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<h2>device_read_overwrite</h2>
<hr>
<p><strong>System Trap</strong> -- Read a sequence of bytes from a specific device into my address space.
<h3>SYNOPSIS</h3>
<pre>

<strong>kern_return_t   device_read_overwrite</strong>
                <strong>(mach_port_t</strong>                               <var>device</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_pointer_t</strong>                          <var>data</var>,
                 <strong>mach_msg_type_number_t</strong>              <var>data_count</var><strong>);</strong>



<strong>kern_return_t   device_read_overwrite_request</strong>
                <strong>(mach_port_t</strong>                             <var>device</var>,
                 <strong>mach_port_t</strong>                         <var>reply_port</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_pointer_t</strong>                          <var>data</var><strong>);</strong>



<strong>kern_return_t   ds_device_read_reply_overwrite</strong>
                <strong>(mach_port_t</strong>                        <var>reply_port</var>,
                 <strong>kern_return_t</strong>                      <var>return_code</var>,
                 <strong>io_buf_len_t</strong>                        <var>data_count</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>reply_port</var> 
<dd>
[in reply receive (to be converted to send-once) right]
The port to 
which the reply message is to be sent.
<p>
<dt> <var>mode</var> 
<dd>
[in scalar]
I/O mode value.  Meaningful options are:
<dl>
<p>
<dt> <strong>D_NOWAIT</strong>
<dd>
Do not wait if data is unavailable.
</dl>
<p>
<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>return_code</var> 
<dd>
[in scalar]
The return status code from the read.
<p>
<dt> <var>data</var> 
<dd>
[pointer to in array of bytes]
Data buffer to be overwritten.
<p>
<dt> <var>data_count</var> 
<dd>
[out scalar, in for asynchronous form]
Number of returned data bytes.
</dl>
<h3>DESCRIPTION</h3>
<p>
The <strong>device_read_overwrite</strong> system trap reads a sequence
of bytes from a
device object directly into the caller's address space.  The
meaning of <var>recnum</var> as 
well as the specific operation performed is device dependent.
<h3>NOTES</h3>
<p>
The <strong>device_read_overwrite_request</strong> and <strong>device_read_reply_overwrite</strong>
calls may be removed from the interface in favor of new asynchronous support.
<h3>RETURN VALUES</h3>
<p>
Only generic errors apply.
<h3>RELATED INFORMATION</h3>
<p>
Functions:
<a href="device_read.html"><strong>device_read</strong></a>,
<a href="device_read_inband.html"><strong>device_read_inband</strong></a>,
<a href="device_reply_server.html"><strong>device_reply_server</strong></a>.