As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB, RECEIVED MESSAGE SMOKE AFT CARGO SMOKE. CREW DISCHARGED AFT CARGO FIRE EXTINGUISHER. RETURNED TO BOS AND LANDED WITHOUT INCIDENT. NO INDICATION OF FIRE OR SMOKE UPON INSPECTION OF CARGO COMPARTMENT. MAINTENANCE TROUBLESHOOTING REVEALED NO DISCREPANCIES.