Date: Wed, 19 Jul 2000 10:33:36 +0200 From: Adrian Chadd <adrian@freebsd.org> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: arch@freebsd.org Subject: Re: DEVFS, the complete picture (Was: Re: SysctlFS) Message-ID: <20000719103336.B40749@ywing.creative.net.au> In-Reply-To: <2732.963993497@critter.freebsd.dk>; from phk@critter.freebsd.dk on Wed, Jul 19, 2000 at 09:58:17AM %2B0200 References: <3974D642.59E2B600@elischer.org> <2732.963993497@critter.freebsd.dk>
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[To/CC list chomped because I think we're all on -arch anyway]
On Wed, Jul 19, 2000, Poul-Henning Kamp wrote:
> In message <3974D642.59E2B600@elischer.org>, Julian Elischer writes:
>
> >> Your "symlink device node" proposal still doesn't solve the
> >> cloning problem, so it is only 1/2 a solution to what in
> >> practice is a non-problem.
> >
> >It allows the cloning devices to be represented
> >all over the filesystems rather than limitted to the devfs,
> >thus it allows them to be in chroot/jails without zillions
> >of devfs mounts...
>
> No it doesn't. You "symlink" idea just replaces the major+minor
> with a string, that's all.
>
> Cloning can be done two ways, which I will illustrate with the pty
> driver as example:
>
> A) You open "/dev/pty", which clones and does some h0h0magic
> with vnodes and fdesc.
> You call ioctl(fd, WHATSMYREALNAME, buf, sizeof(buf))
> and it tells you that you are really "/dev/pty102".
>
> B) You try to open ("/dev/pty%d",N) for N [0...]
> Once an open succeeds you have your fd and your name.
> (this is what we do today)
The amount of h0h0magick needed for A from a vnode point of view
really isn't that much. In fact, if you wanted to make it less
evil you could mandate that stat.st_ino or even stat.st_dev reflects
the device minor number when you're cloning, which seems a lot neater
than the above ioctl().
(I used stat.st_ino when implementing the cloning creation file in my
inode FS FFS hack.)
2c,
adrian
--
Adrian Chadd Build a man a fire, and he's warm for the
<adrian@FreeBSD.org> rest of the evening. Set a man on fire and
he's warm for the rest of his life.
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