Hi Dominic,

On Wed, 22 May 2019 at 13:53:07 +0100, Dominic Raferd wrote:
> Thanks Arno, I think it is Debian really (rather than Ubuntu), but I
> couldn't see where to ask except here. Will dig some more.

For Debian you could file a bug against the ‘cryptsetup-initramfs’
package, see https://tracker.debian.org/pkg/cryptsetup and
https://www.debian.org/Bugs/ .

(‘Severity: wishlist’ I guess; at least your custom patch not applying
anymore isn't hinting at a regression.)

Also FWIW we (Debian packaging team) have native support for unlocking
multiple devices at early boot stage with a single passphrase prompt,
see /usr/share/doc/cryptsetup-initramfs/README.initramfs.gz and
/usr/share/doc/cryptsetup-run/README.* .  If that doesn't cover your
workflow then please visit the above links and file a wishlist bug :-)

Cheers,
-- 
Guilhem.