Re: [PATCH] fsck: detect bare repos in trees and warn

[Glen Choo <chooglen@google.com>]

Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:

> On Thu, Apr 07 2022, Derrick Stolee wrote:
>
>> A more complete protection here would be:
>>
>>  1. Warn when finding a bare repo as a tree (this patch).
>>
>>  2. Suppress warnings on trusted repos, scoped to a specific set of known
>>     trees _or_ based on some set of known commits (in case the known trees
>>     are too large).
>>
>>  3. Prevent writing a bare repo to the worktree, unless the user provided
>>     an opt-in to that behavior.
>>
>> Since your patch is moving in the right direction here, I don't think
>> steps (2) and (3) are required to move forward with your patch. However,
>> it is a good opportunity to discuss the full repercussions of this issue.
>
> Isn't a gentler solution here to:
>
>  1. In setup.c, we detect a repo
>  2. Walk up a directory
>  3. Do we find a repo?
>  4. Does that repo "contain" the first one?
>     If yes: die on setup
>     If no: it's OK
>
> It also seems to me that there's pretty much perfect overlap between
> this and the long-discussed topic of marking a submodule with config
> v.s. detecting it on the fly.

Your suggestion seems similar to:

  == 3. Detect that we are in an embedded bare repo and ignore the embedded bare
  repository in favor of the containing repo.

which I also think is a simple, robust mitigation if we put aside the
problem of walking up to the root in too many situations. I seem to
recall that this problem has come up before in [1] (and possibly other
topics? I wasn't really able to locate them through a cursory search..),
so I assume that's what you're referring to by "long-discussed topic".

(Forgive me if I'm asking you to repeat yourself yet another time) I
seem to recall that we weren't able to reach consensus on whether it's
okay for Git to opportunistically walk up the directory hierarchy during
setup, especially since There are some situations where this is
extremely expensive (VFS, network mount).

I actually like this option quite a lot, but I don't see how we could
implement this without imposing a big penalty to all bare repo users -
they'd either be forced to set GIT_DIR or GIT_CEILING_DIRECTORIES, or
take a (potentially big) performance hit. Hopefully I'm just framing
this too narrowly and you're approaching this differently.

PS: As an aside, wouldn't this also break libgit2? We could make this
opt-out behavior, though that requires us to read system config _before_
discovering the gitdir (as I discussed in [2]).

[1] https://lore.kernel.org/git/211109.86v912dtfw.gmgdl@evledraar.gmail.com/
[2] https://lore.kernel.org/git/kl6lv8vc90ts.fsf@chooglen-macbookpro.roam.corp.google.com