Room for service personnel in a port (7)
I believe the answer is:
messina
'port' is the definition.
(I know that Messina is a port)
'room for service personnel' is the wordplay.
'room' becomes 'mess' (mess is a kind of room).
'for' says to put letters next to each other.
'service personnel' becomes 'ina' (I can't explain this - if you can you should believe this answer much more).
'mess'+'ina'='MESSINA'
'in a' acts as a link.
Can you help me to learn more?
(Other definitions for messina that I've seen before include "Sicilian port" , "City in Sicily" .)