Subject: Re: [PATCH v6 28/32] config: read ref storage config on startup

From: David Turner <[email-masked]>
Date: Mon, 29 Feb 2016 16:57:42 -0500

On Fri, 2016-02-26 at 22:56 -0500, Jeff King wrote:
> On Wed, Feb 24, 2016 at 05:59:00PM -0500, David Turner wrote:
> 
> > @@ -1207,6 +1208,29 @@ int git_config_early(config_fn_t fn, void
> > *data, const char *repo_config)
> >  	}
> >  
> >  	if (repo_config && !access_or_die(repo_config, R_OK, 0)) {
> > +		char *storage = NULL;
> > +
> > +		/*
> > +		 * make sure we always read the ref storage config
> > +		 * from the extensions section on startup
> > +		 */
> > +		ret +=
> > git_config_from_file(ref_storage_backend_config,
> > +					    repo_config,
> > &storage);
> > +
> > +		register_ref_storage_backends();
> > +		if (!storage)
> > +			storage = xstrdup("");
> > +
> > +		if (!*storage ||
> > +		    !strcmp(storage, "files")) {
> > +			/* default backend, nothing to do */
> > +			free(storage);
> > +		} else {
> > +			if
> > (set_ref_storage_backend(ref_storage_backend))
> > +				die(_("Unknown ref storage backend
> > %s"),
> > +				    ref_storage_backend);
> > +		}
> > +
> 
> Coverity complains that "storage" leaks here, and I think it does in
> the
> case that we non-default storage, and we successfully set up the
> backend. That's a pretty minor point.
>
> However, after looking at this code, I'm rather confused about a few
> things.
> 
> One is that we read the config and use ref_storage_backend_config[1]
> to
> store the string value in "storage", and then we check whether that
> is
> non-default, and if it is, I'd expect us to feed it to
> set_ref_storage_backend. But we don't; we feed ref_storage_backend
> instead!
> 
> What is that value? It looks like it is the string we set in
> check_repo_format when we load the extensions list there. So why
> are we re-reading the config here at all? Couldn't we just use
> ref_storage_backend in the first place?
>
> My second confusion is why this is happening in git_config_early().
> That
> function is called during the setup of
> check_repository_format_gently(),
> which is why I think you wanted to put the code here. But it's _also_
> called as part of a regular git_config(). Which means we're parsing
> the
> repo config and setting the ref backend all over again, every time we
> look at config for other reasons.
> 
> So I think this setup probably should be in
> check_repository_format_gently(), and should be able to trigger off
> of
> the existing ref_storage_backend string we've already saved (and we
> should bail immediately there if we don't know about the backend, as
> it
> means we _don't_ match the repo's extensions and cannot proceed).

We apparently don't always call check_repo_format before calling
git_config_early -- or, more to the point, before doing ref operations.
So I think we need this in git_config_early.

I'll fix up the memory safety/leak issues tho.