#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/slab.h>
static dev_t dev_nr;
static struct cdev my_cdev;
static struct class *my_class;
#define MEMSIZE 64
static int my_open(struct inode *inode, struct file *filp)
{
filp->private_data = kmalloc(MEMSIZE, GFP_KERNEL);
if (!filp->private_data) {
pr_err("hello_cdev - Out of memory\n");
return -ENOMEM;
}
return 0;
}
static int my_release(struct inode *inode, struct file *filp)
{
kfree(filp->private_data);
return 0;
}
static ssize_t my_read(struct file *filp, char __user *user_buf, size_t len, loff_t *off)
{
char *text = filp->private_data;
int not_copied, delta, to_copy = (len + *off) < MEMSIZE ? len : (MEMSIZE - *off);
pr_info("hello_cdev - Read is called, we want to read %ld bytes, but actually only copying %d bytes. The offset is %lld\n", len, to_copy, *off);
if (*off >= MEMSIZE)
return 0;
not_copied = copy_to_user(user_buf, &text[*off], to_copy);
delta = to_copy - not_copied;
if (not_copied)
pr_warn("hello_cdev - Could only copy %d bytes\n", delta);
*off += delta;
return delta;
}
static ssize_t my_write(struct file *filp, const char __user *user_buf, size_t len, loff_t *off)
{
char *text = filp->private_data;
int not_copied, delta, to_copy = (len + *off) < MEMSIZE ? len : (MEMSIZE - *off);
pr_info("hello_cdev - Write is called, we want to write %ld bytes, but actually only copying %d bytes. The offset is %lld\n", len, to_copy, *off);
if (*off >= MEMSIZE)
return 0;
not_copied = copy_from_user(&text[*off], user_buf, to_copy);
delta = to_copy - not_copied;
if (not_copied)
pr_warn("hello_cdev - Could only copy %d bytes\n", delta);
*off += delta;
return delta;
}
static struct file_operations fops = {
.read = my_read,
.write = my_write,
.open = my_open,
.release = my_release,
.llseek = default_llseek,
};
static int __init my_init(void)
{
int status;
#ifdef STATIC_DEVNR
dev_nr = STATIC_DEVNR;
status = register_chrdev_region(dev_nr, MINORMASK + 1, "hello_cdev");
#else
status = alloc_chrdev_region(&dev_nr, 0, MINORMASK + 1, "hello_cdev");
#endif
if (status) {
pr_err("hello_cdev - Error reserving the region of device numbers\n");
return status;
}
cdev_init(&my_cdev, &fops);
my_cdev.owner = THIS_MODULE;
status = cdev_add(&my_cdev, dev_nr, MINORMASK + 1);
if (status) {
pr_err("hello_cdev - Error adding cdev\n");
goto free_devnr;
}
pr_info("hello_cdev - Registered a character device for Major %d starting with Minor %d\n", MAJOR(dev_nr), MINOR(dev_nr));
my_class = class_create("my_class");
if (!my_class) {
pr_err("hello_cdev - Could not create class my_class\n");
status = ENOMEM;
goto delete_cdev;
}
if (!device_create(my_class, NULL, dev_nr, NULL, "hello%d", 0)) {
pr_err("hello_cdev - Could not create device hello0\n");
status = ENOMEM;
goto delete_class;
}
pr_info("hello_cdev - Created device under /sys/class/my_class/hello0\n");
return 0;
delete_class:
class_unregister(my_class);
class_destroy(my_class);
delete_cdev:
cdev_del(&my_cdev);
free_devnr:
unregister_chrdev_region(dev_nr, MINORMASK + 1);
return status;
}
static void __exit my_exit(void)
{
device_destroy(my_class, dev_nr);
class_unregister(my_class);
class_destroy(my_class);
cdev_del(&my_cdev);
unregister_chrdev_region(dev_nr, MINORMASK + 1);
}
module_init(my_init);
module_exit(my_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Johannes 4Linux");
MODULE_DESCRIPTION("A sample driver for manually registering a character device");和lesson10 auto_devfile 相对应的是其添加修改了open/release/read/write 。
malloc/free 在c 里面很常见的成对出现，用于申请内存空间和释放内存空间，这里的kmalloc/free 成对出现在open/release 里面。要实现这对就要在头文件添加<linux/slab.h>.参数
GFP_KERNEL：常规
GFP_ATOMIC：中断上下文调用，原子操作
GFP_DMA: DMA 申请一段连续空间。
程序只是学习使用，JOHANNES 就直接给GFP_KENREL。
然后read/write 函数里面就是copy_to_user()/user_to_copy()。
不看视频，直接看这个程序，能理解这个程序是注册了一个字符设备文件，打开字符设备文件就会申请下一段64字节(MEMSIZE)内存空间，从外部用户层给内存空间读写数据，就会对这段内存空间进行读写。
觉得没太多可说的。就是lesson8/lesson10 综合加上了一段内存空间申请读写。