From owner-freebsd-hackers  Tue Apr 22 12:51:14 1997
Return-Path: <owner-hackers>
Received: (from root@localhost)
          by hub.freebsd.org (8.8.5/8.8.5) id MAA17696
          for hackers-outgoing; Tue, 22 Apr 1997 12:51:14 -0700 (PDT)
Received: from sax.sax.de (sax.sax.de [193.175.26.33])
          by hub.freebsd.org (8.8.5/8.8.5) with SMTP id MAA17647
          for <hackers@freebsd.org>; Tue, 22 Apr 1997 12:51:08 -0700 (PDT)
Received: (from uucp@localhost) by sax.sax.de (8.6.12/8.6.12-s1) with UUCP id VAA16798 for hackers@freebsd.org; Tue, 22 Apr 1997 21:51:06 +0200
Received: (from j@localhost)
	by uriah.heep.sax.de (8.8.5/8.8.5) id VAA28956;
	Tue, 22 Apr 1997 21:45:31 +0200 (MET DST)
Message-ID: <19970422214531.BX39690@uriah.heep.sax.de>
Date: Tue, 22 Apr 1997 21:45:31 +0200
From: j@uriah.heep.sax.de (J Wunsch)
To: hackers@freebsd.org
Subject: Re: concurrent calls to device drivers
References: <199704210727.JAA15119@labinfo.iet.unipi.it> <199704220425.NAA12940@genesis.atrad.adelaide.edu.au>
X-Mailer: Mutt 0.60_p2-3,5,8-9
Mime-Version: 1.0
X-Phone: +49-351-2012 669
X-PGP-Fingerprint: DC 47 E6 E4 FF A6 E9 8F  93 21 E0 7D F9 12 D6 4E
Reply-To: joerg_wunsch@uriah.heep.sax.de (Joerg Wunsch)
In-Reply-To: <199704220425.NAA12940@genesis.atrad.adelaide.edu.au>; from Michael Smith on Apr 22, 1997 13:55:07 +0930
Sender: owner-hackers@freebsd.org
X-Loop: FreeBSD.org
Precedence: bulk

As Michael Smith wrote:

> That's ususally the best way to go; something like :
> 
> 
> 	sc_busy;
> 
> ...
> 
> fooread(...)
> {
> ...
> 
> 	s = splfoo();
> 	while(sc->sc_busy) {

What's the splfoo() for?

Unless the interrupt service can modify sc_busy, you don't need to
protect it.

You gotta do a

	obtain_mp_lock();
	while(sc->sc_busy) {
		...
	}
	release_mp_lock();

however. :-)  On a uniprocessor however, only one process can be in
the kernel at a time.

-- 
cheers, J"org

joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ -- NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)