refs: make delete_refs() virtual

In the file-based backend, delete_refs has some special optimization
to deal with packed refs.  In other backends, we might be able to make
ref deletion faster by putting all deletions into a single
transaction.  So we need a special backend function for this.
Signed-off-by: NDavid Turner <dturner@twopensource.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>
Signed-off-by: NMichael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

refs.c

@@ -1532,3 +1532,10 @@ int initial_ref_transaction_commit(struct ref_transaction *transaction,
 
 	return refs->be->initial_transaction_commit(refs, transaction, err);
 }
+
+int delete_refs(struct string_list *refnames, unsigned int flags)
+{
+	struct ref_store *refs = get_ref_store(NULL);
+
+	return refs->be->delete_refs(refs, refnames, flags);
+}

refs/files-backend.c

@@ -2451,10 +2451,11 @@ static int delete_ref_loose(struct ref_lock *lock, int flag, struct strbuf *err)
 	return 0;
 }
 
-int delete_refs(struct string_list *refnames, unsigned int flags)
+static int files_delete_refs(struct ref_store *ref_store,
+			     struct string_list *refnames, unsigned int flags)
 {
 	struct files_ref_store *refs =
-		get_files_ref_store(NULL, "delete_refs");
+		files_downcast(ref_store, 0, "delete_refs");
 	struct strbuf err = STRBUF_INIT;
 	int i, result = 0;
 
@@ -4067,6 +4068,7 @@ struct ref_storage_be refs_be_files = {
 	files_pack_refs,
 	files_peel_ref,
 	files_create_symref,
+	files_delete_refs,
 
 	files_ref_iterator_begin,
 	files_read_raw_ref,

refs/refs-internal.h

@@ -490,6 +490,8 @@ typedef int create_symref_fn(struct ref_store *ref_store,
 			     const char *ref_target,
 			     const char *refs_heads_master,
 			     const char *logmsg);
+typedef int delete_refs_fn(struct ref_store *ref_store,
+			   struct string_list *refnames, unsigned int flags);
 
 /*
  * Iterate over the references in the specified ref_store that are
@@ -587,6 +589,7 @@ struct ref_storage_be {
 	pack_refs_fn *pack_refs;
 	peel_ref_fn *peel_ref;
 	create_symref_fn *create_symref;
+	delete_refs_fn *delete_refs;
 
 	ref_iterator_begin_fn *iterator_begin;
 	read_raw_ref_fn *read_raw_ref;