FOSDEM 2007

Here’s some notes about my visit to FOSDEM, in no particular order. I caught a cold (shouldn’t that be cold caught me?) and also managed to destroy my notes the week after so if I sound more incomprehensible than usual that’s probably because I am.

Pre-FOSDEM beer event. *burp*

Keynotes. I was somewhat distracted (planning the rest of the weekend, buying chocolates, hacking) during the keynotes so I mostly missed them. Liberating Java wasn’t as much about Java as it was about Sun’s vision related to working commercially as well as with communities. The evolution of software distribution models (bundled, shrink wrapped, services) had some interesting points. Showing that Sun has contributed significant amount of the code in Debian came as a surprise, hadn’t though about it, but felt a bit tacky marketing.

X.

AIGLX is about accelerated indirect GLX rendering, needed for OpenGL based compositing. And direct rendering is evil anyways. Even if we did have OpenGL on mobile devices I wonder if we have the memory to do compositing this way.

X security framework idea is to compartmentalize your X applications so that you can work on multiple projects (trusted / untrusted) on the same computer without risking information leaks. Quite important for NSA and the like. Funny limitations in old framework. New framework more flexible, but has similar problems to SELinux. How do you configure it so that it doesn’t get in the way? If it doesn’t get in the way how do you know it’s secure? The mental model is too complicated for the users. Using two laptops is much more simple, both in implementation and mental model.

Video on dope was quite crazy demonstration of using 3D hardware acceleration to do colorspace conversion and smooth out artefacts in videos. Curious way to use textures.

Everything new in X land was said to be blocking on new memory manager.

Debian. Automated testing of Debian packages, pbuilder, lintian, linda, piuparts. Interesting trivia: OpenOffice takes about 7.5h to build, using 40 nodes can build the whole Debian archive in the same time.

Formal dependency management (EDOS Project) had some interesting tools tracking package installability over time and is able to explain why certain package is not installable (anymore.) This might be interesting for Sardine.

Development platforms.
gtk+ upstream meeting. I have a feeling the desktop distributions are content with gtk+ and are not investing in pushing it forwards, or even maintaining it much. The mobile players on the other hand are only getting started ;-) ABI break is an acute problem for maemo gtk due to our modifications (no free expansion slots left.) We need to fiture out where we want to go and whether API/ABI break can help us getting there. For example, gtk+ uses cairo/Xlib, but when you have OpenGL hardware you could use from the widgets (there’s experimental cairo/glitz backend) how do you mix the two?

Bling it up. Mmm, eye candy. You can do lots of nice effects with cairo. Now, how do we make it trivial to integrate those effects into applications?

OpenMockupOpenMoko (Sorry, couldn’t resist. I blame MDK for coming up with the term.) Starting to feel the performance, the processor is even slower than ours, no FPU of course. The pixbuf engine with its bilinear (floating points based) scaling is really hurting. Switching to sapwood should give noticeable performance increase with some tradeoffs.

The display on the device is even higher density (280ppi) than ours (250ppi) The text is physically smaller but still readable, at least for me. The widgets are rather small, especially the ones around screen edges are almost impossible to use without stylus. I couldn’t find a stylus holder on the casing – whoopsie.

Talking to Mickey made me think their approach to developing applications is appealing. Single implementation for the basic navigation saves a lot of effort while enforcing familiar behavior in places where differentiation doesn’t buy you much.

Qtopia. Spying around a bit. I think there’s quite a bit we could learn from them about producing development platforms.

Web 2.0 in just under 5 minutes

When in doubt, iterate faster


This leads to Boyd’s Law of Iteration: speed of iteration beats quality of iteration.

[…]

When in doubt, iterate faster.

Besides an interesting reference to dogfights between jet fighters, specifically between MiG-15s and F-86s, one quote caught my attention:

An enterprise architecture is a description of the goals of an organization, how these goals are realized by business processes, and how these business processes can be better served through technology.

A Better Path to Enterprise Architectures

The first thing that comes to mind from enterprise architectures is EJB
which in my mind has no connection to the quote above.

But maybe that’s just me mixing one Enterprise with another.

DIY 770 robot

Some crazy 770 hackers present: The Puppy Robot. Coming soon to toystores near you(?) :-)

Things I didn’t know about the waterfall model

The most cited paper “describing” the waterfall model argues against using it. Way to go with the sources. Oh the pain misreading an article has caused to software development. (Craig Larman visited us and gave an introduction to Agile methods today.)

Cool code generation

Just when we were leaving DAM3 Jim Gettys mentioned some fancy code generating technology. Apparently it can be used, among other things, to write a javascript VM that is an order of magnitude faster than current ones. He also mentioned having just finished a meeting (with Carl Worth, Alan Kay and others) where they implemented the core parts of cairo using this new thingamagic and got it correct in a few hours. It is conceivable that this thing could be used for selected parts of cairo and render extension and get big performance benefits. Can’t wait to hear more about this.

Notes from the DAM

Here’s some random notes from the Desktop Architects Meeting-3. Follow the link for summary and presentations.

The format was somewhat different from what I was expecting; I think we spent too much time (too many and too long) on the presentations, at the expense of breakout sessions. Breakouts themselves were great, but in some cases the problems can not be solved with technology (codecs, DRM) or we did not have the right people present to get a concrete action plan (upstream/downstream co-operation.) All in all, it was good, could’ve been better.

The DAM is a good place to meet the people working on different aspects of the Linux desktop and have a glance to the big picture on what’s happening in different areas. Following are some things we discussed during the two days.

ISVs want one stable platform. Never ever remove or change anything, adding is OK. ISVs do not want to keep on porting the software. Once an applications is released it should run (everywhere.) You can rebuild the distribution to migrate from libstdc++.so.5 to libstdc++.so.6 and drop the former without affecting the distribution, but that easily breaks independent applications. Having compatibility libraries is nice in theory, but in practice there is no distribution independent way for getting them installed.

If ISVs agree on some common set of libraries and APIs they’d all be happy about, there might be enough incentive for distributions to keep making that set of libraries available. Have them all installed by default, or get distributions provide a single well known way to get them installed on end user systems.

At least in theory we currently have two totally incompatible Nokia 770’s out there. Some (really few I’d expect) with the 2005 and the rest with the 2006 OS release. This presents a problem to ISVs, what does “runs on Nokia 770″ really mean? And when/if we release new hardware/software combinations, how can we get the message clear to both ISVs and end users about platform compatibility?

Audio on Linux is in a sorry state. On Windows there’s one audio API, on Mac there’s one API, on Linux there’s 6-7 incompatible APIs. It’s relatively futile to talk about video if even audio doesn’t work. And with codecs/DRM the problems are not really technical anyway. Focusing on the needs of application developers is the way to go here.

In Maemo we’re using GStreamer and ESD basically for the same reason, there is no one API that would work for all, or even the most common, cases.

Improving upstream/downstream co-operation.
Currently the technology (read: bugzilla) does not help as much here as it could, there’s much manual work involved; forwarding bugs to upstream, searching through all (other) distribution bugzillas for bugfixes, etc. It would be nice to have an overview of the state of a bug across all distributions. Does any distribution have a proposed fix? Is the bug officially fixed upstream? Where can one find a patch to backport to maintenance release? And so on.

Unfortunately we could only collect use cases as we didn’t have the right people present to concretely plan for getting things done.

Qt applications should look native. Qt4 adds lots of support to make this possible (cleanlooks theme, integrating with glib mainloop, button order.) In Maemo integrating with the input methods is the only thing I can think of that might be tricky to do. Theming and other overall look and feel is simply straightforward work that just needs to be done methinks.

D-Bus 1.0 guarantees API/ABI stability. No more need for “I know this is unstable” defines. No more worries about changing APIs.

DAM if you do, DAM if you don’t

Arrived in Portland this morning (Portland time, my local time was 9pm or so) as I’ll be attending the desktop architects meeting next two days. Ought to be interesting.

The X bug that wasn’t

Turns out the X bug (about motion events) was in fact bug #380281 in gtk. Basically gtk widgets just won’t work correctly if you use gtk_widget_set_extension_events() on them. Arguably that could be considered acceptable for stock widgets and gtk_widget_set_extension_events() intended only for custom widgets.

Unfortunately we need extension events to work on stock widgets so that we can do different things on thumb press and stylus press. I’ve fixed most relevant issues to our gtk+ but it would be nice to have things fixed upstream. Maintaining a fork is not so much fun.

Adventures in the kdrive land

Got this bug which lead me into looking at some code in the X server. If you use gtk_widget_set_extension_events(w, GDK_EXTENSION_EVENTS_ALL); on a GtkEntry or GtkTextView motion notify events stop working. This effectively prevents selecting text.

Button press is always generated at 0,0 (root window coordinates) and the next motion notify is at the “right” position so it looks like a really quick drag and I think here gtk is getting confused. After that you get one more motion notify and then everything stops. Dragging the pointer outside the widget and back in again emits exactly one motion notify event for each time the pointer enters the widget again.

Who’s eating the motion notify events? Ideas?

Anyway.. When I first started replicating the problem I fired up the test program in Xephyr and *BOOM* Xephyr crashed. Long story short I ended up looking at the following pieces of code:

--- fb/fbpict.c:
void fbCompositeSolidMask_nx8x8888 (FbComposeData *params)

--- fb/fbmmx.c:
void fbCompositeSolidMask_nx8x8888mmx (CARD8      op,
                                       PicturePtr pSrc,
                                       PicturePtr pMask,
                                       PicturePtr pDst,
                                       INT16      xSrc,
                                       INT16      ySrc,
                                       INT16      xMask,
                                       INT16      yMask,
                                       INT16      xDst,
                                       INT16      yDst,
                                       CARD16     width,
                                       CARD16     height)

--- fb/fbpict.c:
if (fbHaveMMX())
    func = fbCompositeSolidMask_nx8x8888mmx;
else
    func = fbCompositeSolidMask_nx8x8888;

[and then later on]
(*func) (&params);

I have a pretty good idea what/who happened but to protect the guilty let’s not name any names.

Disabling MMX there let me move on to figure out the actual problem. After fixing a potential issue in gtk (no help there) I found myself staring at more X server code:

--- hw/kdrive/src/kinput.c:
if (some test) {
    [nested if doing conditional coordinate transformation]
}
else {
    [exactly the same code as in previous branch]
}

…and…

--- include/inputstr.h:
#define POINTER_RELATIVE (1

I've no idea whether that's related, but if the bug is in X server (the same testcase works with desktop X) and the rest of the code is equally (un)obvious it's going to be fun to track down.