proxy: fix up the vsock interface

- don't try to create a `FileConn` because the Go library sees through
  the scam and rejects it
- explicitly keep a reference to the `ctl` file just in case the GC
  decides its dead and should be closed.

Signed-off-by: David Scott <dave.scott@docker.com>

alpine/packages/proxy/main.go

@@ -8,53 +8,57 @@ import (
 	"os"
 	"libproxy"
 	"strings"
+	"vsock"
 )
 
 func main() {
 	host, port, container := parseHostContainerAddrs()
 
-	err := exposePort(host, port)
+	ctl, err := exposePort(host, port)
 	if err != nil {
 		sendError(err)
 	}
-	p, err := libproxy.NewProxy(host, container)
+
+	p, err := libproxy.NewProxy(&vsock.VsockAddr{Port: uint(port)}, container)
 	if err != nil {
 		sendError(err)
 	}
+
 	go handleStopSignals(p)
 	sendOK()
 	p.Run()
+	ctl.Close() // ensure ctl remains alive and un-GCed until here
 	os.Exit(0)
 }
 
-func exposePort(host net.Addr, port int) error {
+func exposePort(host net.Addr, port int) (*os.File, error) {
 	name := host.String()
 	log.Printf("exposePort %s\n", name)
 	err := os.Mkdir("/port/"+name, 0)
 	if err != nil {
 		log.Printf("Failed to mkdir /port/%s: %#v\n", name, err)
-		return err
+		return nil, err
 	}
 	ctl, err := os.OpenFile("/port/"+name+"/ctl", os.O_RDWR, 0)
 	if err != nil {
 		log.Printf("Failed to open /port/%s/ctl: %#v\n", name, err)
-		return err
+		return nil, err
 	}
 	_, err = ctl.WriteString(fmt.Sprintf("%s:%08x", name, port))
 	if err != nil {
 		log.Printf("Failed to open /port/%s/ctl: %#v\n", name, err)
-		return err
+		return nil, err
 	}
 	_, err = ctl.Seek(0, 0)
 	if err != nil {
 		log.Printf("Failed to seek on /port/%s/ctl: %#v\n", name, err)
-		return err
+		return nil, err
 	}
 	results := make([]byte, 100)
 	count, err := ctl.Read(results)
 	if err != nil {
 		log.Printf("Failed to read from /port/%s/ctl: %#v\n", name, err)
-		return err
+		return nil, err
 	}
 	// We deliberately keep the control file open since 9P clunk
 	// will trigger a shutdown on the host side.
@@ -63,8 +67,8 @@ func exposePort(host net.Addr, port int) error {
 	if strings.HasPrefix(response, "ERROR ") {
 		os.Remove("/port/" + name + "/ctl")
 		response = strings.Trim(response[6:], " \t\r\n")
-		return errors.New(response)
+		return nil, errors.New(response)
 	}
-
-	return nil
+	// Hold on to a reference to prevent premature GC and close
+	return ctl, nil
 }