1<h2>device_read_overwrite_async</h2> 2<hr> 3<p> 4<strong>System Trap</strong> - Read a sequence of bytes from a device object into the caller's 5<h3>SYNOPSIS</h3> 6<pre> 7<strong>kern_return_t device_read_overwrite_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>, 14 <strong>io_buf_ptr_t</strong> <var>buffer</var><strong>);</strong> 15</pre> 16<h3>PARAMETERS</h3> 17<dl> 18<p> 19<dt> <var>device</var> 20<dd> 21[in device send right] A device port to the device to be read. 22<p> 23<dt> <var>queue</var> 24<dd> 25[in io_done queue send right] The port returned from the 26io_done_queue_create call. 27<p> 28<dt> <var>request_id</var> 29<dd> 30[in send right] An unique request identifier that will be passed back as 31part of the io_done_result structure. 32<p> 33<dt> <var>mode</var> 34<dd> 35[in scalar] I/O mode value. Meaningful options are: 36<p> 37 <dl> 38<dt> <strong>D_NOWAIT</strong> 39<dd> 40Do not wait if data is unavailable. 41<p> 42 </dl> 43<dt> <var>recnum</var> 44<dd> 45[in scalar] Record number to be read. 46<p> 47<dt> <var>bytes_wanted</var> 48<dd> 49[in scalar] Size of data transfer. 50<p> 51<dt> <var>buffer</var> 52<dd> 53[pointer to in array of bytes] Data buffer to be overwritten. 54</dl> 55<h3>DESCRIPTION</h3> 56<p> 57The <strong>device_read_overwrite</strong> system trap enqueues a read operation for a 58sequence of bytes from a device object to be placed directly into 59the caller's address space. The meaning of recnum as well as the 60specific operation performed is device dependent. 61<h3>RETURN VALUES</h3> 62<p> 63<strong>device_read_overwrite_async</strong> returns only invalid parameter errors. 64<h3>RELATED INFORMATION</h3> 65<p> 66Functions: 67<a href="device_read_async.html"><strong>device_read_async</strong></a>, 68<a href="device_read_async_inband.html"><strong>device_read_async_inband</strong></a>, 69<a href="device_write_async.html"><strong>device_write_async</strong></a>, 70<a href="device_write_async_inband.html"><strong>device_write_async_inband</strong></a>, 71<a href="io_done_queue_create.html"><strong>io_done_queue_create</strong></a>. 72