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From: gwyn@brl-smoke.ARPA (Doug Gwyn )
Newsgroups: comp.lang.c
Subject: Re: System V manuals (was Re: What real non-UNIX 'C' compilers...)
Message-ID: <6517@brl-smoke.ARPA>
Date: Sun, 4-Oct-87 01:21:28 EDT
Article-I.D.: brl-smok.6517
Posted: Sun Oct  4 01:21:28 1987
Date-Received: Wed, 7-Oct-87 04:16:51 EDT
References: <855@sugar.UUCP>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 51

In article <855@sugar.UUCP> peter@sugar.UUCP (Peter da Silva) writes:
>The UNIX System User's Manual.
>ISBN 0-13-938242-9 025

I use that for convenience (1 volume instead of 3), but it's horribly
organized compared with the real UNIX System V manuals.  Prentice-Hall
is also publishing what amounts to the generically useful part of the
SVR3.0 documentation set in softcover, but there have been reports of
typesetting botches that weren't in the SVR3.0 manuals.  Since they
seem to have the same contents, I wonder how that happened.

>I don't believe you could implement "read" as a library routine and retain the
>attribute of leaving the file descriptor at the point last read, unless you
>were to "implement" it by making a direct call to the existing read routine.
>Certainly buffering would be out.

Well, of COURSE buffering is out, because that's not what read() a la
POSIX/SVID is supposed to do!  Here's mine:

/*
	read -- system call emulation for 4.2BSD

	last edit:	16-Jun-1983	D A Gwyn

	The only reason for this layer is to support O_NDELAY mode.
*/

#include	<errno.h>

extern int	errno;
extern int	_read();		/* actual system call */

int
read( fildes, buf, nbyte )
	int	fildes;
	char	*buf;
	int	nbyte;
	{
	register int	serrno = errno; /* save errno */
	register int	nread;

	if ( (nread = _read( fildes, buf, nbyte )) >= 0
	  || errno != EWOULDBLOCK
	   )
		return nread;

	/* O_NDELAY set and read would block: */

	errno = serrno; 		/* restore errno */
	return 0;
	}