A program that allows to run other programs only after a set of questions have been correctly answered
flo-check-homework presents one or more questionnaires to the user. Once all questions have been answered, and if the score exceeds a predefined threshold, a special button is enabled. When pressed, this button launches the program (with optional arguments) that was specified on flo-check-homework’s command line. For instance, the following command:
flo-check-homework -- prog arg1 arg2 arg3
will start flo-check-homework without any option and allow the pupil to run, if the questionnaires receive good enough answers, the program ‘prog’ with 3 arguments: ‘arg1’, ‘arg2’ and ‘arg3’. To see all available command line options, you may run:
In flo-check-homework’s graphical user interface, a “magic word” button allows one to bypass the test in case the pupil has already done his homework in another way. It also makes it possible to exit the program immediately.
Indeed, flo-check-homework refuses to quit immediately unless option -e was given or a sufficient score was obtained; this is done so as to avoid the children validating the whole questionnaire with incorrect answers only to get corrections that they can blindly copy after rerunning the program. For the same reason, some of the question generators purposedly don’t remember incorrect answers, in contrast with the initial design.
Since version 0.10.0, there is a new feature called super magic word that gives, if properly entered, a super magic token which is valid for a limited amount of time (see The super magic word below). This allows more freedom to run the available games once the token has been granted. Since my goal is definitely not to use technical means in order to limit the pleasure children can have with games, a successful work does grant a super magic token, just as if the super magic word had been entered.
Version 0.10.0 also introduced the AllowExitBeforeChild configuration file parameter in the General section, defaulting to 1. If set to 0, quitting is also forbidden as long as the program specified on the command line (“desired program”) is running—assuming it was started from flo-check-homework. This can be useful with kids misusing a super magic token to run dozens of games simultaneously.
Currently, the questions are designed to help consolidate simple additions, substractions, multiplications, euclidian divisions and conjugations of French verbs. The questionnaires are built at run-time and can be customized to some extent via a configuration file (~/.config/Florent Rougon/flo-check-homework.ini on Unix-like systems). It is easy for a Python programmer to add new question generators, questionnaires or subquestionnaires.
The ItemGenerator class, which is the basis for many question generators, has the following properties:
- starts with items that have been incorrectly answered in previous sessions
- cycles through all items but does not yield an item that has already been seen in the current session (unless all items have been seen)
- Seen objects (used to remember which items of a given type have been seen in the current session) can be shared between several question generators. This avoids asking the same question twice in case several question generators are likely to generate the same question.
It is possible to setup launcher scripts that call flo-check-homework with the appropriate parameters depending on the script (and parameters passed to the script). The flo-check-homework-decorate-games program from the ‘tools’ directory is provided to help automate such a setup. Basically, you write a list of programs/games in an XML file which we’ll call DATAFILE for the sake of the example. You may look at flo-check-homework-decorate-games.xml from the tools/flo-check-homework-decorate-games folder or run ‘flo-check-homework-decorate-games –help’ for an example of such a file. Once you have a proper DATAFILE, run the following command as a user who has permission to write to /usr/local/games:
# flo-check-homework-decorate-games /path/to/DATAFILE
This will create an appropriate launcher script in /usr/local/games for every program listed in DATAFILE. If /usr/local/games is prepended to the system PATH, then the launcher scripts will take precedence over the corresponding game executables when a user tries to run a game, unless a full path to the game executable is specified. So, when using wrapper scripts, the call chain looks like the following:
--> wrapper script 'foo' called with arguments arg1 ... argn --> flo-check-homework [some options] -- foo arg1 ... argn --> foo arg1 ... argn (or '<launcher> foo arg1 ... argn' if using the ProgramLauncher feature)
where each arrow indicates a different process. “some options” typically contains -p (–pretty-name) to tell flo-check-homework the “pretty name” of program ‘foo’, for displaying in the graphical user interface.
The above trick, based on the PATH environment variable, also works if the game is started from the freedesktop menu, because freedesktop .desktop files usually don’t specify a full path to the executable (when they do, the only recourse is to fix the .desktop file manually and report a bug to the game in question). The format of .desktop files is described in the Desktop Entry specification.
flo-check-homework-decorate-games has options to customize the paths such as /usr/games and /usr/local/games, as well as options to choose which locale to use when a launcher script starts flo-check-homework, and when flo-check-homework runs a game. See the output of ‘flo-check-homework-decorate-games –help’ for more information.
Since version 0.10.0, a new kind of magic word, creatively called the “super magic word”, allows one to run the decorated games more easily and transparently. When one chooses this function from the Magic menu (added in version 0.10.0) or from the toolbar, one is asked to enter the super magic word, similarly to the simple “magic word”. If the given answer is correct, a “super magic token” is granted that allows one to run all decorated programs (likely to be games) in a transparent manner. This special permission is valid for some time that depends on the super magic word that was given (see the source!). Once the token has been granted, it is possible to launch the predefined game from flo-check-homework’s GUI, as for a simple “magic word”. However, in order to run different games under the super magic token super powers, one should rather quit flo-check-homework first, otherwise the locking mechanism used to protect the QSettings against eventual corruption caused by several concurrent uses would prevent other instances of flo-check-homework from running normally, and therefore make it impossible to run other decorated games until the instance that is holding the lock is ended.
In short, the suggested use of this feature is the following:
Note: there is still some locking performed when flo-check-homework runs the decorated game “transparently” after finding out that the user has a valid super magic token. However, it is very short, the lock being released before the decorated game is started. Therefore, several decorated programs/games may be run concurrently this way, even though the corresponding flo-check-homework processes may block each other for a short time because of the locking performed in order to protect the QSettings.
In this mode, flo-check-homework uses a call from the exec*(2) family (execvp(2) in version 0.10.0) without forking beforehand. Consequently, it doesn’t consume any resource whatsoever once the decorated program is started, and the exit code returned is exactly the same as if the decorated program had been run without flo-check-homework intervening. This is why this mode is said to allow transparent execution of the decorated programs.
When flo-check-homework is started, it can operate in two distinct modes: either the graphical interface is displayed, or the program specified on the command line is automatically run. The former is called interactive mode and the latter transparent mode. Interactive mode is chosen if, and only if:
- the --interactive option has been given or;
- the ForceInteractive setting in the General section of the configuration file is equal to 1 or;
- the user has no valid super magic token.
The following software is required to run flo-check-homework:
- Python 3.1 or later in the 3 series;
- Qt 4.8 or later;
- PyQt 4.10.3 is known to work, version 4.9 should be enough and older versions will most probably not work with this version of flo-check-homework.
Version 0.11.1 of flo-check-homework has been tested on Linux with Python 3.5.1, Qt 4.8.7 and PyQt 4.11.4. It should work on any platform with the aforementioned dependencies installed, but trivial bugs are likely to pop up on non-Unix platforms as no test whatsoever has been done on them. Please report.
For installation instructions, please refer to INSTALL.txt.
flo-check-homework is maintained in a Git repository that can be cloned with:
git clone https://github.com/frougon/flo-check-homework
It is possible to run flo-check-homework from a clone of that repository, but two things that are not part of it have to be set up in order for everything to work properly:
- the flo_check_homework/images directory tree containing icons and “reward images” must be copied from a release tarball, otherwise there will be an error when all questions have been answered and the program tries to show an image;
- the .qm files (used for translations) that are relevant to your locale settings must be generated from the corresponding .ts source files; this can be done automatically with the Makefile shipped in the top-level directory of the Git repository, provided you have GNU Make (run ‘make’).
Since version 0.10.0, it is possible to tell flo-check-homework to use an intermediate launcher to start the desired program (game or whatever you want). This is done by setting ProgramLauncher in the configuration file to the name or path to the launcher executable. This results in a command where the value of ProgramLauncher is prepended to the command line for the desired program. Of course, if ProgramLauncher is empty or unset, no intermediate launcher is used.
This new feature can be used in a setup where for instance /usr/games does not have the executable bit set for the user running flo-check-homework, but does have it for a particular group which we’ll call gamers for the sake of this discussion. If you create a custom launcher program in C that uses the setgroups(2) system call to add the gamers group to the list of supplementary groups for the calling process before using execve(2) to run the desired program, then it becomes possible for the user to run the desired program through flo-check-homework even though it would appear to be impossible at first (of course, the launcher program is the one providing the required privileges here, and is also accessible to the user in such a setup).
The setup described in the previous paragraph requires a little modification to wrapper scripts, which by default check the executable bit of the program to run. In this case, the check would necessarily fail and should be skipped. Invoking flo-check-homework-decorate-games with the –no-exec-check option generates scripts that don’t perform such a check.
To be of any use, a launcher program as described above would need the CAP_SETGID capability on Linux. As a consequence, it would require great care in writing and installing. For a start, the GID of the group passed in the aforementioned setgroups(2) system call must not be something that unprivileged users can choose, and that group should have no more powers than being able to access /usr/games in a read-only manner. Additionally, the launcher program should be installed on a partition where unprivileged users have absolutely no write access, otherwise they could make a hard link to the executable that would defeat the purpose of a security update (this is a general issue to consider whenever using setuid or setgid executables or, as described here, programs with special capabilities—in the specific sense this word has for Linux, as documented in the capabilities(7) manual page). For all these reasons, and because of its obvious side effects (such as not being able to execute fortune(6) normally, if installed in /usr/games), this kind of setup should only be adopted if really necessary (not to mention the fact that it can be easily defeated; as announced in the title, it is a hack!).
Since flo-check-homework-decorate-games is currently only able to generate shell scripts, it is not expected to be of any use on platforms that cannot run them. This means that you can fill in questionnaires on these platforms but can’t expect to be able to run the desired program/games from flo-check-homework after a good enough work without some adaptation for such platforms. (For Windows platforms, one might use Cygwin or adapt flo-check-homework-decorate-games to generate batch files, or something else, let Windows experts decide in this matter…)
All images, as the rest of the package, are free according to the Debian Free Software Guidelines (DFSG-free for short). I wanted to use photos of angry-looking dogs easily found with Google Images, but unfortunately, they all appear to be non-free. If you have good suggestions of free software-licensed images to improve this program, please advise.