Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!rutgers!att!cbnewsl!sar0
From: sar0@cbnewsl.att.com (stephen.a.rago)
Newsgroups: comp.unix.questions
Subject: Re: reliable reads from pipes
Message-ID: <1990Aug13.171223.7653@cbnewsl.att.com>
Date: 13 Aug 90 17:12:23 GMT
References: <1990Aug3.233256.29659@NCoast.ORG> <712@tetrauk.UUCP> <1827@necisa.ho.necisa.oz>
Organization: AT&T Bell Laboratories
Lines: 25

In article <1827@necisa.ho.necisa.oz>, boyd@necisa.ho.necisa.oz (Boyd Roberts) writes:
> In article <11155@alice.UUCP> andrew@alice.UUCP (Andrew Hume) writes:
> >
> >	lest anyone start relying on reads returning whatever is in the pipe,
> >9th edition and later unices preserved the size of the writes which can
> >now also exceed the size of the pipe buffer (i think).
> 
> Not to mention the 1 byte write nasty that will take out all your
> stream message buffers.  The stream pipe fills when the write
> side high water mark is hit; which is tunable.

SVR4 won't let someone "take all the stream message buffers" unless
they are running as root.  And it's not message buffers, its general
memory out of the kernel memory pool.

> 
> Those M_DELIM's are neat...
> 

M_DELIM's are old.  In V10 it's a flag in the message header (except for
the message line discipline).  SVR4 also has delimiters, if you want to
use them.

Steve Rago
sar@attunix.att.com