---
title: mbuf_tag_id_find
framework: Kernel
role: symbol
role_heading: Function
platforms: [macOS 10.4+]
path: kernel/1535795-mbuf_tag_id_find
---

# mbuf_tag_id_find

## Declaration

```occ
errno_t mbuf_tag_id_find(const char *module_string, mbuf_tag_id_t *module_id);
```

## Parameters

- `module_string`: A unique string identifying your module. Example: com.apple.nke.SharedIP.
- `module_id`: Upon return, a unique identifier for use with mbuf_tag_* functions. This identifier is valid until the machine is rebooted.

## Return Value

Return Value 0 upon success otherwise the errno error.

## Discussion

Discussion Lookup the module id for a string. If there is no module id assigned to this string, a new module id will be assigned. The string should be the bundle id of the kext. In the case of a tag that will be shared across multiple kexts, a common bundle id style string should be used. The lookup operation is not optimized. A module should call this function once during startup and chache the module id. The module id will not be resassigned until the machine reboots.