Date: Sat, 24 Jul 1999 04:40:29 +0100 From: Brian Somers <brian@Awfulhak.org> To: Alfred Perlstein <bright@rush.net> Cc: John-Mark Gurney <gurney_j@resnet.uoregon.edu>, Poul-Henning Kamp <phk@critter.freebsd.dk>, freebsd-bugs@FreeBSD.ORG Subject: Re: kern/12780: tun code panics when 0 bytes written (PATCH included) Message-ID: <199907240340.EAA05607@keep.lan.Awfulhak.org> In-Reply-To: Your message of "Fri, 23 Jul 1999 17:01:49 EDT." <Pine.BSF.3.96.990723165231.27774Q-100000@cygnus.rush.net>
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> On Fri, 23 Jul 1999, John-Mark Gurney wrote:
>
> > Poul-Henning Kamp scribbled this message on Jul 23:
> > > Zero length writes to a device are legal, at some point it was the
> > > way to write end of file and end of tape for magtapes: you would
> > > do one zero length write after each file and two at the end of the
> > > tape.
> >
> > yes, but this prevents tun from panicing BECAUSE of a zero length
> > write, this does not effect the device subsystem in any way... read
> > the code... the only other patch for this bug is to change the:
> > if (error) {
> > if (top) {
> >
> > to:
> > if (error || top) {
> >
> > and I decided that it was best to check and not try to allocate an mbuf
> > when we know we are just going to free it in a few lines of code..
> >
> > read the code and the patch...
>
> I think what Poul-Henning is saying is theat it may be improper to
> return EIO in this case, perhaps a successful return is warrented?
>
> this would also make ppp not complain about an error that it shouldn't
> get?
[.....]
I think the return should be either EINVAL or EMSGSIZE - EMSGSIZE is
now returned in OpenBSD (it's also returned for > MAX_MRU there).
IMHO it's invalid to write 0 bytes to this sort of device - it's
expecting a whole packet.
Also, ppp *should* complain. It didn't mean to write zero bytes -
it's a bug I introduced recently with my device layering changes
where IP fragments are mis-handled as zero length mbufs. It's now
fixed.
--
Brian <brian@Awfulhak.org> <brian@FreeBSD.org>
<http://www.Awfulhak.org>; <brian@OpenBSD.org>
Don't _EVER_ lose your sense of humour ! <brian@FreeBSD.org.uk>
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