1*e13b1fa5SApple OSS Distributions<h2>device_read_async</h2> 2*e13b1fa5SApple OSS Distributions<hr> 3*e13b1fa5SApple OSS Distributions<p> 4*e13b1fa5SApple OSS Distributions<strong>System Trap</strong> - Read a sequence of bytes from a device object. 5*e13b1fa5SApple OSS Distributions<h3>SYNOPSIS</h3> 6*e13b1fa5SApple OSS Distributions<pre> 7*e13b1fa5SApple OSS Distributions<strong>kern_return_t device_read_async</strong> 8*e13b1fa5SApple OSS Distributions <strong>(mach_port_t</strong> <var>device</var>, 9*e13b1fa5SApple OSS Distributions <strong>mach_port_t</strong> <var>queue</var>, 10*e13b1fa5SApple OSS Distributions <strong>mach_port_t</strong> <var>request_id</var>, 11*e13b1fa5SApple OSS Distributions <strong>dev_mode_t</strong> <var>mode</var>, 12*e13b1fa5SApple OSS Distributions <strong>recnum_t</strong> <var>recnum</var>, 13*e13b1fa5SApple OSS Distributions <strong>io_buf_len_t</strong> <var>bytes_wanted</var><strong>);</strong> 14*e13b1fa5SApple OSS Distributions</pre> 15*e13b1fa5SApple OSS Distributions<h3>PARAMETERS</h3> 16*e13b1fa5SApple OSS Distributions<dl> 17*e13b1fa5SApple OSS Distributions<p> 18*e13b1fa5SApple OSS Distributions<dt> <var>device</var> 19*e13b1fa5SApple OSS Distributions<dd> 20*e13b1fa5SApple OSS Distributions[in device send right] A device port to the device to be read. 21*e13b1fa5SApple OSS Distributions<p> 22*e13b1fa5SApple OSS Distributions<dt> <var>queue</var> 23*e13b1fa5SApple OSS Distributions<dd> 24*e13b1fa5SApple OSS Distributions[in io_done queue send right] The port returned from 25*e13b1fa5SApple OSS Distributionsio_done_queue_create. 26*e13b1fa5SApple OSS Distributions<p> 27*e13b1fa5SApple OSS Distributions<dt> <var>request_id</var> 28*e13b1fa5SApple OSS Distributions<dd> 29*e13b1fa5SApple OSS Distributions[in send right] An unique request identifier that will be passed back as 30*e13b1fa5SApple OSS Distributionspart of the io_done_result structure. 31*e13b1fa5SApple OSS Distributions<p> 32*e13b1fa5SApple OSS Distributions<dt> <var>mode</var> 33*e13b1fa5SApple OSS Distributions<dd> 34*e13b1fa5SApple OSS Distributions[in scalar] I/O mode value. Meaningful options are: 35*e13b1fa5SApple OSS Distributions<p> 36*e13b1fa5SApple OSS Distributions <dl> 37*e13b1fa5SApple OSS Distributions<dt> <strong>D_NOWAIT</strong> 38*e13b1fa5SApple OSS Distributions<dd> 39*e13b1fa5SApple OSS DistributionsDo not wait if data is unavailable. 40*e13b1fa5SApple OSS Distributions </dl> 41*e13b1fa5SApple OSS Distributions<p> 42*e13b1fa5SApple OSS Distributions<dt> <var>recnum</var> 43*e13b1fa5SApple OSS Distributions<dd> 44*e13b1fa5SApple OSS Distributions[in scalar] Record number to be read. 45*e13b1fa5SApple OSS Distributions<p> 46*e13b1fa5SApple OSS Distributions<dt> <var>bytes_wanted</var> 47*e13b1fa5SApple OSS Distributions<dd> 48*e13b1fa5SApple OSS Distributions[in scalar] Size of data transfer. 49*e13b1fa5SApple OSS Distributions</dl> 50*e13b1fa5SApple OSS Distributions<h3>DESCRIPTION</h3> 51*e13b1fa5SApple OSS Distributions<p> 52*e13b1fa5SApple OSS DistributionsThe <strong>device_read_async</strong> interface enqueues a read operation for a 53*e13b1fa5SApple OSS Distributionssequence of bytes from a device object. The meaning of recnum as well 54*e13b1fa5SApple OSS Distributionsas the specific operation performed is device dependent. 55*e13b1fa5SApple OSS Distributions<h3>RETURN VALUES</h3> 56*e13b1fa5SApple OSS Distributions<dl> 57*e13b1fa5SApple OSS Distributions<strong>device_read_async</strong> returns only invalid parameter errors. 58*e13b1fa5SApple OSS Distributions<dd> 59*e13b1fa5SApple OSS Distributions</dl> 60*e13b1fa5SApple OSS Distributions<h3>RELATED INFORMATION</h3> 61*e13b1fa5SApple OSS Distributions<p> 62*e13b1fa5SApple OSS DistributionsFunctions: 63*e13b1fa5SApple OSS Distributions<a href="device_read_async_inband.html"><strong>device_read_async_inband</strong></a>, 64*e13b1fa5SApple OSS Distributions<a href="DR_overwrite_async.html"><strong>device_read_overwrite_async</strong></a>, 65*e13b1fa5SApple OSS Distributions<a href="device_write_async.html"><strong>device_write_async</strong></a>, 66*e13b1fa5SApple OSS Distributions<a href="device_write_async_inband.html"><strong>device_write_async_inband</strong></a>, 67*e13b1fa5SApple OSS Distributions<a href="io_done_queue_create.html"><strong>io_done_queue_create</strong></a>. 68