linux驱动模型中的 DEVICE_ATTR 宏分析

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定义于 "include/linux/device.h" 文件中：

#define DEVICE_ATTR(_name, _mode, _show, _store) \
struct device_attribute dev_attr_##_name = __ATTR(_name, _mode, _show, _store)

而 "kernel/include/linux/sysfs.h" 也定义了 __ATTR , 这个宏被多个设备模型的宏使用到了。

/**
* 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

sysfs.h 也定义了 struct attribute

/* FIXME
* The *owner field is no longer used.
* x86 tree has been cleaned up. The owner
* attribute is still left for other arches.
*/
struct attribute {
        const char              *name;
        struct module           *owner;
        mode_t                  mode;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
        struct lock_class_key   *key;
        struct lock_class_key   skey;
#endif
};

struct device_attribute 也定义于 "include/linux/device.h" 文件中：

/* 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);
};

所以， DEVICE_ATTR 这个宏实际上是定义并初始化了一个名叫 “dev_attr_##_name”的 struct device_attribute 类型的结构体。

关于mode_t这个类型

include/linux/types.h:

typedef __kernel_mode_t mode_t;

arch/arm/include/asm/posix_types.h

typedef unsigned short __kernel_mode_t;

实际上 mode_t 这个类型，就是 unsigned short

include/asm-generic/posix_types.h

typedef unsigned int __kernel_mode_t; // 因为我们的平台是arm架构的所以，用的应该是“arch/arm/include/asm/posix_types.h” 这个文件对__kernel_mode_t的定义。

include/asm-generic/types.h

typedef unsigned short umode_t;

arch/arm/include/asm/types.h

typedef unsigned short umode_t;