X.Org releases: present and future

The X.Org Foundation released xorg-server 1.7 on October 1st, in preparation for the imminent release of X11R7.5. Users can look forward to improvements in display configuration, screen transformation, and input devices, including the much-anticipated Multi-Pointer X (MPX) code that supports multiple independent keyboard focus points and mouse pointers. At the same time, the development team is drawing up plans to adopt a new release process to accommodate a predictable release schedule and better testing.

What's new with 1.7 and 7.5

Lower-level changes in the new release include several new display-oriented technologies: support for Extended Extended display identification data (E-EDID) and an update to the X Resize, Rotate and Reflect Extension (XRandR). Another proposed update, the "Shatter" enhancement to the EXA acceleration architecture, was deferred to a future release.

E-EDID is a revision of the EDID format with which monitors provide a machine-readable list of capabilities to attached graphics cards. E-EDID supports longer strings than EDID, localization of strings, and adds fields for aspect ratio changing and additional timing and frequency formulas. E-EDID will eventually be superseded by a newer format called DisplayID, but is of particular importance to home electronics users because of its usage in HDMI devices.

XRandR 1.3 adds two new capabilities: projective transforms and panning. Projective Transforms allow more generalized transformations of the image buffer than the previously supported rotation and reflection. This will allow transforms to correct for keystoning and other distortion, as well as scaling of the image buffer. If the displayed desktop is smaller than the virtual screen size, enabling Panning will allow the display to follow the cursor automatically.

The deferred project Shatter was one of X.Org's Google Summer of Code projects, and when integrated will allow screens to be split between multiple framebuffers.

Input devices also see changes in this release, most notably with MPX. As the name indicates, MPX allows multiple input devices to be used at once. That does not mean merely the ability to plug in two mice and two keyboards physically; X has supported that for a long time. But without MPX, multiple attached mice both control the same pointer, and multiple keyboards both route keystrokes into the same input stream. MPX allows for multiple, separate cursors, with separate focus behavior. Some X applications and toolkits will require modification to work with MPX, as they hard-code in the assumption that there is only one keyboard and pointer.

MPX is part of a larger revision to the X input system named XInput2. XInput2 builds on the previous XInput API, and adds other features such as Input Device Properties, a mechanism through which generic properties can be attached to input devices to report special characteristics to the X server and client applications. Such properties might include mouse button timeouts, pointer acceleration, or even logical names (such as distinguishing between multiple attached mice).

Other updates to specific subsystems include changes for Mesa, SELinux, and VGA arbitration, enhancements to the XQuartz server designed for Mac OS X, as well as the deprecation of several obsolete and unmaintained modules and extensions.

The process for 1.8

Peter Hutterer proposed reworking the X.Org release process in an email to the xorg-devel mailing list on September 26. He cited three problems with the existing process: an unpredictable schedule, too much development in the git master that frequently leaves it broken and unusable, and a too-short testing cycle that occurs late in the release process. He noted that the three problems were tightly related, and proposed that the project adopt a timed, predictable release schedule with separate windows for feature merging, bug fixing, and final testing.

The proposed process begins with starting separate branches for new features, rather than developing them as patch sets that could disrupt master. For each release cycle, the project would then use a three month merge window to integrate the feature branches into master, then enter into a two-month bug fix window, and finally freeze master for a one-month release window, during which time a release manager is in charge, and only crucial fixes are merged in. The result, argued Hutterer, would be a predictable six-month release cycle, and a much easier environment for testers.

Keith Packard questioned whether 3:2:1 was the best ratio for feature merging, bug fixing, and release freezing, specifically noting that the feature merge window was considerably larger than that used by the Linux kernel team. Hutterer replied that he thought it was a good starting value, particularly due to the fact that the entire process was new, but added that he thought every facet of the process should be reviewed after the 1.8 cycle, including possibly shortening the merge window.

The effect on testing was particularly popular with the other developers on the list during the subsequent discussion. Several contrasted X.Org's differences from the Linux kernel, beginning with the relative scarcity of X.Org testers. The consensus in the thread was that the history of an unstable git master and lack of documentation to guide willing testers in building and testing the code was to blame; a revised release process with a stable master and individual feature branches could go a long way towards building a community of active X.Org testers.

Hutterer made his proposal on the list because he was unable to attend the 2009 X Developers' Conference (XDC), held in Portland September 28-30. The XDC attendees discussed the proposal, after which Daniel Stone posted their decisions to xorg-devel. The group plans to adopt the basic proposed model for the xorg-server 1.8 / X11R7.6 release cycle, with the addition of choosing release managers for each cycle and asking developers to adopt per-subsystem trees in same manner that the Linux kernel developers use for subsystem maintenance.

Stone's email generated its own controversy thanks to its suggestion that if the the new process is a success for the 1.8/7.6 cycle, then the next step would be to merge graphics drivers into the main xorg-server tree for the 1.10/7.7 cycle. The arguments against merging drivers into the main xorg-server code base included license incompatibilities, but ultimately more developers deemed the simplicity of maintaining drivers in the same codebase as the server to be a long-term win. Still, that change in source code management is still just a proposal, and one slated for two release cycles in the future.

Ultimately, the goal of the proposed new release process is to make the main X.Org codebase more stable, more predictable, and as a result, easier to test. As several on the xorg-devel list pointed out, xorg-server is used on just as many systems as the Linux kernel, but has only a fraction of the active testers that help make the kernel so robust. X.Org continues to make improvements and enhancements with every release, and long gone are the naysayers of a decade ago who proposed ditching X altogether. Hopefully, X11R7.6 and xorg-server 1.8 will arrive on schedule six months from now, and will show the fruits of a longer and more determined testing process, too.