removable drive access portal

[Be-ing]

Some applications present GUIs that treat removable drives separate from other parts of the filesystem. Here is an example from Mixxx, and the relevant code:

Currently, this can't work in a Flatpak without specifying

  - --filesystem=/media
  - --filesystem=/run/media

The file picker portal isn't a solution for this because the application can't determine if there are any devices available to ask the user for permission to use.

See also:
flatpak/flatpak#2713
mixxxdj/mixxx#12860

[Mikenux]

If it's about getting files, giving access to the USB storage device makes no sense because it means possibly giving access to files that are irrelevant to the app. For this, as indicated in other issues that you have mentioned, there is the file chooser which allows a finer selection of files. Additionally, I believe the files can be restored by the app, as the app keeps access to the files. So what is the real problem here?

[Be-ing]

The problem is that the application can't determine if there even are USB storage devices plugged in, so there's no way to prompt the user for permission to access them.

[Mikenux]

I just understood !

What is needed is for a portal to detect when files or folders come from a dynamic location (USB storage, network mount). How to tell this to the app is to see.

[TingPing]

So I guess this would be broken down into a few tasks:

• xdg-desktop-portal monitors for portable drives being attached (UDisks?)
• A new portal API is added that has a signal applications can listen to, and a method to request access
• The frontends need to present a dialog to the user to allow it. Permissions could be tricky, we both don't want to spam dialogs but also not be too eager to mount things we shouldn't.
  • Probably tie the access to partitions, so if a user reformats a drive access is lost
• Then the directory gets mounted in the sandbox

[Mikenux]

The frontends need to present a dialog to the user to allow it. Permissions could be tricky, we both don't want to spam dialogs but also not be too eager to mount things we shouldn't.

If possible, it would be best to monitor which paths the application has access to, avoiding requesting access.

It would rather be:

• User adds files or folders from a removable drive and the portal is aware of this.
• When the portal knows that removable media is plugged in and mounted, it checks if an application has file or folder permissions.
• The portal can signal that these files and folders are available for access.

[TingPing]

If possible, it would be best to monitor which paths the application has access to, avoiding requesting access.

How is it possible to know a path that doesn't exist yet?

You mean requiring a well known toplevel path?

[Mikenux]

Something like this, non-exhaustive:

1. When adding files or folders to the app (file chooser, file manager, drag and drop), the portal knows that they are on a dynamic location (USB storage, network mount).
2. The portal stores information that a given path belongs to a dynamic location and which one (for the respective app).
3. The portal automatically allows the app to subscribe to the signal which will tell it that the files or folders are available. At least, if there is no objection to the fact that an app can automatically know that a file or folder comes from a dynamic location.
4. When the dynamic location is mounted by the system, the monitor is aware of it, checks which apps have permission to access files or folders at that location and sends the signal to the apps.
5. Apps can access the files and folders they have access to.

[TingPing]

In my mind a primary use-case for this feature is to plug in a new portable drive and let an app use it.

[Mikenux]

Yes, but this is about files. I don't think offering apps the ability to request access to a USB storage device - i.e. "Allow access to [USB_Storage_NAME]?", therefore to access all its files, is a good idea. The fact is that even if we ask for permission, if the user wants to use their USB storage, they will allow access to it, thus giving all the files to the app, without really having the choice.

In contrast, we have the file chooser which allows users to select only the files they want to give to an app: a file, a selection of files, a folder, or all content of a USB storage device (by selecting it in the file chooser).