3.用户程序与驱动交互

驱动程序请使用第二章https://blog.csdn.net/chenhequanlalala/article/details/140034424

用户app与驱动交互最常见的做法是insmod驱动后，生成一个设备节点，app通过open，read等系统调用去操作这个设备节点，这里先用mknode命令调试。

mknod 设备名设备类型(b块设备/c字符设备/p管道) 主设备号次设备号

mknod /dev/hello c 240 0

使用mknode后生成了/dev/hello节点，写入数据到hello节点中，查看dmesg的输出发现调用了驱动的open write release

echo 1 > /dev/hello
[ 802.771723] /home/book/nfs_rootfs/drivers_projects/01_hello_drv/hello_drv.c hello_open 48

[ 802.773196] /home/book/nfs_rootfs/drivers_projects/01_hello_drv/hello_drv.c hello_write 40

[ 802.773285] /home/book/nfs_rootfs/drivers_projects/01_hello_drv/hello_drv.c hello_release 56

这里写一个C程序来读写这个设备节点

#include "linux/string.h"
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>

/*
读数据 ./hello_test xxx(设备节点名字)
写数据 ./hello_test xxx(设备节点名字) string
*/

int main(int argc, char **argv)
{
    int fd;
    int len;
    char buf[1024];

    if(argc < 2)
    {
        printf("Usage :\n");
        printf("%s <dev> [str]\n", argv[0]);
        return -1;
    }

    //open
    fd = open(argv[1], O_RDWR);
    if(fd < 0)
    {
        printf("open %s failed\n", argv[1]);
        return -1;
    }

    //read
    if(argc == 2)
    {
        len = read(fd, buf, sizeof(buf));
        printf("%s\n", buf);
    }
    //write
    else if(argc == 3)
    {
        len = write(fd, argv[2], strlen(argv[2]));
    }
    else
    {
        printf("Too many parameters\n");
    }

    close(fd);
}

分别调用 ./hello_test /dev/hello 123 和 ./hello_test /dev/hello 后，查看dmesg输出显示

[ 2770.434595] /home/book/nfs_rootfs/drivers_projects/01_hello_drv/hello_drv.c hello_open 48

[ 2770.434664] /home/book/nfs_rootfs/drivers_projects/01_hello_drv/hello_drv.c hello_write 40

[ 2770.434705] /home/book/nfs_rootfs/drivers_projects/01_hello_drv/hello_drv.c hello_release 56

[ 2772.388372] /home/book/nfs_rootfs/drivers_projects/01_hello_drv/hello_drv.c hello_open 48

[ 2772.388439] /home/book/nfs_rootfs/drivers_projects/01_hello_drv/hello_drv.c hello_read 32

[ 2772.389257] /home/book/nfs_rootfs/drivers_projects/01_hello_drv/hello_drv.c hello_release 56

app的open write read release都一一对应上了。

这里的./hello_test /dev/hello其实没有读到数据，打印如下，原因下一章再说。

[root@100ask:/mnt/drivers_projects/01_hello_drv]# ./hello_test /dev/hello

read size = 1024 data =