Re: device_read example

[Neal H. Walfield]

At Sun, 18 Sep 2005 03:04:15 -0700 (PDT),
Shakthi Kannan wrote:
> I have a simple test function on GNU Hurd that
> 
> 1. gets_privileged_ports from device_t
>   
>   error_t err;
>   device_t device_master;
>   err = get_privileged_ports (0, &device_master);
> 
> 2. calls device_open
> 
>   err = device_open (device_master, D_READ | D_WRITE,
> "lpr", &lpr_dev);


My impression is that the fourth argument to device_open is a send
right to the device...

> 
> But, when I try to do device_read, it doesn't print
> message in the device_read function in
> gnumach-1-branch/i386/i386at/lpr.c
> 
> 3. calling device_read
> 
>   unsigned long result;
>   mach_msg_type_number_t data_cnt = sizeof (result); 
>   err = device_read (device_master, 0, -1, sizeof
> (result), (void *) &result, &data_cnt);

... which is supplied as the first argument to device_read et al.

The device master port is a meta-device which is used to obtain send
rights to other devices.


Also, make sure that you add your lprread function to the lpr device
structure (i.e. along side lpropen).