code: function (ds, acc, m, cb) {
      if (ds.length > 0) {
        var d = ds.shift();
  
        acc.push(d);
        var dir = acc.join(path.sep);
  
        // look for dir on the fs, if it doesn't exist then create it, and 
        // continue our walk, otherwise if it's a file, we have a name
        // collision, so exit.
        fs.stat(dir, function (err, stat) {
          // if the directory doesn't exist then create it
          if (err) {
            // 2 means it's wasn't there
            if (err.errno == 2 || err.errno == 34) {
              fs.mkdir(dir, m, function (erro) {
                if (erro && erro.errno != 17 && erro.errno != 34) {
                  return cb(erro);
                } else {
                  return walk(ds, acc, m, cb);
                }
              });
            } else {
              return cb(err);
            }
          } else {
            if (stat.isDirectory()) {
              return walk(ds, acc, m, cb);
            } else {
              return cb(new Error("Failed to mkdir " + dir + ": File exists\n"));
            }
          }
        });
      } else {
        return cb();
      }
    }
docs: walk @ds:  A list of directory names @acc: An accumulator of walked dirs @m:   The mode @cb:  The callback