(PECL eio >= 0.5.0b)
eio_seek — Repositions the offset of the open file associated with the fd argument to the argument offset according to the directive whence
$fd
   , int $offset
   , int $whence
   [, int $pri = EIO_PRI_DEFAULT
   [, callable $callback = NULL
   [, mixed $data = NULL
  ]]] )
    eio_seek() repositions the offset of the open file associated with 
   stream, Socket resource, or file descriptor specified by fd to the argument offset according to the directive whence as follows:
   
EIO_SEEK_SET - Set position equal to offset bytes.EIO_SEEK_CUR - Set position to current location plus offset.EIO_SEEK_END - Set position to end-of-file plus offset.fd
    Stream, Socket resource, or numeric file descriptor
offset
    Starting point from which data is to be read.
length
    Number of bytes to be read.
pri
    The 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]);
data
is custom data passed to the request.
result
request-specific result value; basically, the value returned by corresponding system call.
req
is optional request resource which can be used with functions like eio_get_last_error()
data
    
     Arbitrary variable passed to callback.
     
    eio_seek() returns request resource on success or FALSE on error.