Description:
------------
Php doesn't get any input from a serialport, after opening the devicefile and writing to it. Maybe this is thought to be so - and maybe it is a feature. For those cases: sorry for stealing ur time. 


Infact, there IS a response from the device. The difference between "strace php -f example.php" and "strace cat /dev/ttyUSB0" (nonblocking-mode in php):

php wont get the input. for php, the device is "temporarily unavailable":
"read(3, 0x17e4a4, 1024)                 = -1 EAGAIN (Resource temporarily unavailable)"

cat gets the answer from the device:
"read(3, "\0\340", 4096)                 = 2"


There is no difference, if i use fopen, or dio_open: php wont get the answer from my device.
There is also no difference, if i use fread, fgets or dio_read. 

The lib i used can be seen here: http://nopaste.php-q.net/176167


Tested on a x86 and an embedded-arm machine, both running an actual linux >2.6.12-r1 kernel. The chmods for the devices were set correctly. 

Reproduce code:
---------------
<?php
$fp = fopen('/dev/ttyUSB0','r+');
#fp = fopen('/dev/ttyUSB0','w+');
fputs($fp,chr(0xff),1);
$buffer = fread($fp,1);
fclose($fp);
?>

<?php
$fp = dio_open('/dev/ttyUSB0', O_RDWR | O_NOCTTY | O_NONBLOCK | O_APPEND);
dio_write($fp,chr(0xff));
$buffer = dio_read($fp,1);
dio_close($fp);
?>


Expected result:
----------------
I expected to get the answer in $buffer by fread, fgets or dio_read. But the answer from the device (wich i can see in cat /dev/ttyUSB0) didnt came up in php. 

Actual result:
--------------
The strace of "cat /dev/ttyUSB0", you can see here:
<snip>
read(3, "\0\340", 4096)                 = 2
</snip>

Should appear also at "strace php -f example.php". but it doesnt. When the devicefile is opened in nonblocking mode, the relevant strace-output is:
<snip>
read(3, 0x17e4a4, 1024)                 = -1 EAGAIN (Resource temporarily unavailable)
</snip>

When the devicefile is opened in blockingmode, it just hangs at
<snip>
read(3,
</snip>