Set a minimum sector lifetime

Author: Stebalien

extern/storage-fsm/states_sealing.go

@@ -159,6 +159,13 @@ func (m *Sealing) handlePreCommitting(ctx statemachine.Context, sector SectorInf
 		return ctx.Send(SectorSealPreCommit1Failed{xerrors.Errorf("handlePreCommitting: failed to compute pre-commit expiry: %w", err)})
 	}
 
+	// Sectors must last _at least_ MinSectorExpiration + MaxSealDuration.
+	// TODO: The "+10" allows the pre-commit to take 10 blocks to be accepted.
+	if minExpiration := height + miner.MaxSealDuration[sector.SectorType] + miner.MinSectorExpiration + 10; expiration < minExpiration {
+		expiration = minExpiration
+	}
+	// TODO: enforce a reasonable _maximum_ sector lifetime?
+
 	params := &miner.SectorPreCommitInfo{
 		Expiration:   expiration,
 		SectorNumber: sector.SectorNumber,