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From: Junio C Hamano <gitster@pobox.com>
To: "Jin, Di" <di_jin@brown.edu>
Cc: git@vger.kernel.org,  Nikos Vasilakis <nikos_vasilakis@brown.edu>,
  michael@greenberg.science
Subject: Re: EXDEV when re-init with --separate-git-dir option
In-Reply-To: <CAKOkDnMGRfQoNygYLiAxPZB2q=VMYvw8kyu1dM=pM843-FH41Q@mail.gmail.com>
	(Di Jin's message of "Tue, 23 Jul 2024 22:47:19 -0400")
References: <CAKOkDnMGRfQoNygYLiAxPZB2q=VMYvw8kyu1dM=pM843-FH41Q@mail.gmail.com>
Date: Wed, 24 Jul 2024 08:39:49 -0700
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"Jin, Di" <di_jin@brown.edu> writes:

> We discovered that re-init with option --separate-git-dir will throw
> an EXDEV when the target directory is not on the same file system as
> the original directory.

Yup, it is hitting the limitation of your filesystem.  The code
wants to move the original .git directory together with its contents
to a new place, and it makes a single rename() system call to do so.
When the system cannot do so, you'd get the error message you are
seeing ("fatal: unable to move X to Y").

The code path could probably borrow some code to recursively "copy"
directory from the local "git clone" code path, and then invent a
new code to recursively remove the original ".git", and trigger that
new code when rename() fails.

But at that point, only as a fall-back measure, it might be simpler
and much less error prone to spawn a "mv src dst" as a subprocess
using the run_command() API.

It would make a good bite-sized #leftoverbits project for aspiring
new Git contributors.  Any takers?  ;-)

Thanks.