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  1. 5381e39 Replace `unstable` with `staging` by Jonas Ådahl · 9 days ago master
  2. b1670b4 xdg-foreign: add error enums by Simon Ser · 9 days ago
  3. 17bef0e pointer-gestures: correct description of pinch by Peter Hutterer · 10 days ago
  4. af29ece fullscreen-shell: Clarify that present requests assign a surface role by Vlad Zahorodnii · 3 weeks ago
  5. 3683a5e linux-dmabuf: clarify what mixed valid/INVALID modifiers mean by Simon Ser · 3 weeks ago

Wayland protocols

wayland-protocols contains Wayland protocols that add functionality not available in the Wayland core protocol. Such protocols either add completely new functionality, or extend the functionality of some other protocol either in Wayland core, or some other protocol in wayland-protocols.

A protocol in wayland-protocols consists of a directory containing a set of XML files containing the protocol specification, and a README file containing detailed state and a list of maintainers.

Protocol phases

Protocols in general has three phases: the development phase, the testing phase, and the stable phase.

In the development phase, a protocol is not officially part of wayland-protocols, but is actively being developed, for example by iterating over it in a merge request, or planning it in an issue.

During this phase, patches for clients and compositors are written as a test vehicle. Such patches must not be merged in clients and compositors, because the protocol can still change.

When a protocol has reached a stage where it is ready for wider adoption, and after the GOVERNANCE section 2.3 requirements have been met, it enters the “testing” phase. At this point, the protocol is added to staging/ directory of wayland-protocols and made part of a release. What this means is that implementation is encouraged in clients and compositors where the functionality it specifies is wanted.

Extensions in staging cannot have backward incompatible changes, in that sense they are equal to stable extensions. However, they may be completely replaced with a new major version, or a different protocol extension all together, if design flaws are found in the testing phase.

After a staging protocol has been sufficiently tested in the wild and proven adequate, its maintainers and the community at large may declare it “stable”, meaning it is unexpected to become superseded by a new major version.

Deprecation

A protocol may be deprecated, if it has been replaced by some other protocol, or declared undesirable for some other reason. No more changes will be made to a deprecated protocol.

Legacy protocol phases

An “unstable” protocol refers to a protocol categorization policy previously used by wayland-protocols, where protocols initially placed in the unstable/ directory had certain naming conventions were applied, requiring a backward incompatible change to be declared “stable”.

During this phase, protocol extension interface names were in addition to the major version postfix also prefixed with z to distinguish from stable protocols.

Protocol directory tree structure

Depending on which stage a protocol is in, the protocol is placed within the toplevel directory containing the protocols with the same stage. Stable protocols are placed in the stable/ directory, staging protocols are placed in the staging/ directory, and deprecated protocols are placed in the deprecated/ directory.

Unstable protocols (see Legacy protocol phases) can be found in the unstable/ directory, but new ones should never be placed here.

Protocol development procedure

To propose a new protocol, create a GitLab merge request adding the relevant files and Makefile.am entry to the repository with the explanation and motivation in the commit message. Protocols are organized in namespaces describing their scope (“wp”, “xdg” and “ext”). There are different requirements for each namespace, see GOVERNANCE section 2 for more information.

If the new protocol is just an idea, open an issue on the GitLab issue tracker. If the protocol isn't ready for complete review yet and is an RFC, create a merge request and add the “WIP:” prefix in the title.

To propose changes to existing protocols, create a GitLab merge request.

Interface naming convention

All protocols should avoid using generic namespaces or no namespaces in the protocol interface names in order to minimize risk that the generated C API collides with other C API. Interface names that may collide with interface names from other protocols should also be avoided.

For generic protocols not limited to certain configurations (such as specific desktop environment or operating system) the wp_ prefix should be used on all interfaces in the protocol.

For protocols allowing clients to configure how their windows are managed, the xdg_ prefix should be used.

For operating system specific protocols, the interfaces should be prefixed with both wp_ and the operating system, for example wp_linux_, or wp_freebsd_, etc.

For more information about namespaces, see GOVERNANCE section 2.1 .

Each new protocol XML file must include a major version postfix, starting with -v1. The purpose of this postfix is to make it possible to distinguish between backward incompatible major versions of the same protocol.

The interfaces in the protocol XML file should as well have the same major version postfix in their names.

For example, the protocol foo-bar may have a XML file foo-bar/foo-bar-v1.xml, consisting of the interface wp_foo_bar_v1, corresponding to the major version 1, as well as the newer version foo-bar/foo-bar-v2.xml consisting of the interface wp_foo_bar_v2, corresponding to the major version 2.

Include a disclaimer

Include the following disclaimer:

Warning! The protocol described in this file is currently in the testing
phase. Backward compatible changes may be added together with the
corresponding interface version bump. Backward incompatible changes can
only be done by creating a new major version of the extension.

Backward compatible protocol changes

A protocol may receive backward compatible additions and changes. This is to be done in the general Wayland way, using version and since XML element attributes.

Backward incompatible protocol changes

While not preferred, a protocol may at any stage, especially during the testing phase, when it is located in the staging/ directory, see backward incompatible changes.

Assuming a backward incompatible change is needed, the procedure for how to do so is the following:

  • Make a copy of the XML file with the major version increased by 1.
  • Increase the major version number in the protocol XML by 1.
  • Increase the major version number in all of the interfaces in the XML by 1.
  • Reset the interface version number (interface version attribute) of all the interfaces to 1.
  • Remove all of the since attributes.

Declaring a protocol stable

Once it has been concluded that a protocol been proven adequate in production, and that it is deemed unlikely to receive any backward incompatible changes, it may be declared stable.

The procedure of doing this is the following:

  • Create a new directory in the stable/ toplevel directory with the same name as the protocol directory in the staging/ directory.
  • Copy the final version of the XML that is the version that was decided to be declared stable into the new directory. The target name should be the same name as the protocol directory but with the .xml suffix.
  • Remove the disclaimer about the protocol being in the testing phase.
  • Update the README file in the staging directory and create a new README file in the new directory.
  • Replace the disclaimer in the protocol files left in the staging/ directory with the following:
Disclaimer: This protocol extension has been marked stable. This copy is
no longer used and only retained for backwards compatibility. The
canonical version can be found in the stable/ directory.

Note that the major version of the stable protocol extension, as well as all the interface versions and names, must remain unchanged.

There are other requirements for declaring a protocol stable, see GOVERNANCE section 2.3.

Releases

Each release of wayland-protocols finalizes the version of the protocols to their state they had at that time.

Gitlab conventions

Triaging merge requests

New merge requests should be triaged. Doing so requires the one doing the triage to add a set of initial labels:

~“New Protocol” - For a new protocol being added. If it's an amendment to an existing protocol, apply the label of the corresponding protocol instead. If none exist, create it.

~“Needs acks” - If the protocol needs one or more acknowledgements.

~“Needs implementations” - If there are not enough implementations of the protocol.

~“Needs review” - If the protocol is in need of review.

~“In 30 day discussion period” - If the protocol needs a 30 day discussion period.

For the meaning and requirement of acknowledgments and available implementations, see the GOVERNANCE.md document.

Managing merge requests

When merge requests get their needed feedback and items, remove the corresponding label that marks it as needing something. For example, if a merge request receives all the required acknowledgments, remove the ~“Needs acks” label, or if 30 days passed since opening, remove any ~“In 30 days discussion period” label.

Nacking a merge request

If the inclusion of a merge request is denied due to one or more Nacks, add the ~Nacked label.