refs: add methods to init refs db

Alternate refs backends might not need the refs/heads directory and so
on, so we make ref db initialization part of the backend.

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

builtin/init-db.c

@@ -180,13 +180,7 @@ static int create_default_files(const char *template_path)
 	char junk[2];
 	int reinit;
 	int filemode;
-
-	/*
-	 * Create .git/refs/{heads,tags}
-	 */
-	safe_create_dir(git_path_buf(&buf, "refs"), 1);
-	safe_create_dir(git_path_buf(&buf, "refs/heads"), 1);
-	safe_create_dir(git_path_buf(&buf, "refs/tags"), 1);
+	struct strbuf err = STRBUF_INIT;
 
 	/* Just look for `init.templatedir` */
 	git_config(git_init_db_config, NULL);
@@ -210,11 +204,18 @@ static int create_default_files(const char *template_path)
 	 */
 	if (get_shared_repository()) {
 		adjust_shared_perm(get_git_dir());
-		adjust_shared_perm(git_path_buf(&buf, "refs"));
-		adjust_shared_perm(git_path_buf(&buf, "refs/heads"));
-		adjust_shared_perm(git_path_buf(&buf, "refs/tags"));
 	}
 
+	/*
+	 * We need to create a "refs" dir in any case so that older
+	 * versions of git can tell that this is a repository.
+	 */
+	safe_create_dir(git_path("refs"), 1);
+	adjust_shared_perm(git_path("refs"));
+
+	if (refs_init_db(&err))
+		die("failed to set up refs db: %s", err.buf);
+
 	/*
 	 * Create the default symlink from ".git/HEAD" to the "master"
 	 * branch, if it does not exist yet.

refs.c

@@ -1292,6 +1292,14 @@ static const char *resolve_ref_recursively(struct ref_store *refs,
 	return NULL;
 }
 
+/* backend functions */
+int refs_init_db(struct strbuf *err)
+{
+	struct ref_store *refs = get_ref_store(NULL);
+
+	return refs->be->init_db(refs, err);
+}
+
 const char *resolve_ref_unsafe(const char *refname, int resolve_flags,
 			       unsigned char *sha1, int *flags)
 {

refs.h

@@ -66,6 +66,8 @@ int ref_exists(const char *refname);
 
 int is_branch(const char *refname);
 
+extern int refs_init_db(struct strbuf *err);
+
 /*
  * If refname is a non-symbolic reference that refers to a tag object,
  * and the tag can be (recursively) dereferenced to a non-tag object,

refs/files-backend.c

@@ -4058,10 +4058,28 @@ static int files_reflog_expire(struct ref_store *ref_store,
 	return -1;
 }
 
+static int files_init_db(struct ref_store *ref_store, struct strbuf *err)
+{
+	/* Check validity (but we don't need the result): */
+	files_downcast(ref_store, 0, "init_db");
+
+	/*
+	 * Create .git/refs/{heads,tags}
+	 */
+	safe_create_dir(git_path("refs/heads"), 1);
+	safe_create_dir(git_path("refs/tags"), 1);
+	if (get_shared_repository()) {
+		adjust_shared_perm(git_path("refs/heads"));
+		adjust_shared_perm(git_path("refs/tags"));
+	}
+	return 0;
+}
+
 struct ref_storage_be refs_be_files = {
 	NULL,
 	"files",
 	files_ref_store_create,
+	files_init_db,
 	files_transaction_commit,
 	files_initial_transaction_commit,
 

refs/refs-internal.h

@@ -479,6 +479,8 @@ struct ref_store;
  */
 typedef struct ref_store *ref_store_init_fn(const char *submodule);
 
+typedef int ref_init_db_fn(struct ref_store *refs, struct strbuf *err);
+
 typedef int ref_transaction_commit_fn(struct ref_store *refs,
 				      struct ref_transaction *transaction,
 				      struct strbuf *err);
@@ -583,6 +585,7 @@ struct ref_storage_be {
 	struct ref_storage_be *next;
 	const char *name;
 	ref_store_init_fn *init;
+	ref_init_db_fn *init_db;
 	ref_transaction_commit_fn *transaction_commit;
 	ref_transaction_commit_fn *initial_transaction_commit;