Development

The first step is to install labgrid into a local virtualenv.

Installation

Clone the git repository:

git clone https://github.com/labgrid-project/labgrid && cd labgrid

Create and activate a virtualenv for labgrid:

virtualenv -p python3 venv
source venv/bin/activate

Install required dependencies:

sudo apt install libow-dev

Install the development requirements:

pip install -r dev-requirements.txt

Install labgrid into the virtualenv in editable mode:

pip install -e .

Tests can now be run via:

python -m pytest --lg-env <config>

Writing a Driver

To develop a new driver for labgrid, you need to decide which protocol to implement, or implement your own protocol. If you are unsure about a new protocol’s API, just use the driver directly from the client code, as deciding on a good API will be much easier when another similar driver is added.

Labgrid uses the attrs library for internal classes. First of all import attr, the protocol and the common driver class into your new driver file.

import attr

from labgrid.driver.common import Driver
from labgrid.protocol import ConsoleProtocol

Next, define your new class and list the protocols as subclasses of the new driver class. Try to avoid subclassing existing other drivers, as this limits the flexibility provided by connecting drivers and resources on a given target at runtime.

import attr

from labgrid.driver.common import Driver
from labgrid.protocol import ConsoleProtocol

@attr.s(cmp=False)
class ExampleDriver(Driver, ConsoleProtocol):
    pass

The ConsoleExpectMixin is a mixin class to add expect functionality to any class supporting the ConsoleProtocol and has to be the first item in the subclass list. Using the mixin class allows sharing common code, which would otherwise need to be added into multiple drivers.

import attr

from labgrid.driver.common import Driver
from labgrid.driver.consoleexpectmixin import ConsoleExpectMixin
from labgrid.protocol import ConsoleProtocol

@attr.s(cmp=False)
class ExampleDriver(ConsoleExpectMixin, Driver, ConsoleProtocol)
    pass

Additionally the driver needs to be registered with the target_factory and provide a bindings dictionary, so that the Target can resolve dependencies on other drivers or resources.

import attr

from labgrid.factory import target_factory
from labgrid.driver.common import Driver
from labgrid.driver.consoleexpectmixin import ConsoleExpectMixin
from labgrid.protocol import ConsoleProtocol

@target_factory.reg_driver
@attr.s(cmp=False)
class ExampleDriver(ConsoleExpectMixin, Driver, ConsoleProtocol)
    bindings = { "port": SerialPort }
    pass

The listed resource SerialPort will be bound to self.port, making it usable in the class. Checks are performed that the target which the driver binds to has a SerialPort, otherwise an error will be raised.

If your driver can support alternative resources, you can use a set of classes instead of a single class:

bindings = { "port": {SerialPort, NetworkSerialPort}}

Optional bindings can be declared by including None in the set:

bindings = { "port": {SerialPort, NetworkSerialPort, None}}

If you need to do something during instantiation, you need to add a __attr_post_init__ method (instead of the usual __init__ used for non-attr-classes). The minimum requirement is a call to super().__attr_post_init__().

import attr

from labgrid.factory import target_factory
from labgrid.driver.common import Driver
from labgrid.driver.consoleexpectmixin import ConsoleExpectMixin
from labgrid.protocol import ConsoleProtocol

@target_factory.reg_driver
@attr.s(cmp=False)
class ExampleDriver(ConsoleExpectMixin, Driver, ConsoleProtocol)
    bindings = { "port": SerialPort }

    def __attr_post_init__(self):
        super().__attr_post_init__()

All that’s left now is to implement the functionality described by the used protocol, by using the API of the bound drivers and resources.

Writing a Resource

To add a new resource to labgrid, we import attr into our new resource file. Additionally we need the target_factory and the common Resource class.

import attr

from labgrid.factory import target_factory
from labgrid.driver.common import Resource

Next we add our own resource with the Resource parent class and register it with the target_factory.

import attr

from labgrid.factory import target_factory
from labgrid.driver.common import Resource


@target_factory.reg_resource
@attr.s(cmp=False)
class ExampleResource(Resource):
    pass

All that is left now is to add attributes via attr.ib() member variables.

import attr

from labgrid.factory import target_factory
from labgrid.driver.common import Resource


@target_factory.reg_resource
@attr.s(cmp=False)
class ExampleResource(Resource):
    examplevar1 = attr.ib()
    examplevar2 = attr.ib()

The attr.ib() style of member definition also supports defaults and validators, see the attrs documentation.

Writing a Strategy

Labgrid only offers two basic strategies, for complex use cases a customized strategy is required. Start by creating a strategy skeleton:

import enum

import attr

from labgrid.step import step
from labgrid.driver.common import Strategy

class Status(enum.Enum):
    unknown = 0

class MyStrategy(Strategy):
    bindings = {
    }

    status = attr.ib(default=Status.unknown)

    @step
    def transition(self, status, *, step):
        if not isinstance(status, Status):
            status = Status[status]
        if status == Status.unknown:
            raise StrategyError("can not transition to {}".format(status))
        elif status == self.status:
            step.skip("nothing to do")
            return  # nothing to do
        else:
            raise StrategyError(
                "no transition found from {} to {}".
                format(self.status, status)
            )
        self.status = status

The bindings variable needs to declare the drivers necessary for the strategy, usually one for power, boot loader and shell. The Status class needs to be extended to cover the states of your strategy, then for each state an elif entry in the transition function needs to be added.

Lets take a look at the builtin BareboxStrategy. The Status enum for Barebox:

class Status(enum.Enum):
    unknown = 0
    barebox = 1
    shell = 2

defines 2 custom states and the unknown state as the start point. These two states are handled in the transition function:

elif status == Status.barebox:
    # cycle power
    self.target.activate(self.power)
    self.power.cycle()
    # interrupt barebox
    self.target.activate(self.barebox)
elif status == Status.shell:
    # tansition to barebox
    self.transition(Status.barebox)
    self.barebox.boot("")
    self.barebox.await_boot()
    self.target.activate(self.shell)

Here the barebox state simply cycles the board and activates the driver, while the shell state uses the barebox state to cycle the board and than boot the linux kernel.

Contributing

Thank you for thinking about contributing to labgrid! Some different backgrounds and use-cases are essential for making labgrid work well for all users.

The following should help you with submitting your changes, but don’t let these guidelines keep you from opening a pull request. If in doubt, we’d prefer to see the code earlier as a work-in-progress PR and help you with the submission process.

Workflow

  • Changes should be submitted via a GitHub pull request.
  • Try to limit each commit to a single conceptual change.
  • Add a signed-of-by line to your commits according to the Developer’s Certificate of Origin (see below).
  • Check that the tests still work before submitting the pull request. Also check the CI’s feedback on the pull request after submission.
  • When adding new drivers or resources, please also add the corresponding documentation and test code.
  • If your change affects backward compatibility, describe the necessary changes in the commit message and update the examples where needed.

Code

  • Follow the PEP 8 style.
  • Use attr.ib attributes for public attributes of your drivers and resources.
  • Use isort to sort the import statements.

Documentation

Developer’s Certificate of Origin

Labgrid uses the Developer’s Certificate of Origin 1.1 with the same process as used for the Linux kernel:

Developer’s Certificate of Origin 1.1

By making a contribution to this project, I certify that:

  1. The contribution was created in whole or in part by me and I have the right to submit it under the open source license indicated in the file; or
  2. The contribution is based upon previous work that, to the best of my knowledge, is covered under an appropriate open source license and I have the right under that license to submit that work with modifications, whether created in whole or in part by me, under the same open source license (unless I am permitted to submit under a different license), as indicated in the file; or
  3. The contribution was provided directly to me by some other person who certified (a), (b) or (c) and I have not modified it.
  4. I understand and agree that this project and the contribution are public and that a record of the contribution (including all personal information I submit with it, including my sign-off) is maintained indefinitely and may be redistributed consistent with this project or the open source license(s) involved.

Then you just add a line (using git commit -s) saying:

Signed-off-by: Random J Developer <random@developer.example.org>

using your real name (sorry, no pseudonyms or anonymous contributions).

Ideas

Driver Priorities

In more complex use-cases, we often have multiple drivers implementing the same Protocols on the same Target. For example:

CommandProtocol (ShellDriver and SSHDriver):
The SSHDriver may not be active all the time, but should be preferred when it is.
ResetProtocol (DigitalOutputResetDriver and NetworkPowerPort via power cycling):
This will occour when we implement the ResetProtocol as below. The real reset driver should be preferred in that case.

To avoid a central precedence list (which would be problematic for third-party drivers), each driver should declare its precedence per protocol relative other drivers by referencing them by class name. This way, the Target can sort them at runtime.

Driver Preemption

To allow better handling of unexpected reboots or crashes, inactive Drivers could register callbacks on their providers (for example the BareboxDriver it’s ConsoleProtocol). These callbacks would look for indications that the Target has changed state unexpectedly (by looking for the bootloader startup messages, in this case). The inactive Driver could then cause a preemption and would be activated. The current caller of the originally active driver would be notified via an exception.

File Transfer to Exporters

Currently, the exporter and client expect to have a shared filesystem (see for example how the AndroidFastbootDriver works when accessing a NetworkAndroidFastboot resource). To remove this limitation, we should have a common way to make files available to the exporter, possibly by generating a hash locally and rsyncing new files to the exporter.

Remote Target Reservation

For integration with CI systems (like Jenkins), it would help if the CI job could reserve and wait for a specific target. This could be done by managing a list of waiting users in the coordinator and notifying the current user on each invocation of labgrid-client that another user is waiting. The reservation should expire after some time if it is not used to lock the target after it becomes available.

ResetProtocol

Resetting a board is a distinct operation from cycling the power and is often triggered by pushing a button (automated via a relays or FET). If a real reset is unavailable, power cycling could be used to emulate the reset. Currently, the DigitalOutputPowerDriver implements the PowerProtocol instead, mixing the two aspects.

To handle falling back to emulation via the PowerProtocol nicely, we would need to implement Driver Priorities

Step Tracing

The Step infrastructure already collects timing and nesting information on executed commands, but is currently only used for in pytest or via the standalone StepReporter. By writing these events to a file (or sqlite database) as a trace, we can collect data over multiple runs for later analysis. This would become more useful by passing recognized events (stack traces, crashes, ...) and benchmark results via the Step infrastructure.

Target Feature Flags

It would be useful to support configuring feature flags in the target YAML definition. Then individual tests could be skipped if a required feature is unavailable on the current target without manually modifying the test suite.