tech-net: Re: new mbuf API

Subject: Re: new mbuf API
To: Pavel Cahyna <pavel@NetBSD.org>
From: Greg Troxel <gdt@ir.bbn.com>
List: tech-net
Date: 04/20/2007 13:40:16

 What I've missed there was a description of "guaranteed contiguous
 data". The problem is that one function can make part of the mbuf chanin
 contiguous (like m_pulldown or one of the new functions), but a
 subsequent call can fragment the chain again. To prevent this, I have
 introduced the notion of "guaranteed contiguous data". If a function
 makes a range of a mbuf chain contiguous, it also marks it as a
 guaranteed contiguous region and subsequent calls to mbuf rearranging
 functions must keep it contiguous.
If it's not safe for a caller to assume it's still true, then the word
guaranteed shouldn't be used. What you're describing is more like an
efficiency hint. This also seems complicated, and if a caller can't
safely omit checks, I'm not sure how much is gained.