sed2 driver – code implementation

In terms of code, the ioctl() method's code within the sed2 driver for the encrypt operation is as follows (for clarity, we won't show all the error checking code here; we will show only the most relevant parts). You can find the full code at ch5/sed2/:

// ch5/sed2/sed2_driver/sed2_drv.c
[ ... ]
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 36)
static long ioctl_miscdrv(struct file *filp, unsigned int cmd, unsigned long arg)
#else
static int ioctl_miscdrv(struct inode *ino, struct file *filp, unsigned int cmd, unsigned long arg)
#endif
{
    struct stMyCtx *priv = gpriv;

[ ... ]
switch (cmd) {
    case IOCTL_LLKD_SED_IOC_ENCRYPT_MSG: /* kthread: encrypts the msg passed in */
        [ ... ]
        if (atomic_read(&priv->msg_state) == XF_ENCRYPT) { // already encrypted?
            pr_notice("encrypt op: message is currently encrypted; aborting op...\n");
            return -EBADRQC; /* 'Invalid request code...