[fprint] fprintd : debug for raw image data and log file

[Bastien Nocera]

Hello Dave,

On Mon, 2019-08-19 at 12:04 +0800, Dave.Wang wrote:
> Dear,
> 
> As I knew, the daemon program named fprintd can not get the image
> data and
> the corresponding debug messages while enrolling and verifying, only
> the
> tools in libfprint/examples can get the debug image.

That's on purpose, the debug image is security sensitive data.

> However, we need the debug message log and the image raw data in real
> time
> to debug why our customers get errors.

The debug message log can be turned on by passing G_MESSAGES_DEBUG=all
to the fprintd daemon in its .service file.

> Is it possible for libfprint to provide a method to deliver the debug
> message and the raw 16 bit image data to fprintd and also make
> fprintd save
> the log files and image in real time?

I would strongly recommend that you use specific test applications
rather than the very generic fprintd when debugging a capture problem.

Though still not very practical, the libfprint build system creates a
Flatpak of the demo application. For example, clicking on the green
tick for the 1.0 release in gitlab:
https://gitlab.freedesktop.org/libfprint/libfprint/commit/823f2c1067a27deae4153dd9ece6ce24bedc0680/pipelines?ref=master

Click on the download icon, select "Download Flatpak master artifacts",
install the bundle.

Then as root, run "chown" on the /dev/bus/usb/ node that corresponds to
the USB device (that won't be necessary once Flatpak has the necessary
support for accessing USB devices).

You can now launch the demo application. The Flatpak bundle is also
generated for work-in-progress builds.

Cheers