odb/source: make freshen_object() function pluggable

Introduce a new callback function in `struct odb_source` to make the
function pluggable.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

odb.c

@@ -959,18 +959,10 @@ int odb_freshen_object(struct object_database *odb,
 		       const struct object_id *oid)
 {
 	struct odb_source *source;
-
 	odb_prepare_alternates(odb);
-	for (source = odb->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-
-		if (packfile_store_freshen_object(files->packed, oid))
+	for (source = odb->sources; source; source = source->next)
+		if (odb_source_freshen_object(source, oid))
 			return 1;
-
-		if (odb_source_loose_freshen_object(source, oid))
-			return 1;
-	}
-
 	return 0;
 }
 

odb/source-files.c

@@ -88,6 +88,16 @@ static int odb_source_files_for_each_object(struct odb_source *source,
 	return 0;
 }
 
+static int odb_source_files_freshen_object(struct odb_source *source,
+					   const struct object_id *oid)
+{
+	struct odb_source_files *files = odb_source_files_downcast(source);
+	if (packfile_store_freshen_object(files->packed, oid) ||
+	    odb_source_loose_freshen_object(source, oid))
+		return 1;
+	return 0;
+}
+
 struct odb_source_files *odb_source_files_new(struct object_database *odb,
 					      const char *path,
 					      bool local)
@@ -105,6 +115,7 @@ struct odb_source_files *odb_source_files_new(struct object_database *odb,
 	files->base.read_object_info = odb_source_files_read_object_info;
 	files->base.read_object_stream = odb_source_files_read_object_stream;
 	files->base.for_each_object = odb_source_files_for_each_object;
+	files->base.freshen_object = odb_source_files_freshen_object;
 
 	/*
 	 * Ideally, we would only ever store absolute paths in the source. This

odb/source.h

@@ -186,6 +186,18 @@ struct odb_source {
 			       odb_for_each_object_cb cb,
 			       void *cb_data,
 			       unsigned flags);
+
+	/*
+	 * This callback is expected to freshen the given object so that its
+	 * last access time is set to the current time. This is used to ensure
+	 * that objects that are recent will not get garbage collected even if
+	 * they were unreachable.
+	 *
+	 * Returns 0 in case the object does not exist, 1 in case the object
+	 * has been freshened.
+	 */
+	int (*freshen_object)(struct odb_source *source,
+			      const struct object_id *oid);
 };
 
 /*
@@ -297,4 +309,15 @@ static inline int odb_source_for_each_object(struct odb_source *source,
 	return source->for_each_object(source, request, cb, cb_data, flags);
 }
 
+/*
+ * Freshen an object in the object database by updating its timestamp.
+ * Returns 1 in case the object has been freshened, 0 in case the object does
+ * not exist.
+ */
+static inline int odb_source_freshen_object(struct odb_source *source,
+					    const struct object_id *oid)
+{
+	return source->freshen_object(source, oid);
+}
+
 #endif