fix: remove dead sessions from target session list

When an iSCSI connection closes or a logout occurs, the associated
session was never removed from the target's Sessions map, and the
TSIH was never released back to the bitmap allocator. This caused
session and TSIH leaks over repeated connect/disconnect cycles.

Changes:
- Add removeConnectionFromSession() to properly clean up session
  when its last connection is closed
- Call session cleanup from handler() on CONN_STATE_CLOSE
- Convert iscsiExecLogout to a method and add session cleanup on logout
- Release TSIH in UnBindISCSISession to prevent TSIH bitmap exhaustion

Fixes #42

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pkg/port/iscsit/iscsid.go

@@ -357,6 +357,7 @@ func (s *ISCSITargetDriver) handler(events byte, conn *iscsiConnection) {
 			s.rxHandler(conn)
 			if conn.state == CONN_STATE_CLOSE {
 				log.Warningf("iscsi connection[%d] closed", conn.cid)
+				s.removeConnectionFromSession(conn)
 				conn.close()
 				IPMutex.Lock()
 				remoteIP := strings.Split(conn.conn.RemoteAddr().String(), ":")[0]
@@ -373,6 +374,7 @@ func (s *ISCSITargetDriver) handler(events byte, conn *iscsiConnection) {
 	}
 	if conn.state == CONN_STATE_CLOSE {
 		log.Warningf("iscsi connection[%d] closed", conn.cid)
+		s.removeConnectionFromSession(conn)
 		conn.close()
 		IPMutex.Lock()
 		remoteIP := strings.Split(conn.conn.RemoteAddr().String(), ":")[0]
@@ -491,7 +493,7 @@ func (s *ISCSITargetDriver) rxHandler(conn *iscsiConnection) {
 		case OpLogoutReq:
 			log.Debug("OpLogoutReq")
 			s.setClientStatus(false)
-			if err := iscsiExecLogout(conn); err != nil {
+			if err := s.iscsiExecLogout(conn); err != nil {
 				log.Warningf("set connection to close")
 				conn.state = CONN_STATE_CLOSE
 			}
@@ -559,7 +561,7 @@ func (s *ISCSITargetDriver) iscsiExecLogin(conn *iscsiConnection) error {
 	return conn.buildRespPackage(OpLoginResp, nil)
 }
 
-func iscsiExecLogout(conn *iscsiConnection) error {
+func (s *ISCSITargetDriver) iscsiExecLogout(conn *iscsiConnection) error {
 	log.Infof("Logout request received from initiator: %v", conn.conn.RemoteAddr().String())
 	cmd := conn.req
 	conn.resp = &ISCSICommand{
@@ -573,6 +575,7 @@ func iscsiExecLogout(conn *iscsiConnection) error {
 	} else {
 		conn.resp.ExpCmdSN = conn.session.ExpCmdSN
 		conn.resp.MaxCmdSN = conn.session.ExpCmdSN + conn.session.MaxQueueCommand
+		s.removeConnectionFromSession(conn)
 	}
 	IPMutex.Lock()
 	remoteIP := strings.Split(conn.conn.RemoteAddr().String(), ":")[0]
@@ -1018,7 +1021,7 @@ func (s *ISCSITargetDriver) scsiCommandHandler(conn *iscsiConnection) (err error
 		s.setClientStatus(false)
 		conn.txTask = &iscsiTask{conn: conn, cmd: conn.req, tag: conn.req.TaskTag}
 		conn.txIOState = IOSTATE_TX_BHS
-		iscsiExecLogout(conn)
+		s.iscsiExecLogout(conn)
 	case OpTextReq:
 		err = fmt.Errorf("Cannot handle yet %s", opCodeMap[conn.req.OpCode])
 		log.Error(err)

pkg/port/iscsit/session.go

@@ -334,6 +334,27 @@ func (s *ISCSITargetDriver) UnBindISCSISession(sess *ISCSISession) {
 	defer target.SessionsRWMutex.Unlock()
 	delete(target.Sessions, sess.TSIH)
 	scsi.RemoveITNexus(sess.Target.SCSITarget, sess.ITNexus)
+	s.ReleaseTSIH(sess.TSIH)
+	log.Infof("session %x unbound from target %s", sess.TSIH, target.SCSITarget.Name)
+}
+
+// removeConnectionFromSession removes a connection from its session.
+// If the session has no remaining connections, the session is unbound.
+func (s *ISCSITargetDriver) removeConnectionFromSession(conn *iscsiConnection) {
+	sess := conn.session
+	if sess == nil {
+		return
+	}
+
+	sess.ConnectionsRWMutex.Lock()
+	delete(sess.Connections, conn.cid)
+	remaining := len(sess.Connections)
+	sess.ConnectionsRWMutex.Unlock()
+
+	if remaining == 0 {
+		s.UnBindISCSISession(sess)
+	}
+	conn.session = nil
 }
 
 func (s *ISCSITargetDriver) BindISCSISession(conn *iscsiConnection) error {