Date: Tue, 17 Feb 2004 08:46:12 +0100 From: Melvyn Sopacua <freebsd-current@webteckies.org> To: current@FreeBSD.org Cc: julian@elischer.org Subject: Re: Review/Test: Pseudo-device unit number management patch Message-ID: <200402170846.17399.freebsd-current@webteckies.org> In-Reply-To: <12525.1076342049@critter.freebsd.dk> References: <12525.1076342049@critter.freebsd.dk>
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--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--
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