group dev_attr_group = { + .attrs = dev_attrs, +}; + +static const struct attribute_group *dev_attr_groups[] = { + &dev_attr_group, + NULL, +}; + +This array of groups can then be associated with a device by setting the +group pointer in struct device before device_register() is invoked: -device_create_file(dev,&dev_attr_power); -device_remove_file(dev,&dev_attr_power); + dev->groups = dev_attr_groups; + device_register(dev); -The file name will be 'power' with a mode of 0644 (-rw-r--r--). +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 @@ -84,24 +103,4 @@ 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. Instead, it should -probably use class_create() and class->dev_attrs to set up a list of -desired attributes in the modules_init function, and then in the .probe() -hook, and then use device_create() to create a new device as a child -of the probed device. The new device will generate a new uevent and -properly advertise the new attributes to userspace. - -For example, if a driver wanted to add the following attributes: -struct device_attribute mydriver_attribs[] = { - __ATTR(port_count, 0444, port_count_show), - __ATTR(serial_number, 0444, serial_number_show), - NULL -}; - -Then in the module init function is would do: - mydriver_class = class_create(THIS_MODULE, "my_attrs"); - mydriver_class.dev_attr = mydriver_attribs; - -And assuming 'dev' is the struct device passed into the probe hook, the driver -probe function would do something like: - device_create(&mydriver_class, dev, chrdev, &private_data, "my_name"); +userspace will never be notified of the new attributes. |