Re: [PATCH v6 3/5] config: learn `git_protected_config()`

[Taylor Blau <me@ttaylorr.com>]

On Thu, Jun 30, 2022 at 06:13:57PM +0000, Glen Choo via GitGitGadget wrote:
> In light of constraint 1, this implementation can still be improved
> since git_protected_config() iterates through every variable in
> protected_config, which may still be too expensive. There exist constant
> time lookup functions for non-protected configuration
> (repo_config_get_*()), but for simplicity, this commit does not
> implement similar functions for protected configuration.

I don't quite follow along with this paragraph: it sounds like reading
protected configuration is supposed to be as fast as possible. But you
note that only the slower variant of reading each configuration variable
one at a time is implemented.

If we care about speed (and I think we should here), then would it make
more sense to implement only the lookup functions like
repo_config_get_*() for protected context? That would encourage usage by
providing a more limited set of options to callers.

> Signed-off-by: Glen Choo <chooglen@google.com>
> ---
>  config.c                     | 51 ++++++++++++++++++++++++++++++++++++
>  config.h                     | 17 ++++++++++++
>  t/t5544-pack-objects-hook.sh |  7 ++++-
>  upload-pack.c                | 27 ++++++++++++-------
>  4 files changed, 91 insertions(+), 11 deletions(-)
>
> diff --git a/config.c b/config.c
> index 9b0e9c93285..29e62f5d0ed 100644
> --- a/config.c
> +++ b/config.c
> @@ -81,6 +81,18 @@ static enum config_scope current_parsing_scope;
>  static int pack_compression_seen;
>  static int zlib_compression_seen;
>
> +/*
> + * Config that comes from trusted sources, namely:

Should we be using the word "scope" here instead of sources? I think
it's clear enough from the context what you're referring to, but in the
spirit of being consistent...

> + * - system config files (e.g. /etc/gitconfig)
> + * - global config files (e.g. $HOME/.gitconfig,
> + *   $XDG_CONFIG_HOME/git)
> + * - the command line.
> + *
> + * This is declared here for code cleanliness, but unlike the other
> + * static variables, this does not hold config parser state.
> + */
> +static struct config_set protected_config;
> +
>  static int config_file_fgetc(struct config_source *conf)
>  {
>  	return getc_unlocked(conf->u.file);
> @@ -2378,6 +2390,11 @@ int git_configset_add_file(struct config_set *cs, const char *filename)
>  	return git_config_from_file(config_set_callback, filename, cs);
>  }
>
> +int git_configset_add_parameters(struct config_set *cs)
> +{
> +	return git_config_from_parameters(config_set_callback, cs);
> +}
> +
>  int git_configset_get_value(struct config_set *cs, const char *key, const char **value)
>  {
>  	const struct string_list *values = NULL;
> @@ -2619,6 +2636,40 @@ int repo_config_get_pathname(struct repository *repo,
>  	return ret;
>  }
>
> +/* Read values into protected_config. */
> +static void read_protected_config(void)
> +{
> +	char *xdg_config = NULL, *user_config = NULL, *system_config = NULL;
> +
> +	git_configset_init(&protected_config);
> +
> +	system_config = git_system_config();
> +	git_global_config(&user_config, &xdg_config);
> +
> +	git_configset_add_file(&protected_config, system_config);
> +	git_configset_add_file(&protected_config, xdg_config);
> +	git_configset_add_file(&protected_config, user_config);
> +	git_configset_add_parameters(&protected_config);
> +
> +	free(system_config);
> +	free(xdg_config);
> +	free(user_config);
> +}
> +
> +/* Ensure that protected_config has been initialized. */
> +static void git_protected_config_check_init(void)
> +{
> +	if (protected_config.hash_initialized)
> +		return;
> +	read_protected_config();
> +}
> +
> +void git_protected_config(config_fn_t fn, void *data)
> +{
> +	git_protected_config_check_init();

This may be copying from an existing pattern, but I think you could
avoid the extra function declaration by writing git_protected_config()
as:

    if (!protected_config.hash_initialized)
        read_protected_config();
    configset_iter(&protected_config, fn, data);

Thanks,
Taylor