From owner-freebsd-current@FreeBSD.ORG Tue Feb 17 01:47:28 2004 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 9594316A4CE; Tue, 17 Feb 2004 01:47:28 -0800 (PST) Received: from sarevok.idg.nl (ardvark.idg.nl [62.250.13.24]) by mx1.FreeBSD.org (Postfix) with ESMTP id 5B06243D1D; Tue, 17 Feb 2004 01:47:28 -0800 (PST) (envelope-from mdev@sarevok.idg.nl) Received: by sarevok.idg.nl (Postfix, from userid 100) id 144B9B922; Tue, 17 Feb 2004 10:47:26 +0100 (CET) From: Melvyn Sopacua Organization: WebTeckies.org To: current@FreeBSD.org Date: Tue, 17 Feb 2004 08:46:12 +0100 User-Agent: KMail/1.5.94 References: <12525.1076342049@critter.freebsd.dk> In-Reply-To: <12525.1076342049@critter.freebsd.dk> MIME-Version: 1.0 Content-Type: multipart/signed; protocol="application/pgp-signature"; micalg=pgp-sha1; boundary="Boundary-02=_JbcMA6XfkI7R/qm"; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <200402170846.17399.freebsd-current@webteckies.org> cc: Pawel Jakub Dawidek cc: Poul-Henning Kamp cc: drosih@rpi.edu cc: julian@elischer.org Subject: Re: Review/Test: Pseudo-device unit number management patch X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 17 Feb 2004 09:47:28 -0000 --Boundary-02=_JbcMA6XfkI7R/qm Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline On Monday 09 February 2004 16:54, Poul-Henning Kamp wrote: > In message <20040209150039.GS2803@pcwin002.win.tue.nl>, Stijn Hoop writes: > >On Mon, Feb 09, 2004 at 03:32:16PM +0100, Poul-Henning Kamp wrote: > >> Please also remember: /dev is _not_ an inventory of available devices. > > > >Just curious: what is it then? An inventory of available drivers? An > >inventory of open devices? > > "A naming-space gateway from filenames to device drivers > whose exact mapping is only stable in the timeinterval > between a successful open(2) and the corresponding close > (be it an explict close or not)." [2] > > Fortunately it is a good deal more deterministic than what my feeble > attempt at a definition above could make it sound :-) > > The practical effects are hard to explain, but one example is that > the stat/open race is much more fundamental in /dev than anywhere > else in the filesystem. > > In the normal filesystem, a few odd things may happen between calls > to stat(2) and open(2), in /proc you may get a different process > than you intended, but in /dev _any_ odd thing may happen. > > You thought you opened a serial port called /dev/foo connected to > your printer ? Well, I got news for you: it disappeared! How does this work, when there's no mechanism in place to signal "the retur= n=20 of the thingy". Mostly thinking about the keyboard here, because even if=20 there was a recheck_keyboard_existence utility, one couldn't really type it= =20 in. So far I haven't been able to plug-in the keyboard and get it back agai= n. This is also a problem with some kvm-switches (the more expensive ones seem= to=20 be able to fool the OS, but the ones you buy just for changing co-locaters= =20 don't). I haven't checked with PC-Weazle cards (VGA/mouse/keyboard=20 redirection to serial outlet for ia32/pci) and RELENG_5_x yet, but if these= =20 loose their keyboard as well, there's definitely a problem. =2D-=20 Melvyn =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D =46reeBSD sarevok.idg.nl 5.2-CURRENT FreeBSD 5.2-CURRENT #2: Mon Feb 16 19:= 59:52=20 CET 2004 =20 root@sarevok.webteckies.org:/usr/obj/usr/src/sys/SAREVOK_NOAPM_NODEBUG i386 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D --Boundary-02=_JbcMA6XfkI7R/qm Content-Type: application/pgp-signature Content-Description: signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.4 (FreeBSD) iD8DBQBAMcbJOv9JNmfFN5URAr51AJ9KsoNud/zJxi85kz5EzrfiCOvwUgCfYAYp kFxqg2MXDT4NbZvWV/BUkG8= =7RfQ -----END PGP SIGNATURE----- --Boundary-02=_JbcMA6XfkI7R/qm--