Hello Thomas, 

> Hi
> 
> I got a question in Resource manager usage
> 
> When we use devctl in the driver to send the data back to the user code ( 
> client) we use 
> 
> struct test* = _DEVCTL_DATA(msg->o);
> 
> // Code to populate the test structure 
> 
>   if (nbytes == 0) {
>         return (_RESMGR_ERRNO (EOK));
>     } else {
>         msg -> o.ret_val = 0;
>         msg -> o.nbytes = nbytes;
>         return (_RESMGR_PTR (ctp, &msg -> o, sizeof (msg -> o) + nbytes));
> 
> }
> 
> with the above code we expect the struct test content will be there in the 
> caller function (client)
> 
> Q1. Do we need to do memset().. memset(&msg->o, 0, sizeof(msg->o)); 
No. Well, to be defensive, simply  add "msg -> o.zero = msg->o.zero2 = 0"
> If yes why  it is needed. ? As i am not understanding where the test data will be stored 
> ?
In your code  you simply use the input buffer (msg->i) as output buffer (msg->o) for the message reply.

 
> 
> Q2. I am facing a problem where the data is not transfered to the client. How 
> to check.? 

The devctl cmds. which received data, need the ..._FROM Flag in their definition, otherwise your buffer will not receive
 your test struct. 
If your test struct is of variable length, you can use the o.ret_val member to return the length.

> 
> Q3. When we are passing structure from the Resource manager to the client do 
> we need to use _DEVCTL_DATA(msg->o) or
> _DEVCTL_DATA(msg->i)
> 

You should use msg->o, but in your case it doesn't matter. devctl IN and OUT message header have the same size.

-Michael