From mboxrd@z Thu Jan  1 00:00:00 1970
From: presotto@closedmind.org
To: 9fans@cse.psu.edu
Subject: Re: [9fans] isatty
MIME-Version: 1.0
Content-Type: multipart/mixed;
	boundary="upas-qmqgwwpuzbbtrpfponmkrxflxc"
Message-Id: <20020123131345.E12DA199BF@mail.cse.psu.edu>
Date: Wed, 23 Jan 2002 08:13:44 -0500
Topicbox-Message-UUID: 41f38fae-eaca-11e9-9e20-41e7f4b1d025

This is a multi-part message in MIME format.
--upas-qmqgwwpuzbbtrpfponmkrxflxc
Content-Disposition: inline
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit

The version comparison is an overkill and potentially wrong since
whatever is implementing /dev/cons may decide to update the
version each write, as is our practice in other places.

That should work in general as long as the namespace hasn't
been changed twixt the opening of the fd and the dirstat.
Otherwise /dev/cons may be under a different mount point
number and hence a different c.dev.

The question isatty is usually trying to answer is
"does the fd has an interacting user behind it?".  A
hard question to answer in a world where the geography
can shift so easily.

--upas-qmqgwwpuzbbtrpfponmkrxflxc
Content-Type: message/rfc822
Content-Disposition: inline

Received: from plan9.cs.bell-labs.com ([135.104.9.2]) by plan9; Wed Jan 23 06:57:37 EST 2002
Received: from mail.cse.psu.edu ([130.203.4.6]) by plan9; Wed Jan 23 06:57:36 EST 2002
Received: from psuvax1.cse.psu.edu (psuvax1.cse.psu.edu [130.203.20.6])
	by mail.cse.psu.edu (CSE Mail Server) with ESMTP
	id DB00019A02; Wed, 23 Jan 2002 06:57:06 -0500 (EST)
Delivered-To: 9fans@cse.psu.edu
Received: from theraft.strakt.com (theraft.strakt.com [62.13.29.34])
	by mail.cse.psu.edu (CSE Mail Server) with ESMTP id C5749199F2
	for <9fans@cse.psu.edu>; Wed, 23 Jan 2002 06:56:46 -0500 (EST)
Received: from strakt.com (zode.strakt.com [62.13.29.39])
	by theraft.strakt.com (8.12.1/8.12.1/Debian -5) with ESMTP id g0NBui7U014950
	for <9fans@cse.psu.edu>; Wed, 23 Jan 2002 12:56:44 +0100
Message-ID: <3C4EA4FC.A777CA4D@strakt.com>
From: Boyd Roberts <boyd@strakt.com>
Organization: AB Strakt
X-Mailer: Mozilla 4.77 [en] (X11; U; Linux 2.4.17 i686)
X-Accept-Language: en
MIME-Version: 1.0
To: "9fans@cse.psu.edu" <9fans@cse.psu.edu>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Subject: [9fans] isatty
Sender: 9fans-admin@cse.psu.edu
Errors-To: 9fans-admin@cse.psu.edu
X-BeenThere: 9fans@cse.psu.edu
X-Mailman-Version: 2.0.8
Precedence: bulk
Reply-To: 9fans@cse.psu.edu
List-Help: <mailto:9fans-request@cse.psu.edu?subject=help>
List-Id: Fans of the OS Plan 9 from Bell Labs <9fans.cse.psu.edu>
List-Archive: <https://lists.cse.psu.edu/archives/9fans/>
Date: Wed, 23 Jan 2002 12:56:44 +0100

Given I had to implement this 'thing' on Plan 9 I decided on:

#include <u.h>
#include <libc.h>

static char *cons = "/dev/cons";

/*
 * Compare fd to cons should get it right.
 */
int
isatty(int fd)
{
	Dir c;
	Dir f;

	if (dirstat(cons, &c) != 0)
		return 0;

	if (dirfstat(fd, &f) != 0)
		return 0;

	return f.type == c.type &&
		f.dev == c.dev &&
		f.qid.path == c.qid.path &&
		f.qid.vers == c.qid.vers;
}

Seemed obvious to me, but is this a good plan?

The overkill on the multiple dirstat's on /dev/cons and
qid comparison I thought would ensure that I wouldn't
get fooled [again].
--upas-qmqgwwpuzbbtrpfponmkrxflxc--