object-file: introduce struct odb_source_loose

Currently, all state that relates to loose objects is held directly by
the `struct odb_source`. Introduce a new `struct odb_source_loose` to
hold the state instead so that it is entirely self-contained.

This structure will eventually morph into the backend for accessing
loose objects. As such, this is part of the refactorings to introduce
pluggable object databases.

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

Author: pks-t

object-file.c

@@ -1995,3 +1995,16 @@ void object_file_transaction_commit(struct odb_transaction *transaction)
 	transaction->odb->transaction = NULL;
 	free(transaction);
 }
+
+struct odb_source_loose *odb_source_loose_new(struct odb_source *source)
+{
+	struct odb_source_loose *loose;
+	CALLOC_ARRAY(loose, 1);
+	loose->source = source;
+	return loose;
+}
+
+void odb_source_loose_free(struct odb_source_loose *loose)
+{
+	free(loose);
+}

object-file.h

@@ -18,6 +18,13 @@ int index_path(struct index_state *istate, struct object_id *oid, const char *pa
 
 struct odb_source;
 
+struct odb_source_loose {
+	struct odb_source *source;
+};
+
+struct odb_source_loose *odb_source_loose_new(struct odb_source *source);
+void odb_source_loose_free(struct odb_source_loose *loose);
+
 /*
  * Populate and return the loose object cache array corresponding to the
  * given object ID.

odb.c

@@ -151,6 +151,7 @@ struct odb_source *odb_source_new(struct object_database *odb,
 	source->odb = odb;
 	source->local = local;
 	source->path = xstrdup(path);
+	source->loose = odb_source_loose_new(source);
 
 	return source;
 }
@@ -368,6 +369,7 @@ struct odb_source *odb_set_temporary_primary_source(struct object_database *odb,
 static void odb_source_free(struct odb_source *source)
 {
 	free(source->path);
+	odb_source_loose_free(source->loose);
 	odb_clear_loose_cache(source);
 	loose_object_map_clear(&source->loose_map);
 	free(source);

odb.h

@@ -48,6 +48,9 @@ struct odb_source {
 	/* Object database that owns this object source. */
 	struct object_database *odb;
 
+	/* Private state for loose objects. */
+	struct odb_source_loose *loose;
+
 	/*
 	 * Used to store the results of readdir(3) calls when we are OK
 	 * sacrificing accuracy due to races for speed. That includes