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<h2>device_read</h2>
<hr>
<p>
<strong>Function</strong> - Read a sequence of bytes from a specific device.
<h3>SYNOPSIS</h3>
<pre>
<strong>#include&ltdevice/device.h&gt</strong>

<strong>kern_return_t   device_read</strong>
                <strong>(device_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_ptr_t</strong>                      <var>io_buf_ptr_t</var>,
                 <strong>mach_msg_type_number_t</strong>  <var>mach_msg_type_number_t</var><strong>);</strong>


<strong>#include&ltdevice/device_request.h&gt</strong>

<strong>kern_return_t   device_read_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>);</strong>



<strong>kern_return_t   ds_device_read_reply</strong>
                <strong>(mach_port_t</strong>                         <var>reply_port</var>,
                 <strong>kern_return_t</strong>                      <var>return_code</var>,
                 <strong>io_buf_ptr_t</strong>                              <var>data</var>,
                 <strong>mach_msg_type_number_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>
[out pointer to dynamic array of bytes, in for asynchronous form]
Returned data bytes.
<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</strong> function reads a sequence of bytes
from a device object.  The
meaning of <var>recnum</var> as well as the specific operation performed is device
dependent.
<h3>RETURN VALUES</h3>
<p>
Only generic errors apply.
<h3>RELATED INFORMATION</h3>
<p>
Functions:
<a href="device_read_inband.html"><strong>device_read_inband</strong></a>,
<a href="device_read_overwrite.html"><strong>device_read_overwrite</strong></a>,
<a href="device_reply_server.html"><strong>device_reply_server</strong></a>.