Re: [PATCH/RFC] Revoke write access to refs and odb after importing another repo's odb

From: Junio C Hamano <gitster@pobox.com>
Date: Jan 23, 2013, 17:01 UTC
Message-ID: <7v1udbj0kt.fsf@alter.siamese.dyndns.org>
In-Reply-To: <1358948067-2792-1-git-send-email-pclouds@gmail.com>

Nguyễn Thái Ngọc Duy  <pclouds@gmail.com> writes:

Show 18 quoted lines

> add_submodule_odb() can be used to import objects from another
> repository temporarily. After this point we don't know which objects
> are ours, which are external. If we create an object that refers to an
> external object, next time git runs, it may find a hole in the object
> graph because the external repository may not be imported. The same
> goes for pointing a ref to an external SHA-1.
>
> To protect ourselves, once add_submodule_odb() is used:
>
>  - trees, tags and commits cannot be created
>  - refs cannot be updated
>
> In certain cases that submodule code knows that it's safe to write, it
> can turn the readonly flag off.
>
> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
> ---
>  I think this is a good safety check.

Two step implementation to bring "read-only" support into a testable shape and then flip that bit in add_submdule_odb() would be a sensible approach.

I however have this suspicion that this will become a losing battle and we would be better off getting rid of add_submodule_odb(); instead operations that work across repositories will be done as a subprocess, which will get us back closer to one of the original design goals of submodule support to have a clear separation between the superproject and its submodules.