On Sun, Oct 01, 2023 at 09:40:08PM -0500, Eric W. Biederman wrote:
> From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
>
> We currently have support for using a full stage 4 SHA-256
> implementation.
What is a "full stage 4 SHA-256 implementation"? I was assuming that you
referred to "Documentation/technical/hash-function-transition.txt", but
it does not mention stages either.
> However, we'd like to support interoperability with
> SHA-1 repositories as well. The transition plan anticipates a
> compatibility hash algorithm configuration option that we can use to
> implement support for this. Let's add an element to the repository
> structure that indicates the compatibility hash algorithm so we can use
> it when we need to consider interoperability between algorithms.
>
> Add a helper function repo_set_compat_hash_algo that takes a
> compatibility hash algorithm and sets "repo->compat_hash_algo". If
> GIT_HASH_UNKNOWN is passed as the compatibility hash algorithm
> "repo->compat_hash_algo" is set to NULL.
>
> For now, the code results in "repo->compat_hash_algo" always being set
> to NULL, but that will change once a configuration option is added.
>
> Inspired-by: brian m. carlson <sandals@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> ---
> repository.c | 8 ++++++++
> repository.h | 4 ++++
> setup.c | 3 +++
> 3 files changed, 15 insertions(+)
>
> diff --git a/repository.c b/repository.c
> index a7679ceeaa45..80252b79e93e 100644
> --- a/repository.c
> +++ b/repository.c
> @@ -104,6 +104,13 @@ void repo_set_hash_algo(struct repository *repo, int hash_algo)
> repo->hash_algo = &hash_algos[hash_algo];
> }
>
> +void repo_set_compat_hash_algo(struct repository *repo, int algo)
> +{
> + if (hash_algo_by_ptr(repo->hash_algo) == algo)
> + BUG("hash_algo and compat_hash_algo match");
> + repo->compat_hash_algo = algo ? &hash_algos[algo] : NULL;
> +}
> +
> /*
> * Attempt to resolve and set the provided 'gitdir' for repository 'repo'.
> * Return 0 upon success and a non-zero value upon failure.
> @@ -184,6 +191,7 @@ int repo_init(struct repository *repo,
> goto error;
>
> repo_set_hash_algo(repo, format.hash_algo);
> + repo_set_compat_hash_algo(repo, GIT_HASH_UNKNOWN);
> repo->repository_format_worktree_config = format.worktree_config;
>
> /* take ownership of format.partial_clone */
> diff --git a/repository.h b/repository.h
> index 5f18486f6465..bf3fc601cc53 100644
> --- a/repository.h
> +++ b/repository.h
> @@ -160,6 +160,9 @@ struct repository {
> /* Repository's current hash algorithm, as serialized on disk. */
> const struct git_hash_algo *hash_algo;
>
> + /* Repository's compatibility hash algorithm. */
> + const struct git_hash_algo *compat_hash_algo;
> +
> /* A unique-id for tracing purposes. */
> int trace2_repo_id;
>
> @@ -199,6 +202,7 @@ void repo_set_gitdir(struct repository *repo, const char *root,
> const struct set_gitdir_args *extra_args);
> void repo_set_worktree(struct repository *repo, const char *path);
> void repo_set_hash_algo(struct repository *repo, int algo);
> +void repo_set_compat_hash_algo(struct repository *repo, int compat_algo);
> void initialize_the_repository(void);
> RESULT_MUST_BE_USED
> int repo_init(struct repository *r, const char *gitdir, const char *worktree);
> diff --git a/setup.c b/setup.c
> index 18927a847b86..aa8bf5da5226 100644
> --- a/setup.c
> +++ b/setup.c
> @@ -1564,6 +1564,8 @@ const char *setup_git_directory_gently(int *nongit_ok)
> }
> if (startup_info->have_repository) {
> repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
> + repo_set_compat_hash_algo(the_repository,
> + GIT_HASH_UNKNOWN);
> the_repository->repository_format_worktree_config =
> repo_fmt.worktree_config;
> /* take ownership of repo_fmt.partial_clone */
> @@ -1657,6 +1659,7 @@ void check_repository_format(struct repository_format *fmt)
> check_repository_format_gently(get_git_dir(), fmt, NULL);
> startup_info->have_repository = 1;
> repo_set_hash_algo(the_repository, fmt->hash_algo);
> + repo_set_compat_hash_algo(the_repository, GIT_HASH_UNKNOWN);
> the_repository->repository_format_worktree_config =
> fmt->worktree_config;
> the_repository->repository_format_partial_clone =
There's also `init_db()`, where we call `repo_set_hash_algo()`. Would we
have to call `repo_set_compat_hash_algo()` there, too? There are some
other locations when handling remotes or clones, but I don't think those
are relevant right now.
Patrick
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