osfmk/man/device_read_async.html

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