threads / discuss / 61832

EXDEV when re-init with --separate-git-dir option

Subject: EXDEV when re-init with --separate-git-dir option

## tl;dr

3 messages between Jul 24, 2024 and Jul 24, 2024.

replies: 2people: 3as markdown or json

Jin, Di· Jul 24, 2024, 02:47 UTC · lore

Dear maintainers,

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.

An example is shown below:

$ mkdir -p fs1/gitdir fs2 $ ls fs1 fs2 $ sudo mount -t tmpfs tmpfs fs2 $ cd fs1/gitdir $ git init Initialized empty Git repository in /home/user/fs1/gitdir/.git/ $ git init --separate-git-dir ../../fs2/surrealgitdir fatal: unable to move /home/user/fs1/gitdir/.git to /home/user/fs2/surrealgitdir: Invalid cross-device link

We tested this on version v2.45.2 and after reading the code a bit we believe the issue still exist in the master branch on github (https://github.com/git/git/blob/d19b6cd2dd72dc811f19df4b32c7ed223256c3ee/setup.c#L2280).

Best regards, Di

Junio C Hamano· Jul 24, 2024, 15:39 UTC · re: Jin, Di · lore

Re: EXDEV when re-init with --separate-git-dir option

"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.

Eric Sunshine· Jul 24, 2024, 17:14 UTC · re: Junio C Hamano · lore

Re: EXDEV when re-init with --separate-git-dir option

On Wed, Jul 24, 2024 at 11:40 AM Junio C Hamano <gitster@pobox.com> wrote:

Show 13 quoted lines

> "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.
> [...]
> 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.

Re-init with --separate-git-dir isn't the only problem spot. `git worktree move` also suffers the same problem for the same reason.

> 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.

This wouldn't help Windows users.

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

It might be a bit more than bite-sized, though, considering the above points about `git worktree move` also needing such a fix, and having to deal with Microsoft Windows.