[HECnet] DECnet for Linux Bug Fixes

[John Forecast]

> On Jun 30, 2020, at 10:29 AM, Gregg Levine <gregg.drwho8 at gmail.com> wrote:
> 
> Hello!
> Something else, all of my PI devices, from one from Seven years ago
> last December to one that arrived perhaps two years previously are all
> 32 bit devices, the build-it instructions presuppose that a lot of us
> own Pi4 devices who're 64 bit capable. That card image the both of us
> are interested in would need to work on both style systems.
> -----
> Gregg C Levine gregg.drwho8 at gmail.com
> "This signature fought the Time Wars, time and again."

Let me just say that almost all of my testing has been in 32-bit Raspbian on either a Pi Zero W or an original Pi 1B. If you ignore section 2.3 of Raspbian.README, the document describes how to install DECnet on a 32-bit system.

I’m not going to commit to building an image until I understand all of the ramifications. Since RPT is moving 2 versions of piOS (32 and 64-bit kernels and associated userland code), I would only consider building piOS images. Fortunately, the 64-bit PiOS has not been released yet so we’re really only talking about a single image.

Let me see how much work is involved.

  John.

> 
> On Tue, Jun 30, 2020 at 10:25 AM Gregg Levine <gregg.drwho8 at gmail.com> wrote:
>> 
>> Hello!
>> How about he's right? I do know I could sit down in front of an SSH
>> terminal screen to an appropriate device and use the git tool to
>> download the code and follow the instructions that should be inside
>> the README file. However there must be some of us out on the list who
>> can do that, but would rather use a previously constructed image for
>> the purpose.
>> -----
>> Gregg C Levine gregg.drwho8 at gmail.com
>> "This signature fought the Time Wars, time and again."
>> 
>> On Tue, Jun 30, 2020 at 10:12 AM Supratim Sanyal <supratim at riseup.net> wrote:
>>> 
>>> On 6/29/2020 20:45, John Forecast wrote:
>>> 
>>> Recently I have found, and fixed, a number of bugs in the DECnet for Linux kernel module. Some of
>>> these bugs may be relevant for members of this mailing list who are using DECnet for Linux,
>>> especially on a Raspberry Pi.
>>> 
>>> John - how about making our pandemic and politician-stressed lives a bit easier and uploading a microSD image somewhere relieving us from having to go through the hoops?
>>> 
>>> https://github.com/JohnForecast/RaspbianDECnet/blob/master/README.Raspbian is fantastic, BTW.
>>> 
>>> :)
>>> 
>>> Regards
>>> Supratim
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> Major bugs fixed:
>>> 
>>> - Ethernet Listen Timer was not implemented
>>> 
>>> In addition, the check for an address change for the designated router (DR) was missing
>>> although there was a check if the DR’s priority had changed.
>>> 
>>> Note: this code changes the format of /proc/net/decnet_dev to include the listen timer value.
>>>          nml/nml2 needs to be rebuilt to understand the changed format.
>>> 
>>> - System panic when using the loopback device (lo)
>>> 
>>> The DECnet code was missing a destructor routine which is used to avoid data copying.
>>> 
>>> - The neighbour (adjacent node) code could be broken by kernel changes
>>> 
>>> The code made use of a now deprecated feature (zero length array at the end of a structure)
>>> in order to access data in a surrounding structure. This happened to work “by chance”
>>> until kernel 5.4.42 on 32-bit processors.
>>> 
>>> - Interrupt message flow control was broken
>>> 
>>> The flow control was a mixture of using the SEND/DONTSEND status of the data
>>> subchannel and a message count. This seems to work between Linux systems but is broken
>>> when communicating with other systems - during the life of a logical link, the remote system
>>> could only send a single interrupt message while the Linux system could pretty much send
>>> as many interrupts as it wanted possibly overrunning the remote systems buffers.
>>> 
>>> - Optional data on received connect confirm message was corrupted
>>> 
>>> The code was getting the optional data from the wrong offset in the message.
>>> 
>>> - Next hop cache problem
>>> 
>>> 30 seconds after a logical link was taken down, the next hop cache entry was deleted. As
>>> part of this deletion, the link was taken “down” which caused a neighbour entry to be
>>> created for the same node address but accessed via the loopback device. Sometimes this
>>> would cause the designated router to become accessible via the loopback device and
>>> subsequent connections would fail.
>>> 
>>> - Intra-ethernet bit ignored
>>> 
>>> The intra-ethernet bit in the routing flags is ignored on inbound traffic. If there was a neighbour
>>> entry for the remote node at connection time, everything would work correctly. If there wad no
>>> entry, all outbound  traffic would be sent through the designated router for the duration of
>>> the logical link.
>>> 
>>> - Promiscuous mode alters DECnet behaviour
>>> 
>>> If the ethernet NIC used for DECnet had promiscuous mode enabled (e.g. using tcpdump
>>> for traffic tracing), the DECnet code would start seeing endnode hello’s, populating
>>> neighbour structures and causing the problems described above for the intra-ethernet bit
>>> to go away.
>>> 
>>> New programs:
>>> 
>>> DECnet Test Send and DECnet Test Receiver (DTS/DTR)
>>> 
>>> Test programs created via reverse engineering the protocol exchanges. Used to find a
>>> number of the bugs described above.
>>> 
>>> NML2
>>> 
>>> New implementation of the Network Management Listener. Supports SUMMARY, STATUS
>>> and CHARACTERISTICS for NODES, CIRCUITS and AREAS. It does not support LINKS
>>> and OBJECTS which were in the old version but are system specific operations which
>>> were only visible from DECnet-VMS systems.
>>> 
>>> The old version is still the default during installation. The new version can be installed by:
>>> 
>>> cd dnprogs/nml2
>>> make
>>> sudo make install
>>> 
>>> which will overwrite the installed executable and man page.
>>> 
>>> OS Support:
>>> 
>>> As of 06/29/2020 the code has been tested with:
>>> 
>>> Raspbian 2020-05-27 release with kernels 4.19.126 and 5.4.44 (32-bit only)
>>> 
>>> Pi OS 2020-05-27 32-bit release with kernel 4.19.126 and 5.4.44
>>> 
>>> pI OS 2020-05-27 (fully updated on 06/26/2020) with kernel 5.4.49
>>> 
>>> 
>>> The source code and installation instructions are available at:
>>> 
>>> <https://github.com/JohnForecast/RaspbianDECnet>
>>> 
>>>  John.
>>> 
>>> --
>>> Supratim Sanyal, W1XMT
>>> 39.19151 N, 77.23432 W
>>> QCOCAL::SANYAL via HECnet