[sane-devel] Invalid argument (status 4) when calling sane_start

[Peter Gebauer]

Hi!

> The v4l backend supports only a few modes so you have to select the correct ones to get a image.

So it's the v4l settings that are wrong or the SANE settings?

There's a couple of things I'd fix with the v4l backend

1) Default (startup) mode must be valid and supported so a user can 
sane_start() with the default settings. It makes no sense to put the device 
in "broken mode" at startup.

2) Unsupported modes should not be listed. Why whould you even list 
options/modes that aren't supported by the backend? Nobody wants a 
SANE_STATUS_INVAL so nobody will set an unsupported mode anyway. Any modes 
not supported should be removed from the options.

If your sane_control_option didn't give an error then that mode should be 
considered valid and usable setting. This will remove the unwanted surprise 
when calling sane_start() and it will remove the guess work trying to figure 
out what option is breaking the sane_start() call.

I'll look at the v4l backend, but fixing it to work properly would be a 
major detour from my project. The idea of allowing SANE to use v4l devices 
is great, it feels generic and... cool. :)

/Peter