Date: Thu, 17 May 2001 12:19:22 -0700 From: Peter Wemm <peter@wemm.org> To: Brian Somers <brian@Awfulhak.org> Cc: Poul-Henning Kamp <phk@critter.freebsd.dk>, cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/fs/devfs devfs_vnops.c Message-ID: <20010517191922.B6C4D380A@overcee.netplex.com.au> In-Reply-To: <200105171258.f4HCwKb63116@hak.lan.Awfulhak.org>
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Brian Somers wrote:
> > >> Revision Changes Path
> > >> 1.23 +7 -15 src/sys/fs/devfs/devfs_vnops.c
> > >
> > >Does this mean that I can catch ``open("/dev/tun")'' and clone (say)
> > >/dev/tun100, returning that ?
> >
> > yes :-)
>
> I think the only thing that's missing is that you can't have the
> clone handler called for an existing device node.
>
> I'd like to be able to make_dev() /dev/tun during attach and allow
> the sysadmin (or whatever) to change it's permissions. Then, when an
> attempt to open it is made, have my clone handler called. My clone
> handler make_dev()s /dev/tunN and returns that. When /dev/tunN's
> final close is done, I destroy_dev() it.
>
> Unfortunately, I don't think this can be done very easily. We'd need
> to allocate a new vnode only at open time - probably in vn_open.
> It'd probably be convenient if devfs was able to set some new vnode
> flag in vnodes returned from it's lookup based on some flag passed
> into make_dev() (oops, there are no flags there). When vn_open()
> sees the flag, it calls some registered handler that goes off and
> returns either the original vnode or (if successfully cloned) a new
> vnode.
>
> Does any of that make sense ?
It does make sense, but are you sure it's needed? The clone device (/dev/
tun in this case) has the same attributes as the redirected device. Ie: if
you open /dev/tun, the attributes of it are actually those of /dev/tun100.
I dont think we can have a persistant /dev/tun that actually shows up on
ls(1) etc, because we'd then have races with multiple processes scanning/
accessing the directories or accessing and opening by different processes
at once. Remember, the cloned device is different to every process.
The whole permissions thing is a sticky one there.
Cheers,
-Peter
--
Peter Wemm - peter@FreeBSD.org; peter@yahoo-inc.com; peter@netplex.com.au
"All of this is for nothing if we don't go to the stars" - JMS/B5
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