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Newsgroups: comp.unix.bsd Path: sserve!newshost.anu.edu.au!munnari.oz.au!news.Hawaii.Edu!ames!elroy.jpl.nasa.gov!ncar!destroyer!cs.ubc.ca!van-bc!inde!newshost!gday From: gday@ignatz.inde.bc.ca (Gordon Day) Subject: Re: mbuf documentation ? In-Reply-To: medira@cs.tu-berlin.de's message of 27 Apr 1993 18:32:31 GMT Message-ID: <GDAY.93Apr28110418@ignatz.inde.bc.ca> Sender: news@inde.bc.ca Organization: INDE Electronics, Inc. References: <1rju7v$jvg@news.cs.tu-berlin.de> Date: Wed, 28 Apr 1993 19:04:18 GMT Lines: 25 >>>"cornelia" == Cornelia Langenkamp <medira@cs.tu-berlin.de> writes: cornelia> Does anybody know why the mbuf-structure has the specified cornelia> length of 128 Byte ? Is there any historical reason for cornelia> that ? I'd be glad to get some advice for any documentation cornelia> about mbufs at all. My guess is that the 128 byte length is the only power of two that wasn't too big/small for what the mbufs intended purpose was: packet handling. The power of two is nice for things like: /* address in mbuf to mbuf head */ #define dtom(x) ((struct mbuf *)((int)x & ~(MSIZE-1))) Check out "The Design and Implementation of the 4.3BSD Operating System" by Leffler, McKusick, Karels, and Quarterman (ISBN 0-201-06196-1) This gives an overview of the mbuf structure. Ta, Gordon. _______________________________________________________________________________ gordon day, inde electronics, +1-604-430-1446.