Wednesday, October 04, 2017

External Source kernel modules install does not fail as it should

Another small post to serve for future memory that when you are building Linux Kernel modules from external tree source, the kernel build system behaves differently. Yesterday it happened that I lost a huge amount of time trying to understand why the installation of a module was not exiting with error, when I clearly saw errors in the logs. The reason is that this is on purpose. In the build scripts for kernel installation there is this hidden gem: Don't stop modules_install if we can't sign external modules. I have been warned.

Monday, August 28, 2017

ParseError not a BitBake file

This error occurred to me when I made a require or include with the path to the file inside " quotation marks. The error message of course just said that  

ERROR: ParseError in "conf/machine/include/": not a BitBake file

Solution: Remove the quotation marks around the file path in any require or include directives.

Tuesday, July 18, 2017

A script that pause/plays on lock/unlock Spotify

A script that pause/plays on lock/unlock

dbus-monitor --session "type='signal',interface='org.gnome.ScreenSaver',member='ActiveChanged'" | \
  while true; do
    read X
    echo $X
    if echo $X | grep "boolean true" &> /dev/null; then
        dbus-send --print-reply --dest=org.mpris.MediaPlayer2.spotify /org/mpris/MediaPlayer2 org.mpris.MediaPlayer2.Player.PlayPause
    elif echo $X | grep "boolean false" &> /dev/null; then
        dbus-send --print-reply --dest=org.mpris.MediaPlayer2.spotify /org/mpris/MediaPlayer2 org.mpris.MediaPlayer2.Player.PlayPause

Sunday, May 07, 2017

readlink system call fails on other files besides symbolic links

I just write this post to remind myself that the readlink system call fails on non symbolic links. I was expecting that it would work on files and directories but it doesn't.

man 2 readlink says in one of the errno:

EINVAL The named file is not a symbolic link.

So the next step is to check if the path is a symbolic link or not. The first choice would be to use stat on the path, but stat will give you results from the dereferenced file, not the symbolic link. So using stat system call on a file will never tell you if the file is a symbolic link.

lstat()  is  identical  to  stat(), except that if pathname is a symbolic link, then it returns
       information about the link itself, not the file that it refers to.

There you have it for future reference:

std::string MountHandler::doReadlink(std::string const& path) {
    char buff[PATH_MAX];
    struct stat stat_buf = {};
    if (lstat(path.c_str(), &stat_buf) == -1)
        throw std::runtime_error(fmtString("Could not stat path %s. Errno: %s",
        path.c_str(), strerror(errno)));

    if (!S_ISLNK(stat_buf.st_mode))
        return path;

    ssize_t len = readlink(path.c_str(), buff, sizeof (buff) - 1);
    if (len == -1) {
        throw std::runtime_error(fmtString("Readlink failed on %s. errno %s",
            path.c_str(), strerror(errno)));
    buff[len] = '\0';
    return std::string(buff);

Sunday, April 16, 2017

Breaking abstract class interface in C++

Today while working on some code I had the need to make a tiny-bit-small break on a contract from an abstract base class.

The case is that I had an abstract base class called Pin, that contracted 2 methods for subclasses. The problem is that the InputPin class while benefiting from other functionality provided by the class Pin, could not sensibly provide a setPinValue method. Imagine I am naive and will only inform this operation is impossible on runtime:

volatile bool pinA1 = false;

class Pin {
 virtual void setPinValue(bool value) = 0;
 virtual bool getPinValue() const = 0;
 virtual ~Pin() {}

class InputPin : public Pin {
 virtual void setPinValue(bool value) { throw std::runtime_error("Cannot set value on input pin"); }
 virtual bool getPinValue() const { return pinA1 };

class OutputPin : public Pin {
 virtual void setPinValue(bool value) { pinA1 = true; }
 virtual bool getPinValue() const { return pinA1 };

Then I set out to find if I could use the compiler for my help in such a case. As usual Stackoverflow had question and answer about it. The answered marked as right is the ideal answer: No you cannot delete Pure Virtual Methods, fix your design. A bit further down showed the real answer: You can achieve something similar but it is not advised:

class InputPin : public Pin {
 virtual bool getPinValue() const { return pinA1 };
 virtual void setPinValue(bool value) { throw std::runtime_error("Cannot set value on input pin"); } 

Just encapsulate the breaking method in the private part of the class and no one will be able to use it. If the Older-You gets the idea of using it in some private part of your own implementation you still get the luxury of the exception

I like answers who say "You kind of can do it, but you shouldn't", because you get to learn the corner cases and tricks with which to shoot yourself in the foot some time later. I, like everyone else, like a corner trick to impress the girls. Of course some time later it bites me back, or just my Older-Me looks back with astonishment at such a pretentious idiot I was.

*EDIT* After thinking a bit more about it and talking with my friend about it, he came up with the idea that just hiding the method in a private part of the class is not enough to make it reachable. This is because if the class is called polymorphically the virtual dispatcher in run-time will still reach this hidden method.

The best way in the end is to make it private and do nothing.

TLDR; Redesign your architecture to not have broken interfaces.

Saturday, April 15, 2017

Firefox mouse-less addon workflow

Today I had some time to tweak my Firefox workspace and came up with an addon combo which might be useful for somebody. The combo's purpose is to enable internet navigation almost completely without mouse.

Normally I have many open tabs on Firefox, and when there were that many they become invisible and only reachable by some kind of scrolling. This sucked because I do not have the habit of being organized and grouping tabs by theme, although I should.

The scrolling problem is removed by accepting that the tab bar can be multi-row. There just happens to be a cool addon called Tabmix Plus which allows multi-row tabs. It brings lots of other functionality which I do not care. If anybody is interested I exported it's settings for further reference are available in this link. To import it just go to TabMix Plus's settings and import the file.

This enables me tab visibility and knowing where the Tab I wanted was relative to my current tab, I coudl use the Ctrl-PgDn/PgUp trick switch tabs. The thing is, I have normally 30 tabs or more. Going one-by-one until my desired tab took sweet time. Also along the way it loaded all the tabs that were just lazy loaded.

I knew that there was a shortcut to go directly to a tab number. The problem is that this shortcut only goes up to the 9th tab. I found a very basic, but functional plugin to allow me to go to any tab number, "GoTo Tab Number". The plugin is very basic and with Ctrl-Shift-O I am able to raise an ugly dialog to write the tab number. Even so yet another problem came up: How do I know the tab number in 30 tabs?

I found yet another slightly abandoned addon caled "TabNumber". This one, I felt I had to modify it as the position of the numbers overlaying the tab just looked out of place. It took me quite long to adjust and find what I was comfortable with. This was because my addon development workflow to reload the changes was quite shitty:
  • Make changes to the extracted .xpi.
  • Zip the plugin contents into a xpi.
  • Copy the plugin to the where Firefox expected it.
In the end it worked and I created a repository in github to store it. I tried to contact the author about it and if he wants he can publish my changes although I doubt he will. The changes are GPL because the license is GPL. To install it, as stated in the README:
  • git clone
  • cd TagNumber
  • zip -x "TagNumbersPTSN.xpi" -r "TagNumbersPTSN.xpi" .
  • Install the .xpi manually on Firefox.
For the navigation the VimFX plugin makes the honors. Very clean and I have yet to have any annoyance with it. My favourite and most used functionality is the F key to get a key combination for each possible link. When you type the appropriate key combination, firefox follows the link.

Normal Ctrl-LeftArrow allows to return to the previous page, and O allows the address bar to get focus with all current content selected. This way you can just start typing and what was there gets deleted automatically if you do not care about it. The Address bar also works as a search bar which makes it basically the only text are you need.

libpurple for facebook chat

Nowadays I use Facebook's messenger for about everything, to the point that even in the phone It has mostly replaced the SMS.
With this in mind, I would like a client for Linux that would natively connect to the Facebook Messanger. The intent is that I am not distracted by other Facebook content while doing more serious stuff. Also the web interface of messenger is bloody heavy.

Some time ago I used the facebook client of Thunderbird but it has since stopped working. I tried following the bugzilla ticket with no success. I even offered myself to pay to the author of the patch mentioned in the bugzilla ticket but when I made the offer I stopped getting any replies. I would have done it myself but....javascript... is definitely not the language I master. I feel Javascript is script kiddie language so it makes the will to dive into the code even lower. I am full of shit of course.

Sad, I went around for some more time using the web client of messenger until I found that there is a library, which makes Pidgin messenger compatible with Facebook's messenger. There is even an (outdated) Debian repository which makes the library installation painless (instructions here).

I used the library in the repository for some time but unfortunately it is not updated very often and recently the library broke with the error:
 Null value for $.viewer.message_threads.sync_sequence_id #306

For some weeks I was "sad" again as I did not want or know how to integrate the library build from source in my Ubuntu machine. This weekend I finally got some more time and bit the bullet, going on to find a fix for the problem. I found the solution thanks to the fast response from dequis and now leave here the instructions so that I can also remember when the time comes to update it again.

The following instructions to build dequis libpurple facebook plugin:

  • sudo apt-get install autogen autoconf libtool
  • git clone
  • cd purple-facebook
  • sudo apt-get install libpurple-dev libjson-glib-dev mercurial
  • ./
  • make
  • mkdir -p ~/.purple/plugin
  • cp pidgin/libpurple/protocols/facebook/.libs/ ~/.purple/plugins
I know there is a possibility to generate the debian packages, and it is probably as easy as, the previous steps, but I do not want to maintain any debian packages. Because of this  the library is now in an obscure part of my HOME directory which pidgin picks up, hihi.

Ok, ok. While I was writing this post I found it stupid to not write how to generate the debian package and gave it a try. Say you love me in the comments if it was useful: 

  • git clone
  • cd purple-facebook 
  • debuild -b -uc -us
  • cd ../
  • sudo dpkg -i purple-facebook_0.0.0-1_amd64.deb

Now I have a confession to make. I don't like Pidgin because it is slightly ugly. I use thunderbird and enjoy it, so my secret is that I would like to use this plugin for thunderbird. I set out to search a plugin for Thunderbird which would enable compatibility with libpurple and found an old plugin called "Additional Protocols for Thunderbird".
I tried to install it but it fails the compatibility check of my current Thunderbird. I even tried to be too clever, and downloaded an extension to Disable Compatibility check, but I couldn't understand if the plugin was broken or if I did not know how to use it.


Friday, March 16, 2012

How to Setup and run Ritchieduino

Hi again. The reason of this post is to show how to successfully set up the a developing environment to use Ritchieduino library. I will also assume some form of Arduino board available, running in Windows, even though any other platform will have just some adjustments. If you use for instance the ICSP mode you are on you own regarding avrdude.

To set up the environment the following software packages are required:
  • Ritchieduino package needed files which are here.
  • The latest winAVR, this is important because it provides the tools and configuration of the AVR-GCC tool chain. Don't forget to allow winAVR setup to change the your PATH variable so that the AVR eclipse can find it automatically. Please note that there may be a bug in which the setup destroys your pre-existing path. If such thing happens please go to the directory in which winAVR is installed and look for a file named path1.log which contains your previous PATH variable so that you can fix it.
  • The latest Classical Eclipse IDE, to use as the development environment. Before downloading it is necessary to check whether the Java virtual machine is 32 or 64 bits. To do that just make sure  Java is installed typing java -version. If the command successfully runs and there is not any mention of 64 bit in the output than it is a standard 32 bit Java Virtual Machine and you should download the 32-bit version of Eclipse. If the command fails it is possible you don't have java installed and you must install it from here. It is advisable to have the 32 bit Virtual Machine or there may be problems with RXTX plugin for Eclipse that allows the Serial console functionality

The following steps should be taken in order to make sure everything is set up correctly. The steps which are probably optional will be detailed for sake of completeness. More experimented users will probably be able to skip some steps.

  1. (Optional) This first step is to install the Arduino Windows drivers for the first time, so most users will probably be able to step over this. It is also really simple. The Arduino board should be connected to the USB port and  the"Windows key+r" be pressed at the same time. On the Run dialog write "devmgmt.msc. On the device manager window try to find "Ports (COM & LPT)". Under that is "Arduino UNO (COMxx)", where xx denotes any assigned port number (normally COM7). Right clicking and selecting "Update Driver Software" should open a dialog. Select "Browse my computer for driver software", the appropriate location for the Ritchieduino package should be selected. The drivers are in "\drivers\.inf". Hopefully the driver is successfully installed and the next steps can be taken.
  2. (Optional) The installation of winAVR is pretty much straight forward just keep in mind the problem with the PATH variable mentioned above.
  3. (Optional) The most critical and time consuming task is to install and configure the Eclipse IDE with everything a programmer needs to be productive.The first thing to be done after downloading Eclipse IDE is to extract it to somewhere. After that, it open it for the first time.
  4. (Optional) Upon starting Eclipse for the first time a directory should be selected where the projects will stay. Eclipse calls this directory workspace. It is advisable to either leave the default directory set or create one specifically for this purpose, so that everything stays organized in one place without future conflicts, like with Git. The check box  "Use this as the default and do not ask again" should also be activated so that any accidental change doesn't break the set up. Upon proceeding you will be officially inside the Eclipse IDE and will be greeted by a "Welcome to Eclipse" screen. Congratulations!
  5. (Optional)  In this step necessary plugins will be installed in Eclipse, specifically the CDT, AVR, EGit, RXTX and Target Management Terminal.
    1. So on the menu bar select "Help->Install New Software". When the new dialog appears, click on "Add" which will open a dialog to add a repository. In this case, the repository to add is the AVR plugin. The name can be anything, but for the sake of completeness it will be named "Avr Eclipse Repository". The location will be "". Note that this address can change, although unlikely.
    2. On the combo list "Work with:" the "Avr Eclipse Repository" should be selected. It is likely that a "Pending" will appear on the list below. It can be a while, as Eclipse is fetching the available plugins. 
    3. Afterwards the "AVR Eclipse Plugin" should show on the list and its check box should be activated. 
    4. Pressing "Next" twice and followed by accepting the license should highlight "Finish" which should be pressed to start the plugin installation process. 
    5. You should wait while software installs. During the installation it is possible that Eclipse warns you of unsigned content and you should continue the process. If you need re-assurance follow to the original AVR plugin site and check that the address supplied before matches the recommended in the site.
    6. Upon request restart Eclipse IDE.
    7. The process of installing another plugin will be repeated now for CDT, the component that adds general C/C++ functionality to the IDE.
    8. Following the Help->Install New Software" receipt again, select on the combo list "Work with:" the "All Available Sites".
    9. Below the combo box should be an empty text box which acts as a filter. There the text "C/C++ Development Tools" should be pasted. Note that if you manually write it, Eclipse IDE may hang because it is filtering the whole plugin list aggressively character by character. Even so it might hang some time.
    10. Tick only the "C/C++ Development Tools" and proceed like in the AVR plugin installation (step 5.5). In the end of this step it would already be possible to target AVR hardware but regarding Ritchieduino some more steps are required.
    11. Again the process will be repeated, only now to install eGit which enables the cloning of the Ritchieduino repository in Github.
    12. To install EGit the instructions are similar to the ones in step 8 just that this time the filter should be "Eclipse EGit" proceeding with similar previous steps to install it.
    13. Similar to the procedure in Step 5.1 followed to add the AVR plugin, RXTX repository is required to be added. To do so add "" selecting afterwards RXTX 2.1-7r4 and installing it. 
    14. This time the procedure is similar to the installation of EGit, just write in the filter "Target Management Terminal" and proceed with the install.
    15. The plugins installations are complete and it is time to start cloning the repositories
  6. In this section the Ritchieduino clone will be done.
    1. It is possible to clone the Ritchieduino repository by following "File->Import->Git->Projects from Git->Next" and then a dialog will ask you to select the repository. For that click "Clone"  and a dialog with lots of text boxes will appear. 
    2. Fortunately only the URI one is needed and in it input "git://" and all other fields will automatically be set. Clicking "Next" will connect to the repository and Master branch will be already pre set. Continue with "Next" and "Finish" the repository will be set up. The dialog will close.
    3. If the repository was successfully added, the Ritchieduino repository should now be selected proceeded with "Next".
    4. Check that the "Import existing projects" radio button is set and just press "Next", and "Finish" in the next page.
    5. If everything has gone well the Ritchieduino default Projects should have been imported, making one more step complete.
  7. In the following steps the AVR environment will be configured according to the required AVR target chip.
    1. Starting by going to to the menu bar "Window->Preferences".
    2. In the opened dialog collapse the "AVR" tree-list and select "Paths".
    3. If the winAVR installation was successful all the paths should be already pre-set, with the exception of the Atmel Part Description Files. In the list find "AVRDude" and click on "Edit".
    4. On the "Change Path for AVRDude" change the "Path Source" to "Custom". Afterwards select "Browse...". Selecting the Ritchieduino Software Package folder that was previously downloaded is all that is necessary. 
    5. Back in "Preferences", now looking again at the tree list, and under "AVR", select "AVRDude".
    6. Mark  "Use custom configuration file for AVRDude" and "Browse", selecting again the Ritchieduino Software Package folder.
    7. Now on the "Programmer configurations" press "Add..." .
    8. A big dialog should open, and in the "Configuration Name" Ritchieduino should be written.
    9. The "Description" can be anything.
    10. On the "Programmer Hardware" list, "Arduino" should be selected.
    11. The "Override default port (-P)" text box should be set with \\.\COM7. (Without the dot).As mentioned earlier it can be other COM number, but normally its 7.
    12. The "Override default baudrate (-b)" should be 115200.
    13. Proceed with "Ok" until the "Preferences" dialog closes.
  8. Now there is a quite boring task that has to be repeated for all the libraries that you are going to use in Ritchieduino, but in fact is crucial and can't be defaulted, which is setting the target chip. For the sake of simplicity only the steps for RitchieduinoCore.
    1. On the menu bar go to "Window->Show View->Project Explorer"
    2. On the Project Explorer left click on the RitchieduinoCore project and select "Properties".
    3.  On the tree list select "AVR->Target Hardware".
    4. On the "MCU Type" you should select your target chip and in the "MCU Clock Frequency" the frequency. For instance for the Arduino Uno, the type is "ATmega328p" and the frequency "16000000".
    5. This whole step should be repeated for every library you wish to use once and every new project you decide to create. If this step is not taken your applications may not work correctly.
  9. There is a project ready to try which is the RitchieServer, an example ready to run. It is important that step8 is done on this project also. Note that the Ethernet shield is necessary.
    1. Go to the menu bar and select "Window->Open Perspective->Other". On the dialog that appears select "C/C++".
    2. On the Project Explorers' tree list collapse and double click "RitchieServer->main.c" so as to see what is being executed.
    3. Care should be taken so that the network settings in the source file match the desired local network.
    4. To build this project you only need to go to the Project Explorer, right click RitchieServer and select "Build Project".
    5. It will take some time in the first run but should be relatively fast afterwards (faster than the Arduino IDE).
    6. Upon reading "**** Build Finished ****" on the console vie.
    7. If everything has been successful it is now possible to upload to the board.
    8. To upload the program just select the RitchieServer project in Project Explorer and click on a green AVR icon on the tool bar in the upper part of the Eclipse window. Alternatively it is possible to do "Ctlr+Alt+U"
    9. After the upload to see the results of the Serial port data doing "Window->Show View->Terminal" is needed.
    10. After the terminal shows in the tabs in the view sub window there is a small button called "Settings".
    11. In the dialog that pops up the "Connection Type:" should be set to "Serial" and the "Port" should be set to COM7 or if different to the relevant one. The baud rate should be noted in future uses. Pressing "Ok" closes the dialog.
    12. Pressing the small green "Connect Button" connects to the serial device.
  10. If everything has been successfully executed the terminal should now be printing, for the case of RitchieServer, "Comunications Initted".
That is all that is needed to set up Ritchieduino. There will be another post on how to make a Hello World be printed in the Serial output.