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 25io_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 30part 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> 39Do 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> 52The <strong>device_read_async</strong> interface enqueues a read operation for a 53sequence of bytes from a device object. The meaning of recnum as well 54as 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> 62Functions: 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>. 68