title: How to use ffi.C.lstat?
body: <p>I want to get the file's basic infomation with the lstat function by  in my ngx_lua programme. The init.lua's content as fallow:</p>
  
  <pre><code>local ffi = require "ffi"
  local ffi_C = ffi.C
  local ffi_new = ffi.new
  
  ffi.cdef[[
      typedef long long time_t;
      typedef struct timespec {
          time_t  tv_sec;
          long    tv_nsec;
          ...;
      };
      typedef struct stat {
          struct timespec st_mtim;
          ...;
      };
  
      int lstat(const char *path, struct stat *buf);
  ]]
  
  buf = ffi_new("struct stat *")
  
  function checkfile (filename, buf)
      ffi_C.lstat(filename, buf)
  end
  </code></pre>
  
  <p>When I start my nginx, there are some errors happen. The content as fallow:</p>
  
  <ul>
  <li>2014/04/25 15:00:39 [error] 26396#0: lua entry thread aborted:
  runtime error: /home/nginx/conf/cop/init.lua:42:
  /usr/local/lib/libluajit-5.1.so.2: undefined symbol: lstat
     stack traceback:
     coroutine 0:
             [C]: in function '__index'
             /home/nginx/conf/cop/init.lua:42: in function 'checkfile'
             /home/nginx/conf/cop/check1.lua:37: in function , context: ngx.timer</li>
  </ul>