写长到linux设备驱动？

Question

我试图在linux中编写一个字符设备驱动程序。不幸的是，它不适用于任何大于255的数字。

我希望这个驱动程序专门使用long类型的值。每当我输入大于255的值时，数字就错了。256到0等。

我编写了一个简单的字符设备驱动程序，显示了这个问题，当我复制完整的驱动程序并删除几乎所有内容时，可能会有很多未使用的include语句：

chartest.c

#include <linux/init.h>
#include <linux/module.h> /* I mean this is a module after all! */
#include <linux/moduleparam.h>
#include <linux/kernel.h>
#include <linux/sched.h> /* For current task information */
#include <linux/fs.h> /* For file operations */
#include <linux/types.h> /* dev_t: device number data type */
#include <linux/cdev.h> /* cdev is the module data type that the kernel sees */
#include <asm/uaccess.h> /* For routines to copy data to/from user space */
#include <linux/uaccess.h>
#include <linux/slab.h> /* kmalloc/kfree */


MODULE_LICENSE("GPL");

#define DRIVER_NAME "chartest"

#define MAJOR_NUM 230
#define MINOR_NUM 0

struct cdev *cdev;

int test_device_open(struct inode *inode, struct file *fp) {
    return 0;
}


int test_device_release(struct inode *inode, struct file *fp) {
    return 0;
}


ssize_t test_read(struct file *fp, char __user *buffer, size_t count, loff_t *f_pos) {
    return count;
}

ssize_t test_write(struct file *fp, const char __user *buffer, size_t count, loff_t *fpos) {
    // We must validate the user's buffer and convert it to a long long
    long userOperand;
    unsigned char *userInput = NULL;

    printk(KERN_NOTICE "Write Function Entered.\n");
    printk(KERN_ALERT "Write count: %ld, Write fp: %lld\n", count, *fpos);

    userInput = kmalloc(count, GFP_KERNEL); 
    get_user(*userInput, buffer);

    printk(KERN_NOTICE "Value before cast: %ld\n", (long) *userInput);

    userOperand = (long) *userInput;

    printk(KERN_NOTICE "Value after cast: %ld\n", userOperand);

    // Increment the file position pointer (in our case, always by 8)
    *fpos += count;

    kfree(userInput);
    return count;
}


/*
* Declaration of function for open file operations
*/
static struct file_operations test_fops = {
    .owner = THIS_MODULE,
    .read = test_read,
    .write = test_write,
    .open = test_device_open,
    .release = test_device_release,
};



// Initialization function
static int __init test_init(void)
{
    // Register device number:
    int err = 0;
    dev_t device_number = MKDEV(MAJOR_NUM, MINOR_NUM);

    err = register_chrdev_region(device_number, 1, DRIVER_NAME);

    if (err < 0) {
        printk(KERN_ALERT "Could not allocate device number.\n");
        return err;
    }

    cdev = cdev_alloc();
    cdev->owner = THIS_MODULE;
    cdev->ops = &test_fops;

    err = cdev_add(cdev, device_number, 1);
    if (err) {
        printk("Error allocating cdev.\n");
    }

    printk(KERN_ALERT "Test Initialized. Major Number: %d\n", MAJOR_NUM);

    return 0;
}

// Exit function:
static void __exit test_exit(void)
{
    dev_t device_number = MKDEV(MAJOR_NUM, MINOR_NUM);

    // Remove char device */
    cdev_del(cdev);

    /* Unregister Device Number: */
    unregister_chrdev_region(device_number, 1);
    printk(KERN_ALERT "TestDriver %d destroyed.\n", MAJOR_NUM);
}

module_init(test_init);
module_exit(test_exit);

小测试程序：

C.

#include <unistd.h>
#include <fcntl.h>



int main(void) {
    long input = 256;


    int fd = open("/dev/chartest0", O_RDWR);

    write(fd, &input, sizeof(long));

    close(fd);

    return 0;

}

printk语句提供以下输出，给定输入为256：

Write Eunction Entered.
Write count: 8, Write fp: 0
Value before cast: 0
Value after cast: 0

如果copy_from_user的输入放置大小为8字节，这也会失败。当每次迭代一个字节并复制数据时，它也会失败。我什么都试过了。

如果您非常乐意提供帮助，请使用: MakeFile编译

ifeq ($(KERNELRELEASE),)

    # Assume the source tree is where the running kernel was built
    # You should set KERNELDIR in the environment if it's elsewhere
    KERNELDIR ?= /lib/modules/$(shell uname -r)/build
    # The current directory is passed to sub-makes as argument
    PWD := $(shell pwd)

modules:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules

modules_install:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules_install

clean:
    rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions

.PHONY: modules modules_install clean

else
    # called from kernel build system: just declare what our modules are
    obj-m := chartest.o

endif

然后在同一个目录中：

sudo insmod chartest.ko

最后：

sudo mknod -m 777 /dev/chartest0 c 230 0

然后您可以编译maindriver.c并运行它来测试。

有人能帮我解决这个问题吗？

Answer 1

您不能以这样的方式使用get_user：

来自用户文档

此宏将单个简单变量从用户空间复制到内核空间。它支持char和int这样的简单类型，但是不支持更大的数据类型，比如结构或数组。 ptr必须具有指向简单变量类型的指针，并且取消引用ptr的结果必须在没有强制转换的情况下分配给x。

使用get_user，您将只复制第一个字符。

您需要使用copy_from_user，这个函数可以复制数组和结构，而不仅仅是简单的类型：

ssize_t test_write(struct file *fp, const char __user *buffer, size_t count, loff_t *fpos) {
    // We must validate the user's buffer and convert it to a long long
    long userOperand;
    unsigned char *userInput = NULL;

    userInput = kmalloc(count, GFP_KERNEL); 

    printk(KERN_NOTICE "Write Function Entered.\n");
    printk(KERN_ALERT "Write count: %ld, Write fp: %lld\n", count, *fpos);

    /* warning, here you should test that count is exactly sizeof userInput */
    copy_from_user(userInput, buffer, count);

    userOperand =  *(long*)userInput;

    printk(KERN_NOTICE "Value after cast: %ld\n", userOperand);

    // Increment the file position pointer (in our case, always by 8)
    *fpos += count;

    kfree(userInput);
    return count;
}

您还可以从char *复制到copy_from_user中的long (在这种情况下没有内存分配)：

ssize_t test_write(struct file *fp, const char __user *buffer, size_t count, loff_t *fpos) {
    // We must validate the user's buffer and convert it to a long long
    long userOperand;

    printk(KERN_NOTICE "Write Function Entered.\n");
    printk(KERN_ALERT "Write count: %ld, Write fp: %lld\n", count, *fpos);

    /* warning, here you should test that count is exactly sizeof userOperand */
    copy_from_user(&userOperand, buffer, sizeof userOperand);

    printk(KERN_NOTICE "Value after reading: %ld\n", userOperand);

    // Increment the file position pointer (in our case, always by 8)
    *fpos += count;

    return count;
}

Answer 2

使用宏get_user不正确。

它的第一个参数应该是变量名，而不是它的地址。

它的第二个参数应该是指向用户空间数据的类型的指针。该指针的确切类型用于确定要读取的数据的大小。

正确：

    long userOperand;
    ...
    get_user(userOperand, (const long __user*)buffer);

    printk(KERN_NOTICE "Value written: %ld\n", userOperand);

注意第二个参数的情况: read long而不是char需要它(因为buffer参数是指向char的指针)。

注意，上面的代码没有使用您的userInput变量，所以您不需要定义它，也不需要分配内存。

注意，可以用任何.write参数调用count方法，该参数表示从用户传递的的字节数。由于get_user总是尝试读取一个预定义的字节数(在您的例子中，这个数字等于long的大小)，所以对于check来说，count是否等于该数字(或者至少不小于给定的数字)是对用户友好的：

if (count != sizeof(long)) {
  return -EINVAL;
}