Re: [PATCH v6 18/27] files-backend: replace submodule_allowed check in files_downcast()

> files-backend.c is unlearning submodules. Instead of having a specific
> check for submodules to see what operation is allowed, files backend
> now takes a set of flags at init. Each operation will check if the
> required flags is present before performing.
> 
> For now we have four flags: read, write and odb access. Main ref store
> has all flags, obviously, while submodule stores are read-only and have
> access to odb (*).
> 
> The "main" flag stays because many functions in the backend calls
> frontend ones without a ref store, so these functions always target the
> main ref store. Ideally the flag should be gone after ref-store-aware
> api is in place and used by backends.
> 
> (*) Submodule code needs for_each_ref. Try take REF_STORE_ODB flag
> out. At least t3404 would fail. The "have access to odb" in submodule is
> a bit hacky since we don't know from he whether add_submodule_odb() has
> been called.
> 
> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
> ---
>  refs.c               | 15 ++++++---
>  refs/files-backend.c | 86 +++++++++++++++++++++++++++++++++-------------------
>  refs/refs-internal.h |  9 +++++-
>  3 files changed, 73 insertions(+), 37 deletions(-)
> 
> [...]
> diff --git a/refs/files-backend.c b/refs/files-backend.c
> index db335e4ca6..7d8d4dcc16 100644
> --- a/refs/files-backend.c
> +++ b/refs/files-backend.c
> [...]
> @@ -1923,21 +1935,23 @@ static struct ref_iterator *files_ref_iterator_begin(
>  		struct ref_store *ref_store,
>  		const char *prefix, unsigned int flags)
>  {
> -	struct files_ref_store *refs =
> -		files_downcast(ref_store, 1, "ref_iterator_begin");
> +	struct files_ref_store *refs;
>  	struct ref_dir *loose_dir, *packed_dir;
>  	struct ref_iterator *loose_iter, *packed_iter;
>  	struct files_ref_iterator *iter;
>  	struct ref_iterator *ref_iterator;
>  
> -	if (!refs)
> -		return empty_ref_iterator_begin();
> -
>  	if (ref_paranoia < 0)
>  		ref_paranoia = git_env_bool("GIT_REF_PARANOIA", 0);
>  	if (ref_paranoia)
>  		flags |= DO_FOR_EACH_INCLUDE_BROKEN;
>  
> +	refs = files_downcast(ref_store,
> +			      REF_STORE_READ | (ref_paranoia ? 0 : REF_STORE_ODB),
> +			      "ref_iterator_begin");
> +	if (!refs)
> +		return empty_ref_iterator_begin();
> +

> [...]
> diff --git a/refs/refs-internal.h b/refs/refs-internal.h
> index dfa1817929..0cca280b5c 100644
> --- a/refs/refs-internal.h
> +++ b/refs/refs-internal.h
> @@ -481,12 +481,19 @@ struct ref_store;
>  
>  /* refs backends */
>  
> +/* ref_store_init flags */
> +#define REF_STORE_READ		(1 << 0)

> +#define REF_STORE_WRITE		(1 << 1) /* can perform update operations */
> +#define REF_STORE_ODB		(1 << 2) /* has access to object database */
> +#define REF_STORE_MAIN		(1 << 3)
> +
>  /*
>   * Initialize the ref_store for the specified gitdir. These functions
>   * should call base_ref_store_init() to initialize the shared part of
>   * the ref_store and to record the ref_store for later lookup.
>   */
> -typedef struct ref_store *ref_store_init_fn(const char *gitdir);
> +typedef struct ref_store *ref_store_init_fn(const char *gitdir,
> +					    unsigned int flags);
>  
>  typedef int ref_init_db_fn(struct ref_store *refs, struct strbuf *err);