Read and write to Arduino serial using a kernel module

I am writing a network driver that should send packets to an Arduino using Serial communication. This is a homework assignment and this is only for educational purposes. Please, take that into account before suggesting that everything could be accomplished in user space.

This answer stated about filp_open and filp_close, and I thought that I could use them to open /dev/ttyACMx or /dev/ttyUSBx, but I read somewhere else that it is not a good idea to use I/O file operations inside the kernel, so I am looking for a better approach.

I have also read about outb and inb, but I have not found any way to get the port number argument required for both functions. I have tried using lsusb and writing to some of those 0xXX endpoint addresses but it did not work.

This is my transmit function, where I want to, instead of printing, writing to a serial port. My aux variable is just a union that contains two members: struct sk_buff skb and unsigned char bytes[sizeof(struct sk_buff)]. But at this point in the assignment, I just want to send the contents of skb.data to my Arduino serial.

aux = skb;
while(aux != NULL) {
    p.skb = *aux;
    for(i = 0; i < p.skb.len; i++) {
        if(i == 0) {
            printk(KERN_INFO "\\%02x", p.skb.data[i]);
        }
        else {
            printk(KERN_CONT "\\%02x", p.skb.data[i]);
        }

    }
    aux = aux->next;
}

And this is Arduino code is the following:

void setup() {
    Serial.begin(9600);
    Serial.println("Start");
}
void loop() {
    while(Serial.available() > 0)
        Serial.print(Serial.read());

    Serial.println();
}

It is simple as that. I want to read the content of a packet inside my Arduino. How can I write in a /dev/ttyACMx or /dev/ttyUSBx port inside my network driver?