WIP : Extended ack support

[ffourcot]

Hello Peter,

During some debug with kernel netlink messages, it appears to us that extended ack support could be a great feature in pyroute2, allowing to read more useful error messages.

I wrote in this MR a proof of concept of how it's working, that one can reproduce with :

In [1]: from pyroute2 import IPRoute

In [2]: ipr = IPRoute(ext_ack=True)

In [3]: ipr.link("dump", if_netnsid=4)  # here 4 must be an invalid netns number
{'error': -22, 'attrs': [('NLMSGERR_ATTR_MSG', 'Invalid target network namespace id')], 'header': {'length': 60, 'type': 3, 'flags': 514, 'sequence_number': 255, 'pid': 30621}}

However, there are still a lot of work before to be able to merge it. I didn't find a good way to parse standard nlmsg as nlmsgerr when NLM_F_ACK_TLVS flah is set.

And there are a lot of missing feature, like capped messages, cookies, etc. But I have currently no idea of the best idea to go forward. Could you have a look on it?

[svinota]

Great! Thanks a lot, looking

[ffourcot]

Hello @svinota, any news on this topic? I didn't had the time to investigate until now, but I still think that this feature could be great in pyroute2. Any advice to move forward?

Thanks

[svinota]

Didn't have time either, but I believe the project must have this feature.

Let me play a bit over this weekend and I'll merge it in this or other way.

[svinota]

Why don't you think it's a proper place to parse an error message?

[ffourcot]

In my opinion, this should be in msg.decode() itself, if possible. It looks weird for me to call msg.decode() twice

And it's not only about error parsing. I hardcoded the nlmsgerr class here, but we can receive some "cookies" with relevant data when extack is enabled

[svinota]

The change looks quite simple, I'm for it

[svinota]

Looks like I don't understand something, but can not get it working.

@ffourcot , could you please provide a testcase that would run on net-next 5.11+?

[ffourcot]

Hello @svinota,

Yes! I will take some times to provide two scripts (one returning one error, and one with cookies)

[svinota]

Got it working, thus I can proceed now with implementation.

Regarding extra decoding — I'll look if it may be done more properly.

[svinota]

@ffourcot I plan to raise an exception on nlmsgerr() as it's done on ordinary errors.

Any objections / comments ?

(venv) {ffourcot-extended_ack} $ cat e55.py 
from pyroute2 import IPRoute
with IPRoute(ext_ack=True) as ipr:
    ipr.link('dump', if_netnsid=4)

(venv) {ffourcot-extended_ack} $ python e55.py 
Traceback (most recent call last):
  File "/home/test/Projects/pyroute2/e55.py", line 4, in <module>
    ipr.link('dump', if_netnsid=4)
  File "/home/test/Projects/pyroute2/pyroute2/iproute/linux.py", line 1378, in link
    ret = self.nlm_request(msg,
  File "/home/test/Projects/pyroute2/pyroute2/netlink/nlsocket.py", line 390, in nlm_request
    return tuple(self._genlm_request(*argv, **kwarg))
  File "/home/test/Projects/pyroute2/pyroute2/netlink/nlsocket.py", line 881, in nlm_request
    for msg in self.get(msg_seq=msg_seq,
  File "/home/test/Projects/pyroute2/pyroute2/netlink/nlsocket.py", line 393, in get
    return tuple(self._genlm_get(*argv, **kwarg))
  File "/home/test/Projects/pyroute2/pyroute2/netlink/nlsocket.py", line 718, in get
    raise msg['header']['error']
pyroute2.netlink.exceptions.NetlinkError: (-22, 'Invalid target network namespace id')

[ffourcot]

Got it working, thus I can proceed now with implementation.

Great! Thank you

@ffourcot I plan to raise an exception on nlmsgerr() as it's done on ordinary errors.

It's perfect from my point of view. The real message from kernel code will really help

[svinota]

Merged manually.

The condition to raise the exception is NLMSG_DONE + NLM_F_ACK_TLVS + msg['error'], sinceNLM_F_ACK_TLVS may happen in other dumps as well but w/o any error attached.

Please review the functionality and don't hesitate to open tickets and PR:s.