Using (unsupported) SMB shares for Time Machine

Yesterday, after setting up my Samba NAS based on a dual-Atom MSI Wind Box, I fought against Time Machine, which refuses to use a shared folder as a backup disk.

So after a long struggle, I found this forum post which make everything work.

DISCLAIMER: this use of Time Machine will be unsupported by Apple, so use it at your own risk, warranty is void, and so on.

Terminal access is required.