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<h2>device_read_overwrite_async</h2>
<hr>
<p>
<strong>System Trap</strong> - Read a sequence of bytes from a device object into the caller's 
<h3>SYNOPSIS</h3>
<pre>
<strong>kern_return_t   device_read_overwrite_async</strong>
                <strong>(mach_port_t</strong>                             <var>device</var>,
                 <strong>mach_port_t</strong>                              <var>queue</var>,
                 <strong>mach_port_t</strong>                         <var>request_id</var>,
                 <strong>dev_mode_t</strong>                                <var>mode</var>,
                 <strong>recnum_t</strong>                                <var>recnum</var>,
                 <strong>io_buf_len_t</strong>                      <var>bytes_wanted</var>,
                 <strong>io_buf_ptr_t</strong>                            <var>buffer</var><strong>);</strong>
</pre>
<h3>PARAMETERS</h3>
<dl>
<p>
<dt> <var>device</var>
<dd>
[in device send right] A device port to the device to be read.
<p>
<dt> <var>queue</var>
<dd>
[in io_done queue send right] The port returned from the 
io_done_queue_create call.
<p>
<dt> <var>request_id</var>
<dd>
[in send right] An unique request identifier that will be passed back as 
part of the io_done_result structure.
<p>
<dt> <var>mode</var>
<dd>
[in scalar] I/O mode value. Meaningful options are:
<p>
     <dl>
<dt> <strong>D_NOWAIT</strong>
<dd>
Do not wait if data is unavailable.
<p>
     </dl>
<dt> <var>recnum</var>
<dd>
[in scalar] Record number to be read.
<p>
<dt> <var>bytes_wanted</var>
<dd>
[in scalar] Size of data transfer.
<p>
<dt> <var>buffer</var>
<dd>
[pointer to in array of bytes] Data buffer to be overwritten.
</dl>
<h3>DESCRIPTION</h3>
<p>
The <strong>device_read_overwrite</strong> system trap enqueues a read operation for a
sequence of bytes from a device object to be placed directly into
the caller's address space. The meaning of recnum as well as the
specific operation performed is device dependent.
<h3>RETURN VALUES</h3>
<p>
<strong>device_read_overwrite_async</strong> returns only invalid parameter errors.
<h3>RELATED INFORMATION</h3>
<p>
Functions:
<a href="device_read_async.html"><strong>device_read_async</strong></a>,
<a href="device_read_async_inband.html"><strong>device_read_async_inband</strong></a>,
<a href="device_write_async.html"><strong>device_write_async</strong></a>,
<a href="device_write_async_inband.html"><strong>device_write_async_inband</strong></a>,
<a href="io_done_queue_create.html"><strong>io_done_queue_create</strong></a>.