内核态读写串口

在Linux内核中，可以使用 `tty` 子系统提供的接口进行串口读写。以下是一个简单的内核态串口读写程序的示例：

#include <linux/module.h>
#include <linux/init.h>
#include <linux/serial.h>
#include <linux/tty.h>
#include <linux/tty_driver.h>

#define SERIAL_PORT "/dev/ttyS0"

static struct tty_driver *serial_driver;
static struct tty_port serial_port;

static int serial_open(struct tty_struct *tty, struct file *file) {
    return tty_port_open(&serial_port, tty, file);
}

static void serial_close(struct tty_struct *tty, struct file *file) {
    tty_port_close(&serial_port, tty, file);
}

static int serial_write(struct tty_struct *tty, const unsigned char *buf, int count) {
    return tty_write(tty, buf, count);
}

static int serial_write_room(struct tty_struct *tty) {
    return tty_write_room(tty);
}

static int serial_chars_in_buffer(struct tty_struct *tty) {
    return tty->port->tty->count;
}

static const struct tty_operations serial_ops = {
    .open = serial_open,
    .close = serial_close,
    .write = serial_write,
    .write_room = serial_write_room,
    .chars_in_buffer = serial_chars_in_buffer,
};

static int __init serial_init(void) {
    int ret;

    // 初始化串口端口
    ret = tty_port_init(&serial_port);
    if (ret) {
        printk(KERN_ERR "Failed to initialize tty port\n");
        return ret;
    }

    // 注册串口驱动
    serial_driver = alloc_tty_driver(1);
    if (!serial_driver) {
        printk(KERN_ERR "Failed to allocate tty driver\n");
        tty_port_destroy(&serial_port);
        return -ENOMEM;
    }

    serial_driver->owner = THIS_MODULE;
    serial_driver->driver_name = "serial";
    serial_driver->name = "ttyS0";
    serial_driver->major = 0;
    serial_driver->minor_start = 0;
    serial_driver->type = TTY_DRIVER_TYPE_SERIAL;
    serial_driver->subtype = SERIAL_TYPE_NORMAL;
    serial_driver->flags = TTY_DRIVER_REAL_RAW;
    serial_driver->init_termios = tty_std_termios;
    tty_set_operations(serial_driver, &serial_ops);

    ret = tty_register_driver(serial_driver);
    if (ret) {
        printk(KERN_ERR "Failed to register tty driver\n");
        put_tty_driver(serial_driver);
        tty_port_destroy(&serial_port);
        return ret;
    }

    tty_port_link_device(&serial_port, serial_driver, 0);

    printk(KERN_INFO "Serial driver initialized\n");

    return 0;
}

static void __exit serial_exit(void) {
    tty_unregister_driver(serial_driver);
    put_tty_driver(serial_driver);
    tty_port_destroy(&serial_port);
    printk(KERN_INFO "Serial driver unloaded\n");
}

module_init(serial_init);
module_exit(serial_exit);
MODULE_LICENSE("GPL");

该程序首先初始化了 `tty` 端口，并注册了一个名为 "serial" 的 `tty` 驱动。接着，程序将 "ttyS0" 设备与该驱动连接起来，并定义了对应的 `tty_operations` 结构体，实现了串口的打开、关闭、写入等功能。最后，程序在 `init` 函数中注册了该驱动，在 `exit` 函数中注销该驱动。注意，在编写内核态程序时，需要使用内核提供的 API，而不是标准 C 库中的函数。