Aspects pratiques : Pilotes orientés caractère

Exemple: open et release

static int skeleton_open(struct inode* i, struct file* f)
{
    pr_info("skeleton : open operation... major:%d, minor:%d\n",
            imajor(i),
            iminor(i));
    if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) != 0) {
        pr_info("skeleton : opened for reading & writing...\n");
    } else if ((f->f_mode & FMODE_READ) != 0) {
        pr_info("skeleton : opened for reading...\n");
    } else if ((f->f_mode & FMODE_WRITE) != 0) {
        pr_info("skeleton : opened for writing...\n");
    }
    return 0;
}

static int skeleton_release(struct inode* i, struct file* f)
{
    pr_info("skeleton: release operation...\n");
    return 0;
}

Exemple: read

#define BUFFER_SZ 10000
static char s_buffer[BUFFER_SZ];
static ssize_t skeleton_read(struct file* f,
                             char __user* buf,
                             size_t count,
                             loff_t* off)
{
    // compute remaining bytes to copy, update count and pointers
    ssize_t remaining = BUFFER_SZ - (ssize_t)(*off);
    char* ptr         = s_buffer + *off;
    if (count > remaining) count = remaining;
    *off += count;
    // copy required number of bytes
    if (copy_to_user(buf, ptr, count) != 0) count = -EFAULT;
    pr_info("skeleton: read operation... read=%ld\n", count);
    return count;
}

Exemple: write

static ssize_t skeleton_write(struct file* f,
                              const char __user* buf,
                              size_t count,
                              loff_t* off)
{
    // compute remaining space in buffer and update pointers
    ssize_t remaining = BUFFER_SZ - (ssize_t)(*off);
    // check if still remaining space to store additional bytes
    if (count >= remaining) count = -EIO;
    // store additional bytes into internal buffer
    if (count > 0) {
        char* ptr = s_buffer + *off;
        *off += count;
        ptr[count] = 0;  // make sure string is null terminated
        if (copy_from_user(ptr, buf, count)) count = -EFAULT;
    }
    pr_info("skeleton: write operation... written=%ld\n", count);
    return count;
}

Exemple: enregistrement et libération

static dev_t skeleton_dev;
static struct cdev skeleton_cdev;
static int __init skeleton_init(void)
{
    int status = alloc_chrdev_region(&skeleton_dev, 0, 1, "mymodule");
    if (status == 0) {
        cdev_init(&skeleton_cdev, &skeleton_fops);
        skeleton_cdev.owner = THIS_MODULE;
        status              = cdev_add(&skeleton_cdev, skeleton_dev, 1);
    }
    pr_info("Linux module skeleton loaded\n");
    return 0;
}

static void __exit skeleton_exit(void)
{
    cdev_del(&skeleton_cdev);
    unregister_chrdev_region(skeleton_dev, 1);
    pr_info("Linux module skeleton unloaded\n");
}