selectel / pyxs Goto Github PK

Trying to use this in order to interact with xenbus on a guest VM but keep running into an issue where I get the following:

UnexpectedPacket: _Packet(op=2, rq_id=66813, tx_id=0, size=360, payload='{}')

The code I am running is pretty straight forward as I am just trying to read the networking info from a particular mac address.

from pyxs.client import Router, Client
from pyxs.connection import XenBusConnection
router = Router(XenBusConnection())

with Client(router=router) as c:
    try:
        networking = c[b"vm-data/networking/BC764E20394F"]
        print(networking)
    except:
        pass

Is there something that I need to set that I am missing, or is it that this can only be run on the underlying host and not the guest vm.

Test code:

#!/usr/bin/python3

import pyxs

router = pyxs.Router(pyxs.connection.XenBusConnection())
xs = pyxs.Client(router=router)

try:
    xs.connect()
except pyxs.ConnectionError:
    print("ConnectionError caught")

Expected output on non-xen VM:

ConnectionError caught

Actual output on non-xen VM:

Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/share/python3.5/site-packages/pyxs/connection.py", line 199, in __init__
    self.fd = os.open(path, os.O_RDWR)
FileNotFoundError: [Errno 2] No such file or directory: '/proc/xen/xenbus'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/share/python3.5/threading.py", line 923, in _bootstrap_inner
    self.run()
  File "/usr/share/python3.5/threading.py", line 871, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/share/python3.5/site-packages/pyxs/client.py", line 101, in __call__
    self.connection.connect()
  File "/usr/share/python3.5/site-packages/pyxs/connection.py", line 52, in connect
    self.transport = self.create_transport()
  File "/usr/share/python3.5/site-packages/pyxs/connection.py", line 245, in create_transport
    return _XenBusTransport(self.path)
  File "/usr/share/python3.5/site-packages/pyxs/connection.py", line 202, in __init__
    .format(path, e.args))
pyxs.exceptions.ConnectionError: error while opening '/proc/xen/xenbus': (2, 'No such file or directory')

ConnectionError caught

Hi

Could you please update my email (in contributors) to sandeep DOT murthy AT icloud.com. Thanks.

Hi

At the moment there's no method to check whether a given path is a valid Xenstore path - would it be useful to add such a method to pyxs.helpers? A corresponding exception would be added to pyxs.exceptions. I am happy to do that, if you think this is useful.

SM

I'm integrating pyxs within a twisted base application.
I hit an issue where the select.select() call within Router.call was interrupted.
This call is within a try block without any except clause. It does not handle interrupted system calls within the select system call.
It seems that any error from select.select() would end up with a select.error exception which is not caught and the Router connection is terminated.
Is it right to catch such exception and re-issue the select.select() call?

The referenced AUTHORS file is missing and the BSD variant is not stated.
The copyright years are also missing for the named copyright holders.

The client.py currently contains a check for setting up a watch on xenstore:

https://github.com/selectel/pyxs/blob/master/pyxs/client.py#L619-L621

        if isinstance(self.router.connection, XenBusConnection):
            raise PyXSError("using ``Monitor`` over XenBus is not supported",
                            UserWarning)

This no longer seems to be a valid check with Xen 4.14.x + Linux 5.4 (Ubuntu kernel). I don't know whether the solution to the original problem was in Xen or Linux or with which versions that it started working. This code works in dom0 and domU with that check commented out:

#!/usr/bin/env python3

import sys
import threading
import time

import pyxs


class Watcher(threading.Thread):
    def __init__(self):
        super().__init__()
        self._monitor = None
        self._watch = b"/"
        self._token = b"token"
        self.start()


    def run(self):
        with pyxs.client.Client(xen_bus_path="/dev/xen/xenbus") as xsc:
            self._monitor = xsc.monitor()
            self._monitor.watch(self._watch, self._token)
            while self._monitor:
                print(next(self._monitor.wait(unwatched=True)))


    def stop(self):
        mtmp = self._monitor
        self._monitor = None
        # poke an event in queue for anything currently .wait()ing
        mtmp.events.put(pyxs.client.Event(self._watch, self._token)),


def main():
    watcher = Watcher()
    time.sleep(4)
    watcher.stop()
    watcher.join()


if __name__ == "__main__":
    sys.exit(
        main()
    )

It is possible to bypass the check by instantiating the Monitor() class directly with an existing Client().