odb/source-packed: start converting to a proper struct odb_source

Start converting `struct odb_source_packed` into a proper pluggable
`struct odb_source` by embedding the base struct and assigning it the
new `ODB_SOURCE_PACKED` type. Furthermore, wire up lifecycle management
of this source by implementing the `free` callback and taking ownership
of the chdir notifications.

Note that the packed source is not yet functional as a standalone `struct
odb_source`, as it's missing all of the callback implementations. These
will be wired up in subsequent commits.

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

odb/source-files.c

@@ -29,7 +29,7 @@ static void odb_source_files_free(struct odb_source *source)
 	struct odb_source_files *files = odb_source_files_downcast(source);
 	chdir_notify_unregister(NULL, odb_source_files_reparent, files);
 	odb_source_free(&files->loose->base);
-	packfile_store_free(files->packed);
+	odb_source_free(&files->packed->base);
 	odb_source_release(&files->base);
 	free(files);
 }

odb/source-packed.c

@@ -1,11 +1,50 @@
 #include "git-compat-util.h"
+#include "abspath.h"
+#include "chdir-notify.h"
 #include "odb/source-packed.h"
+#include "packfile.h"
+
+static void odb_source_packed_reparent(const char *name UNUSED,
+				       const char *old_cwd,
+				       const char *new_cwd,
+				       void *cb_data)
+{
+	struct odb_source_packed *packed = cb_data;
+	char *path = reparent_relative_path(old_cwd, new_cwd,
+					    packed->base.path);
+	free(packed->base.path);
+	packed->base.path = path;
+}
+
+static void odb_source_packed_free(struct odb_source *source)
+{
+	struct odb_source_packed *packed = odb_source_packed_downcast(source);
+
+	chdir_notify_unregister(NULL, odb_source_packed_reparent, packed);
+
+	for (struct packfile_list_entry *e = packed->packs.head; e; e = e->next)
+		free(e->pack);
+	packfile_list_clear(&packed->packs);
+
+	strmap_clear(&packed->packs_by_path, 0);
+	odb_source_release(&packed->base);
+	free(packed);
+}
 
 struct odb_source_packed *odb_source_packed_new(struct odb_source_files *parent)
 {
-	struct odb_source_packed *store;
-	CALLOC_ARRAY(store, 1);
-	store->files = parent;
-	strmap_init(&store->packs_by_path);
-	return store;
+	struct odb_source_packed *packed;
+
+	CALLOC_ARRAY(packed, 1);
+	odb_source_init(&packed->base, parent->base.odb, ODB_SOURCE_PACKED,
+			parent->base.path, parent->base.local);
+	packed->files = parent;
+	strmap_init(&packed->packs_by_path);
+
+	packed->base.free = odb_source_packed_free;
+
+	if (!is_absolute_path(parent->base.path))
+		chdir_notify_register(NULL, odb_source_packed_reparent, packed);
+
+	return packed;
 }

odb/source-packed.h

@@ -9,6 +9,7 @@
  * A store that manages packfiles for a given object database.
  */
 struct odb_source_packed {
+	struct odb_source base;
 	struct odb_source_files *files;
 
 	/*
@@ -69,4 +70,15 @@ struct odb_source_packed {
  */
 struct odb_source_packed *odb_source_packed_new(struct odb_source_files *parent);
 
+/*
+ * Cast the given object database source to the packed backend. This will cause
+ * a BUG in case the source doesn't use this backend.
+ */
+static inline struct odb_source_packed *odb_source_packed_downcast(struct odb_source *source)
+{
+	if (source->type != ODB_SOURCE_PACKED)
+		BUG("trying to downcast source of type '%d' to packed", source->type);
+	return container_of(source, struct odb_source_packed, base);
+}
+
 #endif

odb/source.h

@@ -17,6 +17,9 @@ enum odb_source_type {
 	/* The "loose" backend that uses loose objects, only. */
 	ODB_SOURCE_LOOSE,
 
+	/* The "packed" backend that uses packfiles. */
+	ODB_SOURCE_PACKED,
+
 	/* The "in-memory" backend that stores objects in memory. */
 	ODB_SOURCE_INMEMORY,
 };

packfile.c

@@ -2749,16 +2749,6 @@ int parse_pack_header_option(const char *in, unsigned char *out, unsigned int *l
 	return 0;
 }
 
-void packfile_store_free(struct odb_source_packed *store)
-{
-	for (struct packfile_list_entry *e = store->packs.head; e; e = e->next)
-		free(e->pack);
-	packfile_list_clear(&store->packs);
-
-	strmap_clear(&store->packs_by_path, 0);
-	free(store);
-}
-
 void packfile_store_close(struct odb_source_packed *store)
 {
 	for (struct packfile_list_entry *e = store->packs.head; e; e = e->next) {

packfile.h

@@ -55,12 +55,6 @@ struct packed_git {
 	char pack_name[FLEX_ARRAY]; /* more */
 };
 
-/*
- * Free the packfile store and all its associated state. All packfiles
- * tracked by the store will be closed.
- */
-void packfile_store_free(struct odb_source_packed *store);
-
 /*
  * Close all packfiles associated with this store. The packfiles won't be
  * free'd, so they can be re-opened at a later point in time.