ref-cache: introduce a new type, ref_cache

For now, it just wraps a `ref_entry *` that points at the root of the
tree. Soon it will hold more information.

Add two new functions, `create_ref_cache()` and `free_ref_cache()`.
Make `free_ref_entry()` private.

Change files-backend to use this type to hold its caches.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs/files-backend.c

@@ -44,7 +44,7 @@ static int entry_resolves_to_object(struct ref_entry *entry)
 }
 
 struct packed_ref_cache {
-	struct ref_entry *root;
+	struct ref_cache *cache;
 
 	/*
 	 * Count of references to the data structure in this instance,
@@ -79,7 +79,7 @@ struct files_ref_store {
 	char *gitcommondir;
 	char *packed_refs_path;
 
-	struct ref_entry *loose;
+	struct ref_cache *loose;
 	struct packed_ref_cache *packed;
 };
 
@@ -101,7 +101,7 @@ static void acquire_packed_ref_cache(struct packed_ref_cache *packed_refs)
 static int release_packed_ref_cache(struct packed_ref_cache *packed_refs)
 {
 	if (!--packed_refs->referrers) {
-		free_ref_entry(packed_refs->root);
+		free_ref_cache(packed_refs->cache);
 		stat_validity_clear(&packed_refs->validity);
 		free(packed_refs);
 		return 1;
@@ -125,7 +125,7 @@ static void clear_packed_ref_cache(struct files_ref_store *refs)
 static void clear_loose_ref_cache(struct files_ref_store *refs)
 {
 	if (refs->loose) {
-		free_ref_entry(refs->loose);
+		free_ref_cache(refs->loose);
 		refs->loose = NULL;
 	}
 }
@@ -386,11 +386,12 @@ static struct packed_ref_cache *get_packed_ref_cache(struct files_ref_store *ref
 
 		refs->packed = xcalloc(1, sizeof(*refs->packed));
 		acquire_packed_ref_cache(refs->packed);
-		refs->packed->root = create_dir_entry(refs, "", 0, 0);
+		refs->packed->cache = create_ref_cache(refs);
+		refs->packed->cache->root->flag &= ~REF_INCOMPLETE;
 		f = fopen(packed_refs_file, "r");
 		if (f) {
 			stat_validity_update(&refs->packed->validity, fileno(f));
-			read_packed_refs(f, get_ref_dir(refs->packed->root));
+			read_packed_refs(f, get_ref_dir(refs->packed->cache->root));
 			fclose(f);
 		}
 	}
@@ -399,7 +400,7 @@ static struct packed_ref_cache *get_packed_ref_cache(struct files_ref_store *ref
 
 static struct ref_dir *get_packed_ref_dir(struct packed_ref_cache *packed_ref_cache)
 {
-	return get_ref_dir(packed_ref_cache->root);
+	return get_ref_dir(packed_ref_cache->cache->root);
 }
 
 static struct ref_dir *get_packed_refs(struct files_ref_store *refs)
@@ -514,14 +515,19 @@ static struct ref_dir *get_loose_refs(struct files_ref_store *refs)
 		 * are about to read the only subdirectory that can
 		 * hold references:
 		 */
-		refs->loose = create_dir_entry(refs, "", 0, 0);
+		refs->loose = create_ref_cache(refs);
+
+		/* We're going to fill the top level ourselves: */
+		refs->loose->root->flag &= ~REF_INCOMPLETE;
+
 		/*
-		 * Create an incomplete entry for "refs/":
+		 * Add an incomplete entry for "refs/" (to be filled
+		 * lazily):
 		 */
-		add_entry_to_dir(get_ref_dir(refs->loose),
+		add_entry_to_dir(get_ref_dir(refs->loose->root),
 				 create_dir_entry(refs, "refs/", 5, 1));
 	}
-	return get_ref_dir(refs->loose);
+	return get_ref_dir(refs->loose->root);
 }
 
 /*

refs/ref-cache.c

@@ -63,9 +63,17 @@ struct ref_entry *create_ref_entry(const char *refname,
 	return ref;
 }
 
+struct ref_cache *create_ref_cache(struct files_ref_store *refs)
+{
+	struct ref_cache *ret = xcalloc(1, sizeof(*ret));
+
+	ret->root = create_dir_entry(refs, "", 0, 1);
+	return ret;
+}
+
 static void clear_ref_dir(struct ref_dir *dir);
 
-void free_ref_entry(struct ref_entry *entry)
+static void free_ref_entry(struct ref_entry *entry)
 {
 	if (entry->flag & REF_DIR) {
 		/*
@@ -77,6 +85,12 @@ void free_ref_entry(struct ref_entry *entry)
 	free(entry);
 }
 
+void free_ref_cache(struct ref_cache *cache)
+{
+	free_ref_entry(cache->root);
+	free(cache);
+}
+
 /*
  * Clear and free all entries in dir, recursively.
  */

refs/ref-cache.h

@@ -1,6 +1,10 @@
 #ifndef REFS_REF_CACHE_H
 #define REFS_REF_CACHE_H
 
+struct ref_cache {
+	struct ref_entry *root;
+};
+
 /*
  * Information used (along with the information in ref_entry) to
  * describe a single cached reference.  This data structure only
@@ -165,7 +169,16 @@ struct ref_entry *create_ref_entry(const char *refname,
 				   const unsigned char *sha1, int flag,
 				   int check_name);
 
-void free_ref_entry(struct ref_entry *entry);
+/*
+ * Return a pointer to a new `ref_cache`. Its top-level starts out
+ * marked incomplete.
+ */
+struct ref_cache *create_ref_cache(struct files_ref_store *refs);
+
+/*
+ * Free the `ref_cache` and all of its associated data.
+ */
+void free_ref_cache(struct ref_cache *cache);
 
 /*
  * Add a ref_entry to the end of dir (unsorted).  Entry is always