Scriptable KVM/QEMU guest agent implemented in Python

Welcome to the documentation of negotiator version 0.12.2! The following sections are available:

User documentation

The readme is the best place to start reading, it’s targeted at all users and documents the command line interface:

Scriptable KVM/QEMU guest agent implemented in Python

The Python packages negotiator-host, negotiator-guest and negotiator-common together implement a scriptable KVM/QEMU guest agent infrastructure in Python. This infrastructure supports realtime bidirectional communication between Linux hosts and guests which allows the hosts and guests to invoke user defined commands on ‘the other side’.

Because the user defines the commands that hosts and guests can execute, the user controls the amount of influence that hosts and guests have over each other (there are several built-in commands, these are all read only).

Status

Some points to consider:

  • The Negotiator project does what I expect from it: realtime bidirectional communication between Linux based KVM/QEMU hosts and guests.
  • The project doesn’t have an automated test suite, although its functionality has been extensively tested during development and is being used in a production environment on more than 100 virtual machines (for non-critical tasks).
  • The project has not been peer reviewed with regards to security. My primary use case is KVM/QEMU hosts and guests that trust each other to some extent (think private clouds, not shared hosting :-).

Installation

The negotiator packages and their dependencies are compatible with Python 2.7 and newer and are all pure Python. This means you don’t need a compiler toolchain to install the negotiator packages. This is a design decision and so won’t be changed.

On KVM/QEMU hosts

Here’s how to install the negotiator-host package on your host(s):

$ sudo pip install negotiator-host

If you prefer you can install the Python package in a virtual environment:

$ sudo apt-get install --yes python-virtualenv
$ virtualenv /tmp/negotiator-host
$ source /tmp/negotiator-host/bin/activate
$ pip install negotiator-host

After installation the negotiator-host program is available. The usage message will help you get started, try the --help option. Now you need to find a way to run the negotiator-host command as a daemon. I have good experiences with supervisord, here’s how to set that up:

$ sudo apt-get install --yes supervisor
$ sudo tee /etc/supervisor/conf.d/negotiator-host.conf >/dev/null << EOF
[program:negotiator-host]
command = /usr/local/bin/negotiator-host --daemon
autostart = True
stdout_logfile = /var/log/negotiator-host.log
stderr_logfile = /var/log/negotiator-host.log
EOF
$ sudo supervisorctl update negotiator-host
On KVM/QEMU guests

Install the negotiator-guest package on your guest(s):

$ sudo pip install negotiator-guest

If you prefer you can install the Python package in a virtual environment:

$ sudo apt-get install --yes python-virtualenv
$ virtualenv /tmp/negotiator-guest
$ source /tmp/negotiator-guest/bin/activate
$ pip install negotiator-guest

After installation you need to find a way to run the negotiator-guest command as a daemon. I have good experiences with supervisord, here’s how to set that up:

$ sudo apt-get install --yes supervisor
$ sudo tee /etc/supervisor/conf.d/negotiator-guest.conf >/dev/null << EOF
[program:negotiator-guest]
command = /usr/local/bin/negotiator-guest --daemon
autostart = True
stdout_logfile = /var/log/negotiator-guest.log
stderr_logfile = /var/log/negotiator-guest.log
EOF
$ sudo supervisorctl update negotiator-guest

Getting started

If the instructions below are not enough to get you started, take a look at the Debugging section below for hints about what to do when things don’t work as expected.

  1. First you have to add two virtual devices to your QEMU guest. You can do so by editing the guest’s XML definition file. On Ubuntu Linux KVM/QEMU hosts these files are found in the directory /etc/libvirt/qemu. Open the file in your favorite text editor (Vim? :-) and add the the following XML snippet inside the <devices> section:

    <channel type='unix'>
   <source mode='bind' path='/var/lib/libvirt/qemu/channel/target/GUEST_NAME.negotiator-host-to-guest.0' />
   <target type='virtio' name='negotiator-host-to-guest.0' />
</channel>

<channel type='unix'>
   <source mode='bind' path='/var/lib/libvirt/qemu/channel/target/GUEST_NAME.negotiator-guest-to-host.0' />
   <target type='virtio' name='negotiator-guest-to-host.0' />
</channel>

    Replace GUEST_NAME with the name of your guest in both places. If you use libvirt 1.0.6 or newer (you can check with virsh --version) you can omit the path='...' attribute because libvirt will fill it in automatically when it reloads the guest’s XML definition file (in step 2).

  2. After adding the configuration snippet you have to activate it:

    $ sudo virsh define /etc/libvirt/qemu/GUEST_NAME.xml

  3. Now you need to shut down the guest and then start it again:

    $ sudo virsh shutdown --mode acpi GUEST_NAME
$ sudo virsh start GUEST_NAME

    Note that just rebooting the guest will not add the new virtual devices, you have to actually stop the guest and then start it again!

  4. Now go and create some scripts in /usr/lib/negotiator/commands and try to execute them from the other side! Once you start writing your own commands it’s useful to know that commands on the KVM/QEMU host side have access to some environment variables.

Usage

This section documents the command line interfaces of the programs running on hosts and guests. For information on the Python API please refer to the online documentation on Read the Docs.

The negotiator-host program

Usage: negotiator-host [OPTIONS] GUEST_NAME

Communicate from a KVM/QEMU host system with running guest systems using a guest agent daemon running inside the guests.

Supported options:

Option Description
-g, --list-guests List the names of the guests that have the appropriate channel.
-c, --list-commands List the commands that the guest exposes to its host.
-e, --execute=COMMAND Execute the given command inside GUEST_NAME. The standard output stream of the command inside the guest is intercepted and copied to the standard output stream on the host. If the command exits with a nonzero status code the negotiator-host program will also exit with a nonzero status code.
-t, --timeout=SECONDS Set the number of seconds before a remote call without a response times out. A value of zero disables the timeout (in this case the command can hang indefinitely). The default is 10 seconds.
-d, --daemon Start the host daemon that answers real time requests from guests.
-v, --verbose Increase logging verbosity (can be repeated).
-q, --quiet Decrease logging verbosity (can be repeated).
-h, --help Show this message and exit.
The negotiator-guest program

Usage: negotiator-guest [OPTIONS]

Communicate from a KVM/QEMU guest system to its host or start the guest daemon to allow the host to execute commands on its guests.

Supported options:

Option Description
-l, --list-commands List the commands that the host exposes to its guests.
-e, --execute=COMMAND Execute the given command on the KVM/QEMU host. The standard output stream of the command on the host is intercepted and copied to the standard output stream on the guest. If the command exits with a nonzero status code the negotiator-guest program will also exit with a nonzero status code.
-d, --daemon Start the guest daemon. When using this command line option the “negotiator-guest” program never returns (unless an unexpected error condition occurs).
-t, --timeout=SECONDS Set the number of seconds before a remote call without a response times out. A value of zero disables the timeout (in this case the command can hang indefinitely). The default is 10 seconds.
-c, --character-device=PATH By default the appropriate character device is automatically selected based on /sys/class/virtio-ports/*/name. If the automatic selection doesn’t work, you can set the absolute pathname of the character device that’s used to communicate with the negotiator-host daemon running on the KVM/QEMU host.
-v, --verbose Increase logging verbosity (can be repeated).
-q, --quiet Decrease logging verbosity (can be repeated).
-h, --help Show this message and exit.

Debugging

This section contains hints about what to do when things don’t work as expected.

Broken channels on KVM/QEMU hosts

Whether you want to get the official QEMU guest agent or the Negotiator project running, you will need a working bidirectional channel. I’m testing Negotiator on an Ubuntu 14.04 KVM/QEMU host and I needed several changes to get things working properly:

$ CHANNELS_DIRECTORY=/var/lib/libvirt/qemu/channel/target
$ sudo mkdir -p $CHANNELS_DIRECTORY
$ sudo chown libvirt-qemu:kvm $CHANNELS_DIRECTORY

The above should be done by the KVM/QEMU system packages if you ask me, but anyway. On top of this if you are running Ubuntu with AppArmor enabled (the default) you may need to apply the following patch:

$ diff -u /etc/apparmor.d/abstractions/libvirt-qemu.orig /etc/apparmor.d/abstractions/libvirt-qemu
--- /etc/apparmor.d/abstractions/libvirt-qemu.orig      2015-09-19 12:46:54.316593334 +0200
+++ /etc/apparmor.d/abstractions/libvirt-qemu   2015-09-24 14:43:43.642064576 +0200
@@ -49,6 +49,9 @@
   /run/shm/ r,
   owner /run/shm/spice.* rw,

+  # Local modification to enable the QEMU guest agent.
+  owner /var/lib/libvirt/qemu/channel/target/* rw,
+
   # 'kill' is not required for sound and is a security risk. Do not enable
   # unless you absolutely need it.
   deny capability kill,

Again this should just be part of the KVM/QEMU system packages, but whatever. The Negotiator project is playing with new-ish functionality so I pretty much know to expect sharp edges :-)

Character device detection fails

When the negotiator-guest program fails to detect the correct character devices it will complain loudly and point you here. Here are some of things I’ve run into that can cause this:

  • The virtual channel(s) have not been correctly configured or the correct configuration hasn’t been applied yet. Please carefully follow the instructions in the Getting started section above.
  • The kernel module virtio_console is not loaded because it is not available in your kernel. You can check by using the lsmod command. If the module is not loaded you’ll need to install and boot to a kernel that does have the module.

Why another guest agent?

The QEMU project provides an official guest agent and this agent is very useful to increase integration between QEMU hosts and guests. However the official QEMU guest agent has two notable shortcomings (for me at least):

Extensibility
The official QEMU guest agent has some generic mechanisms like being able to write files inside guests, but this is a far cry from a generic, extensible architecture. Ideally given the host and guest’s permission we should be able to transfer arbitrary data and execute user defined logic on both sides.
Platform support
Despite considerable effort I haven’t been able to get a recent version of the QEMU guest agent running on older Linux distributions (e.g. Ubuntu Linux 10.04). Older versions of the guest agent can be succesfully compiled for such distributions but don’t support the features I require. By creating my own guest agent I have more control over platform support (given the primitives required for communication).

Note that my project in no way tries to replace the official QEMU guest agent. For example I have no intention of implementing freezing and thawing of file systems because the official agent already does that just fine :-). In other words the two projects share a lot of ideas but have very different goals.

How does it work?

The scriptable guest agent infrastructure uses the same mechanism that the official QEMU guest agent does:

  • Inside the guest special character devices are created that allow reading and writing. These character devices are /dev/vport[0-9]p[0-9].
  • On the host UNIX domain sockets are created that are connected to the character devices inside the guest. On Ubuntu Linux KVM/QEMU hosts, these UNIX domain sockets are created in the directory /var/lib/libvirt/qemu/channel/target.

Contact

The latest version of negotiator is available on PyPI and GitHub. You can find the documentation on Read The Docs. For bug reports please create an issue on GitHub. If you have questions, suggestions, etc. feel free to send me an e-mail at peter@peterodding.com.

License

This software is licensed under the MIT license.

© 2019 Peter Odding.

API documentation

The following API documentation is automatically generated from the source code:

API documentation

The following documentation is based on the source code of version 0.12.2 of the negotiator project:

negotiator_host

Channel for communication with guests.

This module implements the GuestChannel class which provides the host side of the channel between QEMU hosts and guests. Channel objects can be used to query and command running guests.

class negotiator_host.AutomaticGuestChannel(guest_name, unix_socket)

Thin wrapper for GuestChannel that puts it in a separate process.

Uses multiprocessing.Process to isolate guest channels in separate processes.

__init__(guest_name, unix_socket)

Initialize a GuestChannel in a separate process.

Parameters:
  • guest_name – The name of the guest to connect to (a string).
  • unix_socket – The absolute pathname of the UNIX socket that we should connect to (a string).
run()

Start the main loop of the common negotiator interface.

class negotiator_host.GuestChannel(guest_name, unix_socket=None)

The host side of the channel connecting KVM/QEMU hosts and guests.

See also AutomaticGuestChannel which wraps GuestChannel and puts it in its own process.

__init__(guest_name, unix_socket=None)

Initialize a negotiator host agent.

Parameters:
  • guest_name – The name of the guest to connect to (a string).
  • unix_socket – The absolute pathname of the UNIX socket that we should connect to (a string, optional).
prepare_environment()

Prepare environment variables for command execution on KVM/QEMU hosts.

The following environment variables are currently exposed to commands:

$NEGOTIATOR_GUEST
The name of the KVM/QEMU guest that invoked the command.
exception negotiator_host.GuestChannelInitializationError

Exception raised by GuestChannel when socket initialization fails.

exception negotiator_host.GuestDiscoveryError

Exception raised by find_running_guests() when virsh list fails.

class negotiator_host.HostDaemon

The host daemon automatically manages a group of processes that handle “guest to host” calls.

__init__()

Initialize the host daemon.

cleanup_workers(running_guests)

Cleanup crashed workers and workers for guests that are no longer running.

enter_main_loop()

Create and maintain active channels for all running guests.

spawn_workers(running_guests)

Spawn new workers on demand (ignoring guests known not to support negotiator).

update_workers()

Automatically spawn subprocesses (workers) to maintain connections to all guests.

negotiator_host.find_channels_of_guest(guest_name)

Find the pathnames of the channels associated to a guest.

Parameters:guest_name – The name of the guest (a string).
Returns:A dictionary with channel names (strings) as keys and pathnames of UNIX socket files (strings) as values. If no channels are detected an empty dictionary will be returned.

This function uses virsh dumpxml and parses the XML output to determine the pathnames of the channels associated to the guest.

negotiator_host.find_running_guests()

Find the names of the guests running on the current host.

This function parses the output of the virsh list command instead of using the libvirt API because of two reasons:

  1. I’m under the impression that the libvirt API is still very much in flux and large changes are still being made, so it’s not the most stable foundation for Negotiator to find running guests.
  2. The Python libvirt API needs to match the version of the libvirt API on the host system and there is AFAIK no obvious way to express this in the setup.py script of Negotiator.
Returns:A generator of strings.
Raises:GuestDiscoveryError when virsh list fails.
negotiator_host.find_supported_guests()

Find guests supporting the negotiator interface.

Returns:A generator of strings with guest names.

This function uses find_running_guests() to determine which guests are currently running and then uses find_channels_of_guest() to determine which guests support the negotiator interface.

negotiator_host.cli

Usage: negotiator-host [OPTIONS] GUEST_NAME

Communicate from a KVM/QEMU host system with running guest systems using a guest agent daemon running inside the guests.

Supported options:

Option Description
-g, --list-guests List the names of the guests that have the appropriate channel.
-c, --list-commands List the commands that the guest exposes to its host.
-e, --execute=COMMAND Execute the given command inside GUEST_NAME. The standard output stream of the command inside the guest is intercepted and copied to the standard output stream on the host. If the command exits with a nonzero status code the negotiator-host program will also exit with a nonzero status code.
-t, --timeout=SECONDS Set the number of seconds before a remote call without a response times out. A value of zero disables the timeout (in this case the command can hang indefinitely). The default is 10 seconds.
-d, --daemon Start the host daemon that answers real time requests from guests.
-v, --verbose Increase logging verbosity (can be repeated).
-q, --quiet Decrease logging verbosity (can be repeated).
-h, --help Show this message and exit.
class negotiator_host.cli.Context

Enables main() to inject a custom timeout into partially applied actions.

__init__()

Initialize a context for executing commands on the host.

execute_command(guest_name, command_line)

Execute a command inside the named guest.

print_commands(guest_name)

Print the commands supported by the guest.

print_guest_names()

Print the names of the guests that Negotiator can connect with.

negotiator_host.cli.main()

Command line interface for the negotiator-host program.

negotiator_guest

The guest agent daemon and client.

This module implements the guest agent, the Python daemon process that’s always running inside KVM/QEMU guests.

class negotiator_guest.GuestAgent(character_device, retry=False)

Implementation of the daemon running inside KVM/QEMU guests.

__init__(character_device, retry=False)

Initialize a negotiator guest agent.

Parameters:
  • character_device – The absolute pathname of the character device that we should use to connect to the host (a string).
  • retry – True to retry EBUSY errors, False otherwise (defaults to False).

Note

When retry is True it is (somewhat theoretically) possible for infinite retrying to cause control to never be returned to the caller. This is why callers are expected to use TimeOut or a similar solution.

raw_readline()

Read a newline terminated string from the remote side.

This method overrides the raw_readline() method of the NegotiatorInterface() class to implement blocking reads based on os.O_ASYNC and signal.SIGIO (see also WaitForRead).

Returns:The data read from the remote side (a string).
retry_open(character_device, mode)

Open the character device and retry EBUSY errors.

class negotiator_guest.WaitForRead(group=None, target=None, name=None, args=(), kwargs={})

Used by GuestAgent.raw_readline() to implement blocking reads.

run()

Endless loop that waits for one or more SIGIO signals to arrive.

signal_handler(signal_number, frame)

Signal handler for SIGIO signals that immediately exits the process.

negotiator_guest.find_character_device(port_name)

Find the character device for the given port name.

Parameters:port_name – The name of the virtio port (a string).
Returns:The absolute pathname of a character device (a string).
Raises:Exception when the character device cannot be found.

negotiator_guest.cli

Usage: negotiator-guest [OPTIONS]

Communicate from a KVM/QEMU guest system to its host or start the guest daemon to allow the host to execute commands on its guests.

Supported options:

Option Description
-l, --list-commands List the commands that the host exposes to its guests.
-e, --execute=COMMAND Execute the given command on the KVM/QEMU host. The standard output stream of the command on the host is intercepted and copied to the standard output stream on the guest. If the command exits with a nonzero status code the negotiator-guest program will also exit with a nonzero status code.
-d, --daemon Start the guest daemon. When using this command line option the “negotiator-guest” program never returns (unless an unexpected error condition occurs).
-t, --timeout=SECONDS Set the number of seconds before a remote call without a response times out. A value of zero disables the timeout (in this case the command can hang indefinitely). The default is 10 seconds.
-c, --character-device=PATH By default the appropriate character device is automatically selected based on /sys/class/virtio-ports/*/name. If the automatic selection doesn’t work, you can set the absolute pathname of the character device that’s used to communicate with the negotiator-host daemon running on the KVM/QEMU host.
-v, --verbose Increase logging verbosity (can be repeated).
-q, --quiet Decrease logging verbosity (can be repeated).
-h, --help Show this message and exit.
negotiator_guest.cli.main()

Command line interface for the negotiator-guest program.

negotiator_common

Common shared functionality between the negotiator host and guest.

This Python module contains the functionality that is shared between the negotiator-host and negotiator-guest packages. By moving all of the shared functionality to a separate Python package and using Python package dependencies to pull in the negotiator-common package we stimulate code reuse while avoiding code duplication.

class negotiator_common.NegotiatorInterface(handle, label)

Common logic shared between the host/guest components.

This class defines the protocol that’s used to communicate between the Python programs running on the hosts and guests.

__init__(handle, label)

Initialize a negotiator host or guest agent.

Parameters:
  • handle – A file like object connected to the other side.
  • label – A string describing the file like object (used in logging).

This constructor is intended to be called by sub classes to provide the base class with the context it needs to set up bidirectional communication between the host and guest agents.

call_remote_method(method, *args, **kw)

Call a method on the remote object.

Parameters:
  • method – The name of the method to call (a string).
  • args – The positional arguments for the method.
  • kw – The keyword arguments for the method.
Returns:

The return value of the remote method.
enter_main_loop()

Wait for requests from the other side.

The communication protocol for remote procedure calls is as follows:

  • Every request is a dictionary containing at least a command key with a string value (the name of the method to invoke).
  • The value of the optional arguments key gives a list of positional arguments to pass to the method.
  • The value of the optional keyword-arguments key gives a dictionary of keyword arguments to pass to the method.

Responses are structured as follows:

  • Every response is a dictionary containing at least a success key with a boolean value.
  • If success=True the key result gives the return value of the method.
  • If success=False the key error gives a string explaining what went wrong.
Raises:ProtocolError when the remote side violates the defined protocol.
execute(*command, **options)

Execute a user defined or built-in command.

Parameters:
  • command – The command name and any arguments (one or more strings).
  • input – The input to feed to the command on its standard input stream (a string or None).
Returns:

The output of the command (a string) or None if the command exited with a nonzero exit code.
list_commands()

Find the names of the user defined commands.

Returns:A list of executable names (strings).
prepare_environment()

Prepare environment variables for command execution.

This method can be overridden by sub classes to prepare environment variables for external command execution.

raw_read(num_bytes)

Read the given number of bytes from the remote side.

Parameters:num_bytes – The number of bytes to read (an integer).
Returns:The data read from the remote side (a string).
raw_readline()

Read a newline terminated string from the remote side.

Returns:The data read from the remote side (a string).
raw_write(data)

Write a string of data to the remote side.

Parameters:data – The data to write tot the remote side (a string).
read()

Wait for a JSON encoded message from the remote side.

The basic communication protocol is really simple:

  1. First an ASCII encoded integer number is received, terminated by a newline.
  2. Second the number of bytes given by step 1 is read and interpreted as a JSON encoded value. This step is not terminated by a newline.

That’s it :-).

Returns:The JSON value decoded to a Python value.
Raises:ProtocolError when the remote side violates the defined protocol.
write(value)

Send a Python value to the other side.

Parameters:value – Any Python value that can be encoded as JSON.
exception negotiator_common.ProtocolError

Exception that is raised when the communication protocol is violated.

exception negotiator_common.RemoteMethodFailed

Exception that is raised when a remote method call failed.

negotiator_common.config

Configuration defaults for the negotiator project.

negotiator_common.config.BUILTIN_COMMANDS_DIRECTORY = '/home/docs/checkouts/readthedocs.org/user_builds/negotiator/checkouts/latest/common/negotiator_common/scripts'

The directory with built-in commands (a string).

negotiator_common.config.DEFAULT_TIMEOUT = 10

The number of seconds to wait for a reply from the other side (an integer).

If more time elapses an exception is raised causing the process to exit with a nonzero status code.

negotiator_common.config.GUEST_TO_HOST_CHANNEL_NAME = 'negotiator-guest-to-host.0'

The name of the channel that’s used for communication initiated by the guest (a string).

negotiator_common.config.HOST_TO_GUEST_CHANNEL_NAME = 'negotiator-host-to-guest.0'

The name of the channel that’s used for communication initiated by the host (a string).

negotiator_common.config.SUPPORTED_CHANNEL_NAMES = ('negotiator-guest-to-host.0', 'negotiator-host-to-guest.0')

A tuple of strings with supported channel names (containing GUEST_TO_HOST_CHANNEL_NAME and HOST_TO_GUEST_CHANNEL_NAME).

negotiator_common.config.USER_COMMANDS_DIRECTORY = '/usr/lib/negotiator/commands'

The pathname of the directory containing user defined commands that ‘the other side’ can invoke through negotiator.

negotiator_common.utils

Miscellaneous functionality.

class negotiator_common.utils.GracefulShutdown

Context manager to enable graceful handling of SIGTERM.

This context manager translates termination signals (SIGTERM) into TerminationError exceptions.

__enter__()

Start intercepting termination signals.

__exit__(exc_type, exc_value, traceback)

Stop intercepting termination signals.

signal_handler(signum, frame)

Raise TerminationError when the timeout elapses.

exception negotiator_common.utils.TerminationError

Exception that is raised when SIGTERM is received.

class negotiator_common.utils.TimeOut(num_seconds)

Context manager that enforces timeouts using UNIX alarm signals.

__enter__()

Schedule the timeout.

__exit__(exc_type, exc_value, traceback)

Clear the timeout and restore the previous signal handler.

__init__(num_seconds)

Initialize the context manager.

Parameters:num_seconds – The number of seconds after which to interrupt the running operation (an integer).
signal_handler(signum, frame)

Raise TimeOutError when the timeout elapses.

exception negotiator_common.utils.TimeOutError

Exception raised by the TimeOut context manager.

negotiator_common.utils.format_call(function, *args, **kw)

Format a Python function call into a human readable string.

Parameters:
  • function – The name of the function that’s called (a string).
  • args – The positional arguments to the function (if any).
  • kw – The keyword arguments to the function (if any).

Change log

The change log lists notable changes to the project:

Changelog

The purpose of this document is to list all of the notable changes to this project. The format was inspired by Keep a Changelog. This project adheres to semantic versioning.

Release 0.12.2 (2019-12-11)

Bug fix for 2 most recent releases: s/OSError/EnvironmentError/g

This is a follow up to / bug fix for release 0.12 and release 0.12.1 where I accidentally used OSError when I should have used IOError or the generic parent class EnvironmentError. I’ve verified that EnvironmentError is compatible with both Python 2.7 and 3.

The last few releases clearly show the value of having an automated test suite to guard against regressions, unfortunately due to the nature of the Negotiator project I’m not quite sure how I would get a functional test suite up and running on Travis CI.

It’s definitely possible, and on my wish list, but it is one of the higher hanging fruits on that -almost infinite- wish list, so don’t hold your breath 😛.

Release 0.12.1 (2019-12-09)

Enable retry in guest CLI.

This is a follow up to release 0.12 because I neglected to add retry=True to the negotiator_guest.cli module in that release (the new behavior is opt-in in the Python API so as to improve backwards compatibility and make the API more foolproof).

Release 0.12 (2019-12-05)

Retry character device access in guest agent when EBUSY error is reported.

At my employer we operate 200+ virtual servers that have Negotiator installed and in recent months we’ve started building more and more monitoring on top of Negotiator, resulting in hundreds of invocations per day. This is when I started seeing intermittent errors like the following:

IOError: [Errno 16] Device or resource busy: '/dev/vport2p2'

The new retry on EBUSY behavior is intended to minimize occurrences of such race conditions.

Release 0.11 (2019-10-11)

Fix error in error handling in negotiator-host

This resolves the traceback below when negotiator-host is running but ‘crashes’ because virsh list fails because it can’t connect to libvirtd. This situation is still an unrecoverable error, but the intention was for it to be an unrecoverable error that did not produce a traceback…

Traceback (most recent call last):
  File ".../negotiator_host/cli.py", line 117, in main
    action()
  File ".../negotiator_host/__init__.py", line 46, in __init__
    self.enter_main_loop()
  File ".../negotiator_host/__init__.py", line 53, in enter_main_loop
    self.update_workers()
  File ".../negotiator_host/__init__.py", line 62, in update_workers
    running_guests = set(find_running_guests())
  File ".../negotiator_host/__init__.py", line 270, in find_running_guests
    except ExternalCommandFailed:
NameError: global name 'ExternalCommandFailed' is not defined
Cleaned up flake8 F401 (imported but unused) warning
As a result of moving to humanfriendly.compact().
Minor changes relating to Python versions

Two minor changes relating to Python version compatibility:

  • Unbreak make docs (Sphinx insists on Python 3, and rightfully so).
  • Replace Python 2.6 reference in README with Python 2.7.

Compatibility with Python 3 hasn’t been verified but is more or less expected given a pure Python code base. Maybe a Unicode error slipped in here or there, as I said “to be verified”.

Release 0.10 (2019-03-03)

Clarify verbosity control
Update the command line interface usage messages to clarify that the options --verbose and --quiet can be repeated (in response to #1).
No traceback when guest discovery fails

Don’t log a traceback when guest discovery using the virsh list command fails, to avoid spamming the logs about a known problem. This change was made to counteract the following interaction:

  • The negotiator documentation specifically suggests to use a process supervision solution like supervisord to automatically restart the negotiator daemon when it dies.
  • When the libvirt daemon is down virsh list will fail and the negotiator daemon dies with a rather verbose traceback (before release 0.10).
  • Because supervisord automatically restarts the negotiator daemon but doesn’t know about the libvirt dependency, several restarts may be required to get the negotiator daemon up and running again.
  • This “restart until it stays up” interaction would result in quite a few useless tracebacks being logged which “polluted” the logs and might raise the impression that something is really broken (that can’t be fixed by an automatic restart).

Release 0.9 (2019-03-03)

Refactored channel discovery to use virsh list and virsh dumpxml:

  • The recent addition of Ubuntu 18.04 support proved once again that the old channel discovery strategy was error prone and hard to maintain.
  • Since then it had come to my attention that on Ubuntu 18.04 guest names embedded in pathnames of UNIX sockets may be truncated in which case the domain id provides the only way to match a UNIX socket to its guest.
  • Despite the previous point, I also wanted to maintain compatibility with libvirt releases that don’t embed the domain id in the pathnames. Doing so based on the old channel discovery strategy would have become messy.

So I decided to take a big step back and opted for a new strategy that will hopefully prove to be more robust and future proof. Thanks to @tarmack for initially suggesting this approach.

Release 0.8.6 (2019-02-25)

Follow-up to making channel discovery compatible with Ubuntu 18.04:

Release 0.8.5 (2019-02-23)

  • Made channel discovery compatible with Ubuntu 18.04 (related to #1).
  • Added this changelog, restructured the documentation.
  • Embedded CLI usage messages in readme and documentation.
  • Updated supervisord configuration examples to use stderr_logfile instead of redirect_stderr.
  • Other minor changes not touching the code base.

Release 0.8.4 (2016-04-08)

Follow-up to previous commit (Ubuntu 16.04 support).

Release 0.8.3 (2016-04-08)

Make channel discovery compatible with Ubuntu 16.04.

Release 0.8.2 (2015-10-29)

Make platform support more explicit in the documentation (Linux only, basically :-P).

Release 0.8.1 (2014-12-30)

Improve guest channel (re)spawning on hosts (improves robustness).

Release 0.8 (2014-11-01)

Proper sub process cleanup, more robust blocking read emulation.

Release 0.7 (2014-10-24)

Support for (custom) remote call timeouts with a default of 10s.

Release 0.6.1 (2014-09-28)

Bug fix for Python 2.6 compatibility (count() does not take keyword arguments).

Release 0.6 (2014-09-26)

  • Implemented blocking reads inside guests (don’t ask me how, please …).
  • Improved getting started instructions on adding virtual devices.
  • Rebranded s/generic/scriptable/g and improved the readme a bit.

Release 0.5.2 (2014-09-24)

Add syntax highlighting to the code and configuration samples in the readme and explicitly link to the online documentation available on Read the Docs.

Release 0.5.1 (2014-09-24)

  • Minor improvements and fixes to the documentation.
  • Properly documented the environment variables exposed to host commands.
  • Added trove classifiers to the setup.py scripts.
  • Bumped the version to release updated documentation to PyPI.

Release 0.5 (2014-09-24)

  • Support for proper bidirectional user defined command execution on both sides.
  • Improved the negotiator-guest usage message (by mentioning character device detection).

Release 0.2.1 (2014-09-22)

Fixed a typo in the readme, fixed a bug in the makefile and bumped the version so I could push a new release to PyPI because the readme was missing there (due to the makefile bug).

Release 0.2 (2014-09-22)

  • Added automatic character device selection.
  • Created online documentation on Read the Docs.

Release 0.1 (2014-09-22)

The initial commit and release.