[HECnet] DECnet for Linux

[Erik Olofsen]

One more note:

In the last longterm 3.x.y kernel, 3.18.92, sock_alloc_send_skb()
sets the errcode to ENOBUFS even when the sk_buff is allocated
successfully. This causes sendmsg() to stop with "No buffer space
available". That is easy to fix in dn_alloc_send_pskb().


On Mon, Jan 15, 2018 at 09:43:53PM +0100, Erik Olofsen wrote:
> Some more notes on this:
> 
> The problem of accessing a Linux machine seems to be related to
> the standard mtu of 1500 of a network interface.
> 
> Reducing the maximum packet size to 576 helps;
> 
> https://sourceforge.net/p/linux-decnet/mailman/message/2395733/
> 
> This can be done using ifconfig or using 576 instead of dst_mtu()
> in dn_current_mss() af_decnet.c of the kernel module source.
> 
> tcpdump shows that a large data packet is one byte too long.
> Perhaps this occurs because the pad byte in the header is not counted
> in dn_mss_from_pmtu() in af_decnet.c; with an additional mtu--
> this seems to be fixed.
> 
> Kernel warnings related to dst.h;
> 
> https://www.spinics.net/lists/netdev/msg225996.html
> 
> indeed disappear by using dst_metric_raw at two places.
> 
> The above was tested with kernel 3.10.17, and can be tested
> with http://mim.update.uu.se/hecnet and nodename RULLFL.
> 
> dntype mim::nodenames.dat works very well on a real machine; why
> it doesn't work very well with the virtual machine is not really
> solved yet...
> 
> 
> On Wed, Jan 03, 2018 at 04:44:54PM +0100, Johnny Billquist wrote:
> > On 2018-01-03 16:02, Erik Olofsen wrote:
> > >On a virtual machine with lubuntu 12.04, kernel 3.2.0, I have
> > >DECnet for Linux V.2.5.68s working, with dnprogs version 2.65.
> > >It is node RULLFL.
> > >
> > >The daemons and utilities use decnet.conf with node information,
> > >so something useful would be to create it from mim::nodenames.dat.
> > >
> > >On a VAX, TYPEing it works well, but on the Linux machine, dntype
> > >hangs after giving parts of the file; dndir mim:: works well.
> > >
> > >Does anyone have dntype mim::nodenames.dat working properly (with
> > >perhaps different versions of the above)?
> > 
> > I can't help, but I can report that trying to read a file from a Linux
> > machine on MIM also hangs after a while.
> > A big problem with the DECnet/Linux implementation is that the developers
> > only ever tested against VMS, and nothing else.
> > 
> > I've known for ages that it does not play well with RSX. But I do not want
> > to dig into the Linux implementation.
> > 
> > (The Linux DAP claims to be a VMS system, by the way, which is probably also
> > not a good idea. Better if it had claimed to be some Unix derivative.)
> > 
> >   Johnny
> > 
> > -- 
> > Johnny Billquist                  || "I'm on a bus
> >                                   ||  on a psychedelic trip
> > email: bqt at softjar.se             ||  Reading murder books
> > pdp is alive!                     ||  tryin' to stay hip" - B. Idol