---
title: ctl_register
framework: Kernel
role: symbol
role_heading: Function
platforms: [macOS 10.13+]
path: kernel/1809176-ctl_register
---

# ctl_register

## Declaration

```occ
errno_t ctl_register(struct kern_ctl_reg *userkctl, kern_ctl_ref *kctlref);
```

## Parameters

- `userkctl`: A structure defining the kernel control to be attached. The ctl_connect callback must be specified, the other callbacks are optional. If ctl_connect is set to zero, ctl_register fails with the error code EINVAL.
- `kctlref`: Upon successful return, the kctlref will contain a reference to the attached kernel control. This reference is used to unregister the kernel control. This reference will also be passed in to the callbacks each time they are called.

## Return Value

Return Value 0 - Kernel control was registered. EINVAL - The registration structure was not valid. ENOMEM - There was insufficient memory. EEXIST - A controller with that id/unit is already registered.

## Discussion

Discussion Register a kernel control. This will enable clients to connect to the kernel control using a PF_SYSTEM socket.

## See Also

### control

- [ctl_deregister](kernel/1809161-ctl_deregister.md)
- [ctl_enqueuedata](kernel/1809168-ctl_enqueuedata.md)
- [ctl_enqueuembuf](kernel/1809171-ctl_enqueuembuf.md)
- [ctl_getenqueuereadable](kernel/2919907-ctl_getenqueuereadable.md)
- [ctl_getenqueuespace](kernel/1809173-ctl_getenqueuespace.md)