implement the dirstat extension in exportfs, greatly improving perf for OpenOS clients

lib/netutil.lua

@@ -16,6 +16,14 @@ end
 function netutil.exportfs(path) -- string -- boolean -- Export the directory *path* over RPC.
  local path = "/"..table.concat(fs.segments(path),"/")
  local px = require("unionfs").create(path)
+ function px.dirstat(p)
+  local rt = {}
+  for k,v in ipairs(px.list(p)) do
+   local fp = p.."/"..v
+   rt[v] = {px.isDirectory(fp), px.size(fp), px.lastModified(fp)}
+  end
+  return rt
+ end
  for k,v in pairs(px) do
   rpc.register("fs_"..path.."_"..k,v)
   print("fs_"..path.."_"..k)