Give a Flapak app read-write access to its own internal file system

[Bartłomiej Piotrowski]

On 31/01/2022 21.40, Olof Nord wrote:
> Hello Flatpak devs!
> 
> I have a demo application[1], which during initial startup, extracts 
> some archives inside the Flatpak.
> 
> Is there any flags/ways of giving the application write access to its 
> own internal file system?
> In my case to "/app/bin/resources".
> This folder does not exist during build, but is created at startup.
> 
> Currently, I receive the following error message during startup:
> "unlinkat /app/bin/resources: read-only file system".
> 
> The files are only relevant to the application itself, there is no need 
> to access them from outside.
> 
> I have found "--sandbox-expose" to expose read-write access to a file, 
> but this argument isn't valid as a finish-args, and using "--filesystem" 
> isn't really applicable as the folder exists only inside the Flatpak 
> itself (It also does not address the problem, I have tried).
> 
> Using Flatpak 1.12.4, flatpak-builder 1.2.2.
> 
> Any advice or further information would be greatly appreciated!
> 
> Cheers,
> Olof Nord
> 
> [1]https://gitlab.com/olof-nord/go-astilectron-flatpak-demo 
> <https://gitlab.com/olof-nord/go-astilectron-flatpak-demo>

As far as I know, /app is read-only except for the extra-data modules, 
which can extract data to /app/extra during installation. There is no 
solution to that, it's by design.

A possible workaround is extracting files to $XDG_DATA_HOME, but I 
assume you would need to change your app to look for the data there.

Bart