Inside Macintosh: Networking With Open Transport / Part 2 - Open Transport Reference

Chapter 28 - Advanced Topics Reference / Constants and Data Types

OTBuffer Constant

When receiving data without making a copy, you need to pass an OTBuffer pointer as your data buffer pointer. Open Transport provides a constant that you can use instead of the nbytes parameter of the OTRcv function or the udata.maxlen field used with other receive functions to indicate that you are doing this.

enum {
   kNetbufDataIsOTBufferStar= 0xfffffffd
};