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From: guy%gorodish@Sun.COM (Guy Harris)
Newsgroups: comp.unix.wizards
Subject: Re: Determining the max number of open files on System V
Message-ID: <20117@sun.uucp>
Date: Mon, 1-Jun-87 15:39:24 EDT
Article-I.D.: sun.20117
Posted: Mon Jun  1 15:39:24 1987
Date-Received: Wed, 3-Jun-87 01:39:26 EDT
References: <3635@spool.WISC.EDU>
Sender: news@sun.uucp
Lines: 37
Keywords: NOFILES, S5R3
Summary: UNIX documentation is a contradiction in terms

> I'm trying to port a program from BSD to Sys V Rel. 3.  Along the way,
> it tries to close all of its file descriptors.  On BSD you just call
> getdtablesize() to find how many to close, but I can't seem to find
> the equivalent on S5R3.
> 
> So, where do I get the real value?  What is "v.v_nofiles" and how do
> I get at it's value?

You do

	ulimit(4, 0L);

and the returned value is the maximum number of file descriptors.  Or,
preferably, you do

	int
	getdtablesize()
	{
		extern long ulimit();

		return (ulimit(4, 0L));
	}

and obviate the need to fix all occurrences of "getdtablesize".

No, this isn't documented.  It seems AT&T is maintaining the proud
"use the Force, read the Source" tradition of earlier UNIX
releases....  (They also seem to be maintaining the equally proud
"different for its own sake" or "Not Invented Here" tradition; why
the hell couldn't they have added a "getdtablesize" system call, or
even just supplied a wrapper around "ulimit"?  Whether they like it
or not, "getdtablesize" is as close as you can get to a *de facto*
standard name for the routine that returns the size of the
per-process file table.)
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com