git mode 代码解释

create mode 100644到底是什么含义？
100代表regular file，644代表文件权限
参考/usr/share/doc/git-doc/technical/index-format.txt中的内容
  32-bit mode, split into (high to low bits)


    4-bit object type
      valid values in binary are 1000 (regular file), 1010 (symbolic link)
      and 1110 (gitlink)


    3-bit unused


    9-bit unix permission. Only 0755 and 0644 are valid for regular files.
    Symbolic links and gitlinks have value 0 in this field.
所以能够加入的文件类型就是100,101和111。