+<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>.