1<h2>device_read_overwrite_async</h2>
2<hr>
3<p>
4<strong>System Trap</strong> - Read a sequence of bytes from a device object into the caller's 
5<h3>SYNOPSIS</h3>
6<pre>
7<strong>kern_return_t   device_read_overwrite_async</strong>
8                <strong>(mach_port_t</strong>                             <var>device</var>,
9                 <strong>mach_port_t</strong>                              <var>queue</var>,
10                 <strong>mach_port_t</strong>                         <var>request_id</var>,
11                 <strong>dev_mode_t</strong>                                <var>mode</var>,
12                 <strong>recnum_t</strong>                                <var>recnum</var>,
13                 <strong>io_buf_len_t</strong>                      <var>bytes_wanted</var>,
14                 <strong>io_buf_ptr_t</strong>                            <var>buffer</var><strong>);</strong>
15</pre>
16<h3>PARAMETERS</h3>
17<dl>
18<p>
19<dt> <var>device</var>
20<dd>
21[in device send right] A device port to the device to be read.
22<p>
23<dt> <var>queue</var>
24<dd>
25[in io_done queue send right] The port returned from the 
26io_done_queue_create call.
27<p>
28<dt> <var>request_id</var>
29<dd>
30[in send right] An unique request identifier that will be passed back as 
31part of the io_done_result structure.
32<p>
33<dt> <var>mode</var>
34<dd>
35[in scalar] I/O mode value. Meaningful options are:
36<p>
37     <dl>
38<dt> <strong>D_NOWAIT</strong>
39<dd>
40Do not wait if data is unavailable.
41<p>
42     </dl>
43<dt> <var>recnum</var>
44<dd>
45[in scalar] Record number to be read.
46<p>
47<dt> <var>bytes_wanted</var>
48<dd>
49[in scalar] Size of data transfer.
50<p>
51<dt> <var>buffer</var>
52<dd>
53[pointer to in array of bytes] Data buffer to be overwritten.
54</dl>
55<h3>DESCRIPTION</h3>
56<p>
57The <strong>device_read_overwrite</strong> system trap enqueues a read operation for a
58sequence of bytes from a device object to be placed directly into
59the caller's address space. The meaning of recnum as well as the
60specific operation performed is device dependent.
61<h3>RETURN VALUES</h3>
62<p>
63<strong>device_read_overwrite_async</strong> returns only invalid parameter errors.
64<h3>RELATED INFORMATION</h3>
65<p>
66Functions:
67<a href="device_read_async.html"><strong>device_read_async</strong></a>,
68<a href="device_read_async_inband.html"><strong>device_read_async_inband</strong></a>,
69<a href="device_write_async.html"><strong>device_write_async</strong></a>,
70<a href="device_write_async_inband.html"><strong>device_write_async_inband</strong></a>,
71<a href="io_done_queue_create.html"><strong>io_done_queue_create</strong></a>.
72