Subject: [bug#34863] [WIP] syscalls: Add loop device interface.

From: Danny Milosavljevic <[email-masked]>
Date: Fri, 15 Mar 2019 17:13:06 +0100

> +(define (set-loop-device-status loop-file status)
> +  (let ((buf (make-bytevector sizeof-loop-info64)))
> +    (apply write-loop-info64! buf status) ; TODO: Be more user-friendly.

I don't know how instantiate a C structure given an assoc list.  Help?