Re: Review/Test: Pseudo-device unit number management patch

From: Melvyn Sopacua (freebsd-current_at_webteckies.org)
Date: 02/17/04

  • Next message: Russell Jackson: "Re: msdthdat.c revision 1.1.1.21 breaks cardbus" 
    To: current@FreeBSD.org
Date: Tue, 17 Feb 2004 08:46:12 +0100

    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 return
    of the thingy". Mostly thinking about the keyboard here, because even if
    there was a recheck_keyboard_existence utility, one couldn't really type it
    in. So far I haven't been able to plug-in the keyboard and get it back again.

    This is also a problem with some kvm-switches (the more expensive ones seem to
    be able to fool the OS, but the ones you buy just for changing co-locaters
    don't). I haven't checked with PC-Weazle cards (VGA/mouse/keyboard
    redirection to serial outlet for ia32/pci) and RELENG_5_x yet, but if these
    loose their keyboard as well, there's definitely a problem. 

    -- 
Melvyn
=======================================================
FreeBSD sarevok.idg.nl 5.2-CURRENT FreeBSD 5.2-CURRENT #2: Mon Feb 16 19:59:52 
CET 2004     
root@sarevok.webteckies.org:/usr/obj/usr/src/sys/SAREVOK_NOAPM_NODEBUG  i386
=======================================================

    • application/pgp-signature attachment: signature
  • Next message: Russell Jackson: "Re: msdthdat.c revision 1.1.1.21 breaks cardbus"