git submodule update needs to be at the toplevel of working tree, why?

Hi,

I'm usually in a subfolder doing actual work. A very common problem I have is wanting to do a submodule update, but git really hates that. And I wonder why?

It wouldn't be hard to cd to the toplevel working directory, do the update, and cd back. It's what I have to do manually every time now already:

  $ git submodule update
  You need to run this command from the toplevel of the working tree.

  $ cd ../..

  $ git submodule update
  Submodule path 'myproject/libs/external-module': checked out
  '434fdf32a7add62...

  $ cd -

I see that it comes from git-sh-setup, so no rationale for this rather weird and surprising behavior is given in the git-submodule file. :)