> I think you can use ‘call-with-output-file’ for DEVICE no?

Sure.

> No: this would import the host Guile’s (ice-9 binary-ports) module into
> the guest, thereby making the result dependent on the Guile version
> being used “outside”.

Ok got it.

> Could you send an updated patch?

You'll find the updated patch attached.

Thanks for your fast review !

Mathieu