---
title: ctl_getopt_func
framework: Kernel
role: symbol
role_heading: Type Alias
platforms: [macOS 10.13+]
path: kernel/ctl_getopt_func
---

# ctl_getopt_func

## Declaration

```occ
typedef errno_t (*ctl_getopt_func)(kern_ctl_ref kctlref, u_int32_t unit, void *unitinfo, int opt, void *data, size_t *len);
```

## Parameters

- `kctlref`: The control ref of the kernel control.
- `unit`: The unit number of the kernel control instance.
- `unitinfo`: The user-defined private data initialized by the ctl_connect_func callback.
- `opt`: The socket option.
- `data`: A buffer to copy the results in to. May be NULL, see discussion.
- `len`: A pointer to the length of the buffer. This should be set to the length of the buffer used before returning.

## Discussion

Discussion The ctl_getopt_func is used to handle client get socket option requests for the SYSPROTO_CONTROL option level. A buffer is allocated for storage and passed to your function. The length of that buffer is also passed. Upon return, you should set *len to length of the buffer used. In some cases, data may be NULL. When this happens, *len should be set to the length you would have returned had data not been NULL. If the buffer is too small, return an error.