實現效果

在/sys/kernel/debug/目錄下創建一個ion/test文件，通過cat、echo的方式進行讀寫操作：

前期準備

內核配置打開debugfs：

CONFIG_DEBUG_FS=y

掛載debugfs文件系統：

mount -t debugfs none /sys/kernel/debug

代碼實現

讀寫變量：

#include < linux/debugfs.h >
#include < linux/module.h >
#include < linux/types.h >

static struct dentry *ion_dir;
static u64 test_u64 = 0;

static int __init debugfs_init(void)
{

    //創建一個/sys/kernel/debug/ion目錄
    ion_dir = debugfs_create_dir("ion", NULL);
    if (!ion_dir) {
        printk("ion_dir is nulln");
        return -1;
    }

    /* 創建/sys/kernel/debug/ion/test_u64文件 */
    debugfs_create_u64("test_u64", 0644,
                        ion_dir, &test_u64);

    return 0;
}

static void __exit debugfs_exit(void)
{
    debugfs_remove_recursive(ion_dir);
}

module_init(debugfs_init);
module_exit(debugfs_exit);
MODULE_LICENSE("GPL");

運行結果：

讀寫字符串：

#include < linux/debugfs.h >
#include < linux/module.h >
#include < linux/fs.h >
#include < linux/uaccess.h >
#include < linux/errno.h >
#include < linux/dcache.h >
#include < linux/types.h >

static char ion_buf[512] = "hellon";
static struct dentry *ion_dir;

static int ion_open(struct inode *inode, struct file *filp)
{
    //printk("ion openn");
    return 0;
}

ssize_t ion_read(struct file *filp, char __user *buf, size_t count, loff_t *offp)
{
    int retval = 0;
    if ((*offp + count) > 512)
        count = 512 - *offp;

    if (copy_to_user(buf, ion_buf+*offp, count)) {
        printk("copy to user failed, count:%ldn", count);
        retval = -EFAULT;
        goto out;
    }
    *offp += count;
    retval = count;
out:
    return retval;
}

ssize_t ion_write(struct file *filp, const char __user *buff, size_t count, loff_t *offp)
{
    int retval;

    if (*offp > 512)
        return 0;

    if (*offp + count > 512)
        count = 512 - *offp;

    if (copy_from_user(ion_buf+*offp, buff, count)) {
        printk("copy from user failed, count:%ldn", count);
        retval = -EFAULT;
        goto out;
    }
    *offp += count;
    retval = count;
out:
    return retval;
}

struct file_operations my_fops = {
    .owner = THIS_MODULE,
    .read = ion_read,
    .write = ion_write,
    .open = ion_open,
};

static int __init debugfs_init(void)
{
    printk("INIT MODULEn");

    //創建一個/sys/kernel/debug/ion目錄
    ion_dir = debugfs_create_dir("ion", NULL);
    if (!ion_dir) {
        printk("ion_dir is nulln");
        return -1;
    }

    /* 創建/sys/kernel/debug/ion/test文件 */
    struct dentry *filent = debugfs_create_file("test", 0644, ion_dir, NULL, &my_fops);
    if (!filent) {
        printk("test file is nulln");
        return -1;
    }

    return 0;
}

static void __exit debugfs_exit(void)
{
    debugfs_remove_recursive(ion_dir);
}

module_init(debugfs_init);
module_exit(debugfs_exit);
MODULE_LICENSE("GPL");

運行結果：