(PECL eio >= 0.0.1dev)
eio_read — Read from a file descriptor at given offset.
$fd
   , int $length
   , int $offset
   , int $pri
   , callable $callback
   [, mixed $data = NULL
  ] )
   eio_read() reads up to length
   bytes from fd file descriptor at
   offset. The read bytes are stored in
   result argument of callback.
  
fdStream, Socket resource, or numeric file descriptor
lengthMaximum number of bytes to read.
offsetOffset within the file.
priThe request priority: EIO_PRI_DEFAULT, EIO_PRI_MIN, EIO_PRI_MAX, or NULL.
If NULL passed, pri internally is set to
EIO_PRI_DEFAULT.
callback
callback function is called when the request is done.
It should match the following prototype: 
void callback(mixed $data, int $result[, resource $req]);
datais custom data passed to the request.
resultrequest-specific result value; basically, the value returned by corresponding system call.
reqis optional request resource which can be used with functions like eio_get_last_error()
data
     Arbitrary variable passed to callback.
     
  eio_read() stores read bytes in
  result argument of callback
  function.
  
Example #1 eio_read() example
<?php
// Open a temporary file and write some bytes there
$temp_filename = "eio-temp-file.tmp";
$fp = fopen($temp_filename, "w");
fwrite($fp, "1234567890");
fclose($fp);
/* Is called when eio_read() is done */
function my_read_cb($data, $result) {
    global $temp_filename;
 // Output read bytes
    var_dump($result);
 // Close file
    eio_close($data);
    eio_event_loop();
 // Remove temporary file
    @unlink($temp_filename);
}
/* Is called when eio_open() is done */
function my_file_opened_callback($data, $result) {
 // $result should contain the file descriptor
    if ($result > 0) {
  // Read 5 bytes starting from third
        eio_read($result, 5, 2, EIO_PRI_DEFAULT, "my_read_cb", $result);
        eio_event_loop();
    } else {
  // eio_open() failed
        unlink($data);
    }
}
// Open the file for reading and writing
eio_open($temp_filename, EIO_O_RDWR, NULL,
    EIO_PRI_DEFAULT, "my_file_opened_callback", $temp_filename);
eio_event_loop();
?>
The above example will output something similar to:
string(5) "34567"