ARM驱动学习之9注册字符类设备
• 分配内存空间函数kmalloc
– 分配连续的虚拟地址,用于小内存分配。在include/linux/slab.h文件中。
– 参数1:申请的内存大小(最大128K),
– 参数2:GFP_KERNEL,代表优先权,内存不够可以延迟分配
• 分配内存空间函数kmalloc
– 分配连续的虚拟地址,用于小内存分配。在include/linux/slab.h文件中。
– 参数1:申请的内存大小(最大128K),
– 参数2:GFP_KERNEL,代表优先权,内存不够可以延迟分配
• 字符设备初始化函数cdev_init
– 在头文件include/linux/cdev.h中
– 参数1:cdev字符设备文件结构体
– 参数2:file_operations结构体
– 注册设备本质是向linux设备文件中添加数据,这些数据需要初始化
/**
* cdev_init() - initialize a cdev structure
* @cdev: the structure to initialize
* @fops: the file_operations for this device
*
* Initializes @cdev, remembering @fops, making it ready to add to the
* system with cdev_add().
*/
void cdev_init(struct cdev *cdev, const struct file_operations *fops)
{
memset(cdev, 0, sizeof *cdev);
INIT_LIST_HEAD(&cdev->list);
kobject_init(&cdev->kobj, &ktype_cdev_default);
cdev->ops = fops;
}
• 字符设备注册函数cdev_add
– 在头文件include/linux/cdev.h中
– 参数1:cdev字符设备文件结构体
– 参数2:设备号
– 参数3:设备范围大小
– 向系统注册设备,也就是向linux系统添加数据
/**
* cdev_add() - add a char device to the system
* @p: the cdev structure for the device
* @dev: the first device number for which this device is responsible
* @count: the number of consecutive minor numbers corresponding to this
* device
*
* cdev_add() adds the device represented by @p to the system, making it
* live immediately. A negative error code is returned on failure.
*/
int cdev_add(struct cdev *p, dev_t dev, unsigned count)
{
p->dev = dev;
p->count = count;
return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p);
}
static void cdev_unmap(dev_t dev, unsigned count)
{
kobj_unmap(cdev_map, dev, count);
}
• 卸载设备函数cdev_del
– 参数1:cdev结构体
– 移除字符设备
/**
* cdev_del() - remove a cdev from the system
* @p: the cdev structure to be removed
*
* cdev_del() removes @p from the system, possibly freeing the structure
* itself.
*/
void cdev_del(struct cdev *p)
{
cdev_unmap(p->dev, p->count);
kobject_put(&p->kobj);
}
1.文件名和Makefile修改为register_cdev
头文件:
/*三个字符设备函数*/
#include <linux/stat.h>
/*MKDEV转换设备号数据类型的宏定义*/
#include <linux/kdev_t.h>
/*定义字符设备的结构体*/
#include <linux/cdev.h>
/*分配内存空间函数头文件*/
#include <linux/slab.h>
#define REGDEV_SIZE 3000
2.定义结构体:
struct reg_deg
{
char *data;
unsigned long size;
struct cdev cdev;
};
struct reg_dev *my_devices;
my_devices = kmalloc(DEVICE_MINOR_NUM * sizeof(struct reg_dev),GFP_KERNEL);
if(!my_devices){
ret = -ENOMEM;
goto fail;
}
memset(my_devices,0,DEVICE_MINOR_NUM * sizeof(struct reg_dev));//初始化缓存为0;
for(i = 0;i < DEVICE_MINOR_NUM;i ++){
my_devices[i].data = kmalloc(REGDEV_SIZE,GFP_KERNEL);
memset(&my_devices[i],0,REGDEV_SIZE);
}
fail:
unregister_chrdev_region(MDKEV(numdev_major,numdev_minor),DEVICE_MINOR_NUM);
printk(KERN_EMERG "kmalloc is fail\n");
return ret;