ck_ht_entry_key_direct(3) on Linux
The text d8df31d39e1d, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 9 (Stretch), Debian 8 (Jessie) shipped it. The page shows this text now.
return key value as specified in hash table entry