前言
如果你正在開發的設備驅動程序中需要與用戶層的接口，一般可選的方法有：
(1)、註冊虛擬的字符設備文件，以這個虛擬設備上的 read/write/ioctl 等接口與用戶交互；但 read/write 一般只能做一件事情， ioctl 可以根據 cmd 參數做多個功能，但其缺點是很明顯的： ioctl 接口無法直接在 Shell 腳本中使用，爲了使用 ioctl 的功能，還必須編寫配套的 C語言的虛擬設備操作程序， ioctl 的二進制數據接口也是造成大小端問題 (big endian與little endian)、32位/64位不可移植問題的根源；
(2)、 註冊 proc 接口，接受用戶的 read/write/ioctl 操作；同樣的，一個 proc 項通常使用其 read/write/ioctl 接口，它所存在的問題與上面的虛擬字符設備的的問題相似；
(3)、註冊 sysfs 屬性；
最重要的是，添加虛擬字符設備支持和註冊 proc 接口支持這兩者所需要增加的代碼量都並不少，最好的方法還是使用 sysfs 屬性支持，一切在用戶層是可見的透明，且增加的代碼量是最少的，可維護性也最好；方法就是使用 <include/linux/device.h> 頭文件提供的四個宏，分別應用於總線/類別/驅動/設備四種內核數據結構對象上。
#define BUS_ATTR(_name, _mode, _show, _store)
struct bus_attribute bus_attr_##_name = __ATTR(_name, _mode, _show, _store)
#define CLASS_ATTR(_name, _mode, _show, _store)
struct class_attribute class_attr_##_name = __ATTR(_name, _mode, _show, _store)
#define DRIVER_ATTR(_name, _mode, _show, _store)
struct driver_attribute driver_attr_##_name =
__ATTR(_name, _mode, _show, _store)
#define DEVICE_ATTR(_name, _mode, _show, _store)
struct device_attribute dev_attr_##_name = __ATTR(_name, _mode, _show, _store)
struct attribute {
const char *name;
umode_t mode;
};
struct attribute_group {
const char *name;
umode_t (*is_visible)(struct kobject *,
struct attribute *, int);
struct attribute **attrs;
};
/**
* Use these macros to make defining attributes easier. See include/linux/device.h
* for examples..
*/
#define __ATTR(_name,_mode,_show,_store) { \
.attr = {.name = __stringify(_name), .mode = _mode }, \
.show = _show, \
.store = _store, \
}
#define __ATTR_RO(_name) { \
.attr = { .name = __stringify(_name), .mode = 0444 }, \
.show = _name##_show, \
}
#define __ATTR_NULL { .attr = { .name = NULL } }
#define attr_name(_attr) (_attr).attr.name四種屬性接口
其實常用的就是DEVICE_ATTR，而DRIVER_ATTR用的也不多，另外2個BUS_ATTR和CLASS_ATTR基本不用，是定義好的框架或子系統，作爲驅動開發我們一般不會去建立新的框架或系統，在其上開發就行了，比如我們開發input子系統，你開發的屬性、設備基本都在/sys/xxx/input/下。
1、DEVICE_ATTR
屬性：
/* interface for exporting device attributes */
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);
};聲明：
DEVICE_ATTR(_name, _mode, _show, _store)創建：
/**
* device_create_file - create sysfs attribute file for device.
* @dev: device.
* @attr: device attribute descriptor.
*/
int device_create_file(struct device *dev,
const struct device_attribute *attr)
{
int error = 0;
if (dev)
error = sysfs_create_file(&dev->kobj, &attr->attr);
return error;
}釋放
/**
* device_remove_file - remove sysfs attribute file.
* @dev: device.
* @attr: device attribute descriptor.
*/
void device_remove_file(struct device *dev,
const struct device_attribute *attr)
{
if (dev)
sysfs_remove_file(&dev->kobj, &attr->attr);
}2、DRIVER_ATTR
屬性<span style="font-size:18px;">/* sysfs interface for exporting driver attributes */
struct driver_attribute {
struct attribute attr;
ssize_t (*show)(struct device_driver *driver, char *buf);
ssize_t (*store)(struct device_driver *driver, const char *buf,
size_t count);
};</span>聲明
DRIVER_ATTR(_name, _mode, _show, _store) 創建
/**
* driver_create_file - create sysfs file for driver.
* @drv: driver.
* @attr: driver attribute descriptor.
*/
int driver_create_file(struct device_driver *drv,
const struct driver_attribute *attr)
{
int error;
if (drv)
error = sysfs_create_file(&drv->p->kobj, &attr->attr);
else
error = -EINVAL;
return error;
}釋放
/**
* driver_remove_file - remove sysfs file for driver.
* @drv: driver.
* @attr: driver attribute descriptor.
*/
void driver_remove_file(struct device_driver *drv,
const struct driver_attribute *attr)
{
if (drv)
sysfs_remove_file(&drv->p->kobj, &attr->attr);
}3、BUS_ATTR
屬性struct bus_attribute {
struct attribute attr;
ssize_t (*show)(struct bus_type *bus, char *buf);
ssize_t (*store)(struct bus_type *bus, const char *buf, size_t count);
};聲明
BUS_ATTR(_name, _mode, _show, _store)int bus_create_file(struct bus_type *bus, struct bus_attribute *attr)
{
int error;
if (bus_get(bus)) {
error = sysfs_create_file(&bus->p->subsys.kobj, &attr->attr);
bus_put(bus);
} else
error = -EINVAL;
return error;
}釋放
void bus_remove_file(struct bus_type *bus, struct bus_attribute *attr)
{
if (bus_get(bus)) {
sysfs_remove_file(&bus->p->subsys.kobj, &attr->attr);
bus_put(bus);
}
}4、CLASS_ATTR
屬性struct class_attribute {
struct attribute attr;
ssize_t (*show)(struct class *class, struct class_attribute *attr,
char *buf);
ssize_t (*store)(struct class *class, struct class_attribute *attr,
const char *buf, size_t count);
const void *(*namespace)(struct class *class,
const struct class_attribute *attr);
};聲明
CLASS_ATTR(_name, _mode, _show, _store)創建
int class_create_file(struct class *cls, const struct class_attribute *attr)
{
int error;
if (cls)
error = sysfs_create_file(&cls->p->subsys.kobj,
&attr->attr);
else
error = -EINVAL;
return error;
}void class_remove_file(struct class *cls, const struct class_attribute *attr)
{
if (cls)
sysfs_remove_file(&cls->p->subsys.kobj, &attr->attr);
}設備驅動基本數據結構
懶得去翻閱/linux/device.h,貼一些常用的數據結構
1. struct device
<span style="font-size:14px;">/**
* struct device - The basic device structure
* @parent: The device's "parent" device, the device to which it is attached.
* In most cases, a parent device is some sort of bus or host
* controller. If parent is NULL, the device, is a top-level device,
* which is not usually what you want.
* @p: Holds the private data of the driver core portions of the device.
* See the comment of the struct device_private for detail.
* @kobj: A top-level, abstract class from which other classes are derived.
* @init_name: Initial name of the device.
* @type: The type of device.
* This identifies the device type and carries type-specific
* information.
* @mutex: Mutex to synchronize calls to its driver.
* @bus: Type of bus device is on.
* @driver: Which driver has allocated this
* @platform_data: Platform data specific to the device.
* Example: For devices on custom boards, as typical of embedded
* and SOC based hardware, Linux often uses platform_data to point
* to board-specific structures describing devices and how they
* are wired. That can include what ports are available, chip
* variants, which GPIO pins act in what additional roles, and so
* on. This shrinks the "Board Support Packages" (BSPs) and
* minimizes board-specific #ifdefs in drivers.
* @power: For device power management.
* See Documentation/power/devices.txt for details.
* @pm_domain: Provide callbacks that are executed during system suspend,
* hibernation, system resume and during runtime PM transitions
* along with subsystem-level and driver-level callbacks.
* @pins: For device pin management.
* See Documentation/pinctrl.txt for details.
* @numa_node: NUMA node this device is close to.
* @dma_mask: Dma mask (if dma'ble device).
* @coherent_dma_mask: Like dma_mask, but for alloc_coherent mapping as not all
* hardware supports 64-bit addresses for consistent allocations
* such descriptors.
* @dma_parms: A low level driver may set these to teach IOMMU code about
* segment limitations.
* @dma_pools: Dma pools (if dma'ble device).
* @dma_mem: Internal for coherent mem override.
* @archdata: For arch-specific additions.
* @of_node: Associated device tree node.
* @devt: For creating the sysfs "dev".
* @id: device instance
* @devres_lock: Spinlock to protect the resource of the device.
* @devres_head: The resources list of the device.
* @knode_class: The node used to add the device to the class list.
* @class: The class of the device.
* @groups: Optional attribute groups.
* @release: Callback to free the device after all references have
* gone away. This should be set by the allocator of the
* device (i.e. the bus driver that discovered the device).
*
* At the lowest level, every device in a Linux system is represented by an
* instance of struct device. The device structure contains the information
* that the device model core needs to model the system. Most subsystems,
* however, track additional information about the devices they host. As a
* result, it is rare for devices to be represented by bare device structures;
* instead, that structure, like kobject structures, is usually embedded within
* a higher-level representation of the device.
*/
struct device {
struct device *parent;
struct device_private *p;
struct kobject kobj;
const char *init_name; /* initial name of the device */
const struct device_type *type;
struct mutex mutex; /* mutex to synchronize calls to
* its driver.
*/
struct bus_type *bus; /* type of bus device is on */
struct device_driver *driver; /* which driver has allocated this
device */
void *platform_data; /* Platform specific data, device
core doesn't touch it */
struct dev_pm_info power;
struct dev_pm_domain *pm_domain;
#ifdef CONFIG_PINCTRL
struct dev_pin_info *pins;
#endif
#ifdef CONFIG_NUMA
int numa_node; /* NUMA node this device is close to */
#endif
u64 *dma_mask; /* dma mask (if dma'able device) */
u64 coherent_dma_mask;/* Like dma_mask, but for
alloc_coherent mappings as
not all hardware supports
64 bit addresses for consistent
allocations such descriptors. */
struct device_dma_parameters *dma_parms;
struct list_head dma_pools; /* dma pools (if dma'ble) */
struct dma_coherent_mem *dma_mem; /* internal for coherent mem
override */
#ifdef CONFIG_CMA
struct cma *cma_area; /* contiguous memory area for dma
allocations */
#endif
/* arch specific additions */
struct dev_archdata archdata;
struct device_node *of_node; /* associated device tree node */
dev_t devt; /* dev_t, creates the sysfs "dev" */
u32 id; /* device instance */
spinlock_t devres_lock;
struct list_head devres_head;
struct klist_node knode_class;
struct class *class;
const struct attribute_group **groups; /* optional groups */
void (*release)(struct device *dev);
struct iommu_group *iommu_group;
};</span>2. struct device_driver
<span style="font-size:14px;">/**
* struct device_driver - The basic device driver structure
* @name: Name of the device driver.
* @bus: The bus which the device of this driver belongs to.
* @owner: The module owner.
* @mod_name: Used for built-in modules.
* @suppress_bind_attrs: Disables bind/unbind via sysfs.
* @of_match_table: The open firmware table.
* @probe: Called to query the existence of a specific device,
* whether this driver can work with it, and bind the driver
* to a specific device.
* @remove: Called when the device is removed from the system to
* unbind a device from this driver.
* @shutdown: Called at shut-down time to quiesce the device.
* @suspend: Called to put the device to sleep mode. Usually to a
* low power state.
* @resume: Called to bring a device from sleep mode.
* @groups: Default attributes that get created by the driver core
* automatically.
* @pm: Power management operations of the device which matched
* this driver.
* @p: Driver core's private data, no one other than the driver
* core can touch this.
*
* The device driver-model tracks all of the drivers known to the system.
* The main reason for this tracking is to enable the driver core to match
* up drivers with new devices. Once drivers are known objects within the
* system, however, a number of other things become possible. Device drivers
* can export information and configuration variables that are independent
* of any specific device.
*/
struct device_driver {
const char *name;
struct bus_type *bus;
struct module *owner;
const char *mod_name; /* used for built-in modules */
bool suppress_bind_attrs; /* disables bind/unbind via sysfs */
const struct of_device_id *of_match_table;
int (*probe) (struct device *dev);
int (*remove) (struct device *dev);
void (*shutdown) (struct device *dev);
int (*suspend) (struct device *dev, pm_message_t state);
int (*resume) (struct device *dev);
const struct attribute_group **groups;
const struct dev_pm_ops *pm;
struct driver_private *p;
};</span>struct driver_private
挖你隱私，呵呵!這就是驅動對應的sysfs下的某個driver目錄，說白了driver_create_file()就是在其driver目錄下建attr
struct driver_private {
struct kobject kobj;
st<span style="font-size:12px;">ruct klist klist_devices;
struct klist_node</span> knode_bus;
struct module_kobject *mkobj;
struct device_driver *driver;
};3. struct bus_type
<span style="font-size:14px;">/**
* struct bus_type - The bus type of the device
*
* @name: The name of the bus.
* @dev_name: Used for subsystems to enumerate devices like ("foo%u", dev->id).
* @dev_root: Default device to use as the parent.
* @bus_attrs: Default attributes of the bus.
* @dev_attrs: Default attributes of the devices on the bus.
* @drv_attrs: Default attributes of the device drivers on the bus.
* @match: Called, perhaps multiple times, whenever a new device or driver
* is added for this bus. It should return a nonzero value if the
* given device can be handled by the given driver.
* @uevent: Called when a device is added, removed, or a few other things
* that generate uevents to add the environment variables.
* @probe: Called when a new device or driver add to this bus, and callback
* the specific driver's probe to initial the matched device.
* @remove: Called when a device removed from this bus.
* @shutdown: Called at shut-down time to quiesce the device.
* @suspend: Called when a device on this bus wants to go to sleep mode.
* @resume: Called to bring a device on this bus out of sleep mode.
* @pm: Power management operations of this bus, callback the specific
* device driver's pm-ops.
* @iommu_ops: IOMMU specific operations for this bus, used to attach IOMMU
* driver implementations to a bus and allow the driver to do
* bus-specific setup
* @p: The private data of the driver core, only the driver core can
* touch this.
*
* A bus is a channel between the processor and one or more devices. For the
* purposes of the device model, all devices are connected via a bus, even if
* it is an internal, virtual, "platform" bus. Buses can plug into each other.
* A USB controller is usually a PCI device, for example. The device model
* represents the actual connections between buses and the devices they control.
* A bus is represented by the bus_type structure. It contains the name, the
* default attributes, the bus' methods, PM operations, and the driver core's
* private data.
*/
struct bus_type {
const char *name;
const char *dev_name;
struct device *dev_root;
struct bus_attribute *bus_attrs;
struct device_attribute *dev_attrs;
struct driver_attribute *drv_attrs;
int (*match)(struct device *dev, struct device_driver *drv);
int (*uevent)(struct device *dev, struct kobj_uevent_env *env);
int (*probe)(struct device *dev);
int (*remove)(struct device *dev);
void (*shutdown)(struct device *dev);
int (*suspend)(struct device *dev, pm_message_t state);
int (*resume)(struct device *dev);
const struct dev_pm_ops *pm;
struct iommu_ops *iommu_ops;
struct subsys_private *p;
};</span>4. struct class
<span style="font-size:14px;">/**
* struct class - device classes
* @name: Name of the class.
* @owner: The module owner.
* @class_attrs: Default attributes of this class.
* @dev_attrs: Default attributes of the devices belong to the class.
* @dev_bin_attrs: Default binary attributes of the devices belong to the class.
* @dev_kobj: The kobject that represents this class and links it into the hierarchy.
* @dev_uevent: Called when a device is added, removed from this class, or a
* few other things that generate uevents to add the environment
* variables.
* @devnode: Callback to provide the devtmpfs.
* @class_release: Called to release this class.
* @dev_release: Called to release the device.
* @suspend: Used to put the device to sleep mode, usually to a low power
* state.
* @resume: Used to bring the device from the sleep mode.
* @ns_type: Callbacks so sysfs can detemine namespaces.
* @namespace: Namespace of the device belongs to this class.
* @pm: The default device power management operations of this class.
* @p: The private data of the driver core, no one other than the
* driver core can touch this.
*
* A class is a higher-level view of a device that abstracts out low-level
* implementation details. Drivers may see a SCSI disk or an ATA disk, but,
* at the class level, they are all simply disks. Classes allow user space
* to work with devices based on what they do, rather than how they are
* connected or how they work.
*/
struct class {
const char *name;
struct module *owner;
struct class_attribute *class_attrs;
struct device_attribute *dev_attrs;
struct bin_attribute *dev_bin_attrs;
struct kobject *dev_kobj;
int (*dev_uevent)(struct device *dev, struct kobj_uevent_env *env);
char *(*devnode)(struct device *dev, umode_t *mode);
void (*class_release)(struct class *class);
void (*dev_release)(struct device *dev);
int (*suspend)(struct device *dev, pm_message_t state);
int (*resume)(struct device *dev);
const struct kobj_ns_type_operations *ns_type;
const void *(*namespace)(struct device *dev);
const struct dev_pm_ops *pm;
struct subsys_private *p;
};
struct class_dev_iter {
struct klist_iter ki;
const struct device_type *type;
};</span>4.1 struct subsys_private
device,device_driver,bus_type,class都有一個私有成員p，這都是各自私有的，並且其用途由各自框架決定。前2個不討論，驅動人員經常碰到，後面2個都是用subsys_provate，貼下來，這要與bus_attr和class_attr的創建對比起來看。
<span style="font-size:14px;"> /*** struct subsys_private - structure to hold the private to the driver core portions of the bus_type/class structure.
*
* @subsys - the struct kset that defines this subsystem
* @devices_kset - the subsystem's 'devices' directory
* @interfaces - list of subsystem interfaces associated
* @mutex - protect the devices, and interfaces lists.
*
* @drivers_kset - the list of drivers associated
* @klist_devices - the klist to iterate over the @devices_kset
* @klist_drivers - the klist to iterate over the @drivers_kset
* @bus_notifier - the bus notifier list for anything that cares about things
* on this bus.
* @bus - pointer back to the struct bus_type that this structure is associated
* with.
*
* @glue_dirs - "glue" directory to put in-between the parent device to
* avoid namespace conflicts
* @class - pointer back to the struct class that this structure is associated
* with.
*
* This structure is the one that is the actual kobject allowing struct
* bus_type/class to be statically allocated safely. Nothing outside of the
* driver core should ever touch these fields.
*/
struct subsys_private {
struct kset subsys;
struct kset *devices_kset;
struct list_head interfaces;
struct mutex mutex;
struct kset *drivers_kset;
struct klist klist_devices;
struct klist klist_drivers;
struct blocking_notifier_head bus_notifier;
unsigned int drivers_autoprobe:1;
struct bus_type *bus;
struct kset glue_dirs;
struct class *class;
};</span>