sandbox: support vsock connection to task api

Signed-off-by: Abel Feng <fshb1988@gmail.com>

vendor/github.com/mdlayher/vsock/fd_linux.go

@@ -0,0 +1,36 @@
+package vsock
+
+import (
+	"fmt"
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+// contextID retrieves the local context ID for this system.
+func contextID() (uint32, error) {
+	f, err := os.Open(devVsock)
+	if err != nil {
+		return 0, err
+	}
+	defer f.Close()
+
+	return unix.IoctlGetUint32(int(f.Fd()), unix.IOCTL_VM_SOCKETS_GET_LOCAL_CID)
+}
+
+// isErrno determines if an error a matches UNIX error number.
+func isErrno(err error, errno int) bool {
+	switch errno {
+	case ebadf:
+		return err == unix.EBADF
+	case enotconn:
+		return err == unix.ENOTCONN
+	default:
+		panicf("vsock: isErrno called with unhandled error number parameter: %d", errno)
+		return false
+	}
+}
+
+func panicf(format string, a ...interface{}) {
+	panic(fmt.Sprintf(format, a...))
+}