Re: Interface auto-cloning bug or feature?

On 9/19/08, Maxim Sobolev <sobomax_at_freebsd.org> wrote:
> Maksim Yevmenkin wrote:
>
> > On 9/19/08, Ed Schouten <ed_at_80386.nl> wrote:
> >
> > > Hello Maxim,
> > >
> > >
> > >  * Maxim Sobolev <sobomax_at_FreeBSD.org> wrote:
> > >  > I've noticed that stat/open call on /dev/tun always creates new
> > >  > interface, despite the fact that existing spare interfaces may be
> > >  > available. I believe that it's a bug, since the whole purpose of
> > >  > auto-cloning is to create new instance only when no existing one
> could
> > >  > be allocated. At least that's my reading of the manual page for the
> tun(4).
> > >
> > >
> > > I'd say the best way to fix this would be to convert tun and tap to
> > >  devfs_[gs]et_cdevpriv() and turn tun and tap into single device nodes.
> > >  That's what we've already been doing to bpf, snp, audit_pipe, etc.
> > >  Unfortunately I'm no expert when it comes to our tun and tap
> > >  implementations.
> > >
> >
> > not so fast please :) the tap/tun/vkbd (and maybe others) have split
> > personality. that is, on one side there is a network interface or
> > keyboard, and on the other side is character device. those are always
> > go in pairs. as far as i understand, of
> > dev_stdclone/clone_create/clonedevs list/etc. is here to
> free up
> > driver from managing resources (such as minor numbers). sure we can
> > convert those drivers to devfs_set/get_cdevpriv, however, split
> > personality drivers will still have to manage something similar to
> > minor numbers (to name network interfaces/keyboards associated with
> > the particular cdevpriv instance). also we need to make sure that any
> > code still could use /dev/tunX/tapX names and get correct tunX/tapX
> > interface (provided, of course, one is available).
> >
>
>  Why opening /dev/tun can't search and return the first unopened instance
> (as the manpage suggests it would) instead of unconditionally allocating a
> new one? Seems to me like a trivial change, most of the code is already
> there.

why indeed :) i'll try to hack something up in the next couple of
hours or so. stay tuned.

thanks,
max

>
>  -Maxim
>