设备

Linux设备模型－－设备 2012-03-24 20:34:01

分类： LINUX

linux中每个设备由一个struct device描述：

struct device {
    struct klist        klist_children;
    struct klist_node   knode_parent;   /* node in sibling list */
    struct klist_node   knode_driver;
    struct klist_node   knode_bus;
    struct device       *parent;
    struct kobject kobj;
    char    bus_id[BUS_ID_SIZE];    /* 在总线上唯一标识该设备的字符串position on parent bus */
    unsigned        uevent_suppress:1;
    const char      *init_name; /* initial name of the device */
    struct device_type  *type;
    struct semaphore    sem;    /* semaphore to synchronize calls to
                     * its driver.
                     */
    struct bus_type *bus;       /*设备所在总线 type of bus device is on */
    struct device_driver *driver;   /* 管理该设备的驱动which driver has allocated this
                       device */
    void        *driver_data;   /* 该设备驱动使用的私有数据成员data private to the driver */
    void        *platform_data; /* Platform specific data, device
                       core doesn't touch it */
    struct dev_pm_info  power;
#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 */
    /* arch specific additions */
    struct dev_archdata archdata;
    dev_t           devt;   /* dev_t, creates the sysfs "dev" */
    spinlock_t      devres_lock;
    struct list_head    devres_head;
    struct klist_node   knode_class;
    struct class        *class;
    struct attribute_group  **groups;   /* optional groups */
    void    (*release)(struct device *dev);
};
struct device_private {
    struct klist klist_children;
    struct klist_node knode_parent;
    struct klist_node knode_driver;
    struct klist_node knode_bus;
    struct device *device;
};  
设备属性由device_attribute描述
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);
};

可以看出device结构体中也包含了一个kobject对象
注册一个设备
int device_register(struct device *dev)
删除一个设备
void  device_unregister(struct device *dev)

注意：一条总线本身也是一个设备，也必须按设备注册，见上篇Linux设备模型－－总线

创建属性

int device_create_file(struct device *dev,struct device_attribute *attr)

删除属性

int device_remove_file(struct device *dev,struct device_attribute *attr)

添加设备例子，添加到前面创建的my_bus总线上：

#include

#include

#include

#include

#include

MODULE_AUTHOR("David Xie");

MODULE_LICENSE("Dual BSD/GPL");

extern struct device my_bus; 

extern struct bus_type my_bus_type;

/* Why need this ?*/

static void my_dev_release(struct device *dev)

{ 

}

struct device my_dev = {

.bus = &my_bus_type,//设备所在总线

.parent = &my_bus,//设备父设备，这里就是my_bus总线

.release = my_dev_release,

};

/*

 * Export a simple attribute.

 */

static ssize_t mydev_show(struct device *dev, char *buf)

{

return sprintf(buf, "%s\n", "This is my device!");

}

static DEVICE_ATTR(dev, S_IRUGO, mydev_show, NULL);

static int __init my_device_init(void)

{

int ret = 0;

        

        /* 初始化设备 */

strncpy(my_dev.bus_id, "my_dev", BUS_ID_SIZE);

        

        /*注册设备*/

device_register(&my_dev);

/*创建属性文件*/

device_create_file(&my_dev, &dev_attr_dev);

return ret;

}

static void my_device_exit(void)

{

device_unregister(&my_dev);

}

module_init(my_device_init);

module_exit(my_device_exit);

注册一个bus_id即名字为my_dev的设备，该设备的bus成员指向上一步创建的my_bus_type总线，parent成员指向上一步创建的my_bus总线设备。

         测试结果：

运行程序：
ls /sys/bus/my_bus/device
my_dev