virtcontainers: share the agent's client between factory's VM and sandbox

When agent is configured as longLive, the VM's agent created
by factory will not close it's client once it connected, thus
the sandbox's agent cannot re-connect successfully.

Sharing the agent's client between VM's agent and sandbox
can fix this issue.

Fixes: #995

Signed-off-by: fupan <lifupan@gmail.com>

virtcontainers/agent.go

@@ -152,6 +152,9 @@ type agent interface {
 	// get agent url
 	getAgentURL() (string, error)
 
+	// update the agent using some elements from another agent
+	reuseAgent(agent agent) error
+
 	// createSandbox will tell the agent to perform necessary setup for a Sandbox.
 	createSandbox(sandbox *Sandbox) error
 

virtcontainers/hyperstart_agent.go

@@ -964,6 +964,17 @@ func (h *hyper) getAgentURL() (string, error) {
 	return "", nil
 }
 
+func (h *hyper) reuseAgent(agent agent) error {
+	a, ok := agent.(*hyper)
+	if !ok {
+		return fmt.Errorf("Bug: get a wrong type of agent")
+	}
+
+	h.client = a.client
+
+	return nil
+}
+
 func (h *hyper) setProxy(sandbox *Sandbox, proxy proxy, pid int, url string) error {
 	if url == "" {
 		return fmt.Errorf("invalid empty proxy url")

virtcontainers/kata_agent.go

@@ -537,6 +537,17 @@ func (k *kataAgent) getAgentURL() (string, error) {
 	return k.agentURL()
 }
 
+func (k *kataAgent) reuseAgent(agent agent) error {
+	a, ok := agent.(*kataAgent)
+	if !ok {
+		return fmt.Errorf("Bug: get a wrong type of agent")
+	}
+
+	k.installReqFunc(a.client)
+	k.client = a.client
+	return nil
+}
+
 func (k *kataAgent) setProxy(sandbox *Sandbox, proxy proxy, pid int, url string) error {
 	if url == "" {
 		var err error

virtcontainers/noop_agent.go

@@ -184,6 +184,11 @@ func (n *noopAgent) reseedRNG(data []byte) error {
 	return nil
 }
 
+// reuseAgent is the Noop agent reuser. It does nothing.
+func (n *noopAgent) reuseAgent(agent agent) error {
+	return nil
+}
+
 // getAgentURL is the Noop agent url getter. It returns nothing.
 func (n *noopAgent) getAgentURL() (string, error) {
 	return "", nil

virtcontainers/vm.go

@@ -319,6 +319,10 @@ func (v *VM) assignSandbox(s *Sandbox) error {
 		return err
 	}
 
+	if err := s.agent.reuseAgent(v.agent); err != nil {
+		return err
+	}
+
 	// First make sure the symlinks do not exist
 	os.RemoveAll(sbSharePath)
 	os.RemoveAll(sbSockDir)