6

所以我正在通过内核驱动程序编程工作，目前我正在尝试在应用程序和内核驱动程序之间构建一个简单的数据传输。

我正在使用简单的字符设备作为这两者之间的链接，并且我已经成功地将数据传输到驱动程序，但是我无法将有意义的数据返回到用户空间。

内核驱动程序如下所示：

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h> /* printk() */
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <linux/proc_fs.h>
#include <asm/uaccess.h> /* copy_from/to_user */

MODULE_LICENSE("GPL");

//Declarations
int memory_open(struct inode *inode, struct file *filp);
int memory_release(struct inode *inode, struct file *filp);
ssize_t memory_read(struct file *filp, char *buf, size_t count, loff_t *f_pos);
ssize_t memory_write(struct file *filp, char *buf, size_t count, loff_t *f_pos);
void memory_exit(void);
int memory_init(void);

/* Structure that declares the usual file access functions */
struct file_operations memory_fops = {
    read: memory_read,
    write: memory_write,
    open: memory_open,
    release: memory_release
};

//Default functions
module_init(memory_init);
module_exit(memory_exit);

/* Global variables of the driver */
/* Major number */
int memory_major = 60;
/* Buffer to store data */
char* tx_buffer;
char* rx_buffer;

int BUFFER_SIZE=64;
int actual_rx_size=0;

int memory_init(void) {
    int result;

    /* Registering device */
    result = register_chrdev(memory_major, "move_data", &memory_fops);
    if (result < 0) {
        printk(
        "<1>move_data: cannot obtain major number %d\n", memory_major);
        return result;
    }

    /* Allocating memory for the buffers */
    //Allocate buffers
    tx_buffer = kmalloc(BUFFER_SIZE,  GFP_KERNEL);
    rx_buffer = kmalloc(BUFFER_SIZE,  GFP_KERNEL);

    //Check allocation was ok
    if (!tx_buffer || !rx_buffer) {
        result = -ENOMEM;
        goto fail;
    }

    //Reset the buffers
    memset(tx_buffer,0, BUFFER_SIZE);
    memset(rx_buffer,0, BUFFER_SIZE);

    printk("<1>Inserting memory module\n"); 
    return 0;

    fail:
        memory_exit(); 
        return result;
}

void memory_exit(void) {
    /* Freeing the major number */
    unregister_chrdev(memory_major, "memory");

    /* Freeing buffers */
    if (tx_buffer) {
        kfree(tx_buffer); //Note kfree
    }

    if (rx_buffer) {
        kfree(rx_buffer); //Note kfree
    }
    printk("<1>Removing memory module\n");
}


//Read function
ssize_t memory_read(struct file *filp, char *buf, size_t count, loff_t *f_pos) { 

    printk("user requesting data, our buffer has (%d) \n", actual_rx_size);

    /* Transfering data to user space */ 
    int retval = copy_to_user(buf,rx_buffer,actual_rx_size);

    printk("copy_to_user returned (%d)", retval);

    return retval;
}

ssize_t memory_write( struct file *filp, char *buf,
                  size_t count, loff_t *f_pos) {

    //zero the input buffer
    memset(tx_buffer,0,BUFFER_SIZE);
    memset(rx_buffer,0,BUFFER_SIZE);

    printk("New message from userspace - count:%d\n",count);

    int retval = copy_from_user(tx_buffer,buf,count);

    printk("copy_from_user returned (%d) we read [%s]\n",retval , tx_buffer);
    printk("initialize rx buffer..\n");

    memcpy(rx_buffer,tx_buffer, count);
    printk("content of rx buffer [%s]\n", rx_buffer);

    actual_rx_size = count;

    return count; //inform that we read all (fixme?)
}

//Always successfull
int memory_open(struct inode *inode, struct file *filp) { return 0; }
int memory_release(struct inode *inode, struct file *filp) { return 0; }

用户空间应用程序也很简单：

#include <unistd.h>     //open, close | always first, defines compliance
#include <fcntl.h>      //O_RDONLY
#include <stdio.h>
#include <stdlib.h>     //printf
#include <string.h>

int main(int args, char *argv[])
{
int BUFFER_SIZE = 20;

char internal_buf[BUFFER_SIZE];
int to_read = 0;

memset(internal_buf,0,BUFFER_SIZE);

if (args < 3) {
    printf("2 Input arguments needed\nTo read 10 bytes: \"%s read 10\" \
    \nTo write string \"hello\": \"%s write hello\"\nExiting..\n", argv[0], argv[0]);
    return 1;
}


//Check the operation
if (strcmp(argv[1],"write") == 0) {

    printf("input lenght:%d", strlen(argv[2]));
    //Make sure our write fits to the internal buffer
    if(strlen(argv[2]) >= BUFFER_SIZE) {
        printf("too long input string, max buffer[%d]\nExiting..", BUFFER_SIZE);
        return 2;
    }

    printf("write op\n");
    memcpy(internal_buf,argv[2], strlen(argv[2]));

    printf("Writing [%s]\n", internal_buf);

    FILE * filepointer;
    filepointer = fopen("/dev/move_data", "w");
    fwrite(internal_buf, sizeof(char) , strlen(argv[2]), filepointer);
    fclose(filepointer);

} else if (strcmp(argv[1],"read") == 0) {
    printf("read op\n");

    to_read = atoi(argv[2]);

    FILE * filepointer;
    filepointer = fopen("/dev/move_data", "r");
    int retval = fread(internal_buf, sizeof(char) , to_read, filepointer);
    fclose(filepointer);

    printf("Read %d bytes from driver string[%s]\n", retval, internal_buf);
} else {
    printf("first argument has to be 'read' or 'write'\nExiting..\n");
    return 1;
}


return 0;
}

当我执行我的应用程序时，会发生以下情况：

./rw write "testing testing"

kernel side:
[ 2696.607586] New message from userspace - count:15
[ 2696.607591] copy_from_user returned (0) we read [testing testing]
[ 2696.607593] initialize rx buffer..
[ 2696.607594] content of rx buffer [testing testing]

所以一切看起来都是正确的。但是当我尝试阅读时：

./rw read 15
read op
Read 0 bytes from driver string[]

Kernel 
[  617.096521] user requesting data, our buffer has (15) 
[  575.797668] copy_to_user returned (0)
[  617.096528] copy_to_user returned (0)

我想我做错了什么很简单，因为如果我不返回 0，我可以取回一些数据，但是例如如果我用 cat 阅读，它将继续无休止地循环。

我想了解我在思考中犯了哪些错误。有没有办法让内核驱动程序只吐出它的缓冲区，然后返回 0，这样我就不必在两者之间建立一些协议来处理读取了多少数据等。

感谢您的建议！

编辑：更正了 memory_write 函数中的 printk 语句，并添加了 memory_read 函数跟踪

4

1 回答 1

6

您的 read 函数始终返回 0 因为您正在返回retval，而不是读取的字节数。只要copy_to_user()调用始终成功，retval就永远为0。相反，只要copy_to_user()成功，就应该返回实际写入用户空间的字节数。该文档声明copy_to_user()返回无法复制的字节总数。

顺便说一句，您忽略了计数的值。用户请求的数据很可能比缓冲区中可用的数据少。你永远不应该忽略计数。

现在您遇到了函数从不返回 0 的问题。返回 0 很重要，因为它告诉用户应用程序没有更多数据可供读取，并且用户应用程序应该关闭设备文件。

您需要在驱动程序中跟踪已读取的字节数与已写入的字节数。这可以使用您的actual_rx_size.

尝试这个：

//Read function
ssize_t memory_read(struct file *filp, char *buf, size_t count, loff_t *f_pos) { 

    ssize_t bytes;

    if (actual_rx_size < count)
        bytes = actual_rx_size;
    else
        bytes = count;

    printk("user requesting data, our buffer has (%d) \n", actual_rx_size);

    /* Check to see if there is data to transfer */
    if (bytes == 0)
        return 0;

    /* Transfering data to user space */ 
    int retval = copy_to_user(buf,rx_buffer,bytes);

    if (retval) {
        printk("copy_to_user() could not copy %d bytes.\n", retval);
        return -EFAULT;
    } else {
        printk("copy_to_user() succeeded!\n");
        actual_rx_size -= bytes;
        return bytes;
    }
}
于 2013-06-08T14:56:17.427 回答