c
struct pci_dn *PCI_DN(dn){
    if (!dn || !dn->data) {
        // Input validation failed
        return NULL; // or handle error
    }
    // Perform additional validation if necessary
    // For example, check the structure of dn->data to ensure it matches struct pci_dn
    struct pci_dn *pci_dn = (struct pci_dn *)dn->data;
    if (pci_dn->magic != PCI_DN_MAGIC || // Example validation
        pci_dn->size != sizeof(struct pci_dn)) {
        // Validation failed
        return NULL; // or handle error
    }
    return pci_dn;
}
