Resolving DBus uniqe names

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Often you stumble across DBus logs (e.g. originating from bustle or dbus-monitor) which only feature DBus unique names (those :1.xyz numbers) and you can only guess which process it originates from.

Helper script to resolve those addresses to processes (if the system is still running):

#!/bin/bash
 
name=$1
while [ -n "$name" ]
do
    result=`LANG=C dbus-send \
                  --session \
                  --print-reply \
                  --dest=org.freedesktop.DBus \
                  / \
                  org.freedesktop.DBus.GetConnectionUnixProcessID \
                  string:"$name" 2>/dev/null`
    if [ $? -eq 0 ]
    then
        process=`ps ax | grep ^${result##* }`
        echo "$name -> $process"
    fi
    shift; name=$1
done

The QThread anti-pattern

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Sometimes with QThread you see something like this:

void run()
{
    while (true) {
        {
            QMutexLocker lock(&mMutexData);
            if (mQuit)
                break;
        }
 
        msleep (200);
    }
 
    mWaitExit.wakeAll();
}
 
void stop()
{
    mMutexData.lock();
    mQuit = true;
    mMutexData.unlock();
    mWaitExit.wait(&mMutexExit);
}

This is potentially problematic. Why? Consider the extreme case of a function shutdown() which does something like this:

void shutdown()
{
    thread->stop();
    delete thread;
}

Congratulations, you’ve just introduced a race condition. Why, you will ask? You’re waiting for the thread to end before deleting it, right?

No. And this has to do with the way Qt implements QThread::wait() which you should have probably used in the first place, if you really need this sort of functionality.

Qt hooks a pthread cleanup handler in the native thread which will call wakeAll() on a QWaitCondition stored inside the pimpl of QThread. And this pimpl – you might have guessed – is gone when you call delete.

Pino as in twitter

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Since Echofon cut off custom-built Firefoxes I was looking for a new twitter client. The only one matching my needs was Pino. Unfortunately since the mandatory activation of OAuth in twitter it stopped working. But: No fear! I hacked it to use librest which supports OAuth ootb. Currently it is a bit flaky (crashes at startup sometimes for no obvious reason) and there is no easy way to log in. It currently uses librest’s demo consumer keys which is probably not the most fortunate thing to do. I will request own credentials as soon as it runs more stable. Stay tuned for updates, I will push it to a public repository really soon.

Update: Seems upstream pino will contain librest with OAuth in version 0.3. So I’ll keep my ugly hack to myself ;-)

101 secret Rygel tips

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With the release of Rygel 0.7.3 I thought I should bring up some sort of FAQ for Rygel and especially the MediaExport plugin, since it has some features and behavior changes that might lead to confusion for long-time (and new) users:

Plugin concurrency

With the release of 0.7.4 you cannot enable both tracker and MediaExport plugins at once. If you do so, the MediaExport plugin will be shut down in favor of the tracker plugin.

Meta-data extraction

Speed

Since 0.7.3 Rygel now uses the gunp-dlna package for meta-data extraction. This is based on the gst-discoverer work by Arun and Edward from Collabora Multimedia. It is significantly faster on video files than the old home-grown meta-data extraction stuff.

Filters

Rygel no longer blindly tries to extract meta-data from everything it sees in the directories. Instead it uses a positive list of file extensions to include. In the default configuration these are:

  • Audio formats
    .mp3, .oga, .ogg, .mp4, .flac, .wav, .wma
  • Video formats
    .ogv, .ogg, .mkv, .avi, .mp4, .mpeg, .mpg, .ts. .wmv, .asf
  • Image formats
    .jpeg, .jpg

If your favorite format is missing, don’t hesitate to file a bug

Folder hierarchy

Since Rygel 0.5.2 there has been support for user-defined virtual folders in the MediaExport plugin. It allowed the user to browse through his media by artist and album e.g. With Rygel 0.7.3 the possibility to define those folders yourself is gone. The configuration syntax wasn’t really intuitive and easy to get wrong. We defined a set of build-in folders which resemble the folders provided by the Tracker plugin.

And since the addition of this default folders made the view of the root folder even more cluttered, I decided to move all every non-virtual folder that directly corresponds to a file-system folder into its own subfolder. In an upcoming release a configuration option to disable the display of this folder will be added.

If we missed out a folder you really need, please file a bug for it.

Screenshot of new hierarchy

State of the GUPnP stack on Windows and other scary tales

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I updated the windows ports of gssdp and gupnp today, did some further clean-up on the gupnp port and filed merge-requests for both on gitorious.

I also deleted the gupnp-win32 repository on github. New development will go to this repository on gitorious. There is still the gssdp-win32 repository on github since I have not yet taken care of the MSVC additions.

I also started wrapping gssdp et al into *mm (hey, I work for Openismus now ;) but this has proven to be somewhat difficult.

Trekstor Vibez and Jaunty^WLucid

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So – A year has passed, two Ubuntu versions, what’s the state of MTP vs. mass storage? Apparently still broken. Same same but different.

Instead of making the player crash, gphoto2/libmtp and usb mass storage fight for the right to access the device which leads to very ugly errors in dmesg that look like the device or at least its file-system is severely broken :(

So, once again: Either make the device MTP only or remove the device’s entry from the libmtp udev rules which now reside in /lib/udev/rules.d/45-libmtp8.rules

The X201, addendum

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The fingerprint reader

The fingerprint reader is a mess. It has the USB id (147e:2016) of the upeksonly driver in the fprint project, but it doesn’t work. The reader seems to work with the normal UPEK driver (either in thinkfinger or fprint) by modifying the supported USB id. But the answers it presents to the driver don’t seem to conform to anything it knows.

Kolmas viikola Helsingissä

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or: You’re holding it wrong. Seriously. Once upon a time, you could buy a IBM/Lenovo ThinkPad with Intel graphics and it just worked. While the Intel issues in the last versions of Ubuntu were mostly home-grown, the current disaster with the Core i3/i5 on-chip graphics isn’t. Like in the X201.

The Ubutu experience

Getting Ubuntu 10.4 LTS to work on an X201 isn’t too hard. You just need to follow some simple steps:

  1. Get Ubuntu (obviously) and put it on an USB stick; the X201 doesn’t have a CD drive
  2. Go to http://people.canonical.com/~hzhang/554569/ and grab the latest kernel package linked there (see also Launchpad bug 554569)
  3. Get the most recent BIOS update from Lenovo. A description on how to update your BIOS if you don’t have an optical drive may be found at thinkwiki.org
  4. Go to the BIOS setup and deactivate Intel AMT.
  5. Install Ubuntu normally. The installer should work just fine. If the graphical installer doesn’t, try the alternate install CD.
  6. After the installation is done, boot from USB once again and go into rescue mode to install the kernel package downloaded before.
  7. Boot normally.

Remaining issues

  • External video
    VGA works, but if you shut down the machine with the external monitor connected, it will somehow lockup (CPU is busy)
  • Suspend/Resume
    With the kernel from the launchpad bug, USB works after resume; the only thing I noticed is that sometimes the wireless LAN won’t come up again (like 1 in 10 resumes).
  • UltraBase
    No idea yet. Haven’t used though it is said that there are still problems with the display port on it