modloader, along with it's companion modmanager, allow you to enable and disable of loading of shared libraries from /opt/etc/preload.d/ into the DJI glasses process.
Install a mod through package management or place your shared library into /opt/etc/preload.d/lib${your_mod_name}.so.
Then, to enable your_mod_name on the DIY GUI process run the following:
modmanager enable diy_glasses your_mod_name
To later disable it run:
modmanager disable diy_glasses your_mod_name
To list enabled mods for DIY GUI run:
modmanager list diy_glasses
Note that most packages will probably enable their respective mod for you by default on install.
Shortcuts
Since the DIY GUI has different process names on V1 and V2 Goggles the following shortcuts are available for you:
- diy_glasses - dji_glassess on V1 and dji_gls_wm150 on V2
- fpv_glasses - dji_glasses on V2
This simply allows you to inject your shared library into the vendor's service processes, what you do from there is up to you. You could:
- Use function overriding to replace any function calls for any other shared libraries with your own implementations
- Use your shared library constructor and destructor methods to run code before the vendor process starts or at shutdown
See the debug menu enabler for a full example of simple GUI lib method replacement (a NOP in this case) including a Makefile that will produce a complete .ipk for you.
In addition to the injectable library itself, you will also need to take care to update all the files in ipk/control/ with appropriate values for your library. Note that the debug menu enabler project uses a dinit unit to allow the user to toggle the mod via configurator, located at ipk/data/opt/etc/dinit.d/tweak-enable-debug-menu and enables that unit during postinst.
Note: in order to better deal with memory pressure issues on V2 Goggles the latest versions of modloader only target the dji_glasses/dji_gls_wm150 processes. If you as a developer need to preload over some other service then please contact the fpv.wtf team or open an issue on this repo.
Packages can include commands to be executed in the main menu by populating a .desktop file in /opt/share/applications/ with the Name, Exec, Icon and (custom) Icon_Active keys being respected. Icon and Icon_Active are optional.
When your application needs to take over the framebuffer it should do so by launching a dinit unit with an Exec value like dinitctl start my-unit-name. An optional fbwrapper utility is included to aid in starting and stopping the DJI glasses process.
See the examples directory for a .desktop file and dinit unit.
DJI's services (i.e. when you start something with setprop dji.something_service 1) are managed by Android init, which only reads it's config files once during bootup from the / ramfs before we ever have a chance to modify them.
Thus, to inject shared libraries into the various services, we move the service binaries out of place (in the loopmount /system image) and replace them with symlinks to modloader.
When init executes the symlink, modloader determines the executed binaries name, inspects the folder /opt/etc/preload.d/${service_binary_name}/ for symlinks to files to load and populates LD_PRELOAD according to .so-s found in an alphabetic order. It then proceeds to call the original service binary by appending "_original" to the name determined earlier.
When mods are found for a binary, a final entry to LD_PRELOAD is appended for libmodloader_final.so, which gets loaded last after any other libraries, and clears the processes LD_PRELOAD environment variable. This is done to ensure any modifications don't get loaded needlessly into DJI's excessive shell spawns.