[PATCH 04/17] odb: introduce parent pointers

[Patrick Steinhardt <ps@pks.im>]

In subsequent commits we'll get rid of our use of `the_repository` in
"odb.c" in favor of explicitly passing in a `struct object_database` or
a `struct odb_backend`. In some cases though we'll need access to the
repository, for example to read a config value from it, but we don't
have a way to access the repository owning a specific object database.

Introduce parent pointers for `struct object_database` to its owning
repository as well as for `struct odb_backend` to its owning object
database, which will allow us to adapt those use cases.

Note that this change requires us to pass through the object database to
`link_alt_odb_entry()` so that we can set up the parent pointers for any
alternative backends there. The callchain is adapted to pass through the
object database accordingly.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 odb.c | 43 +++++++++++++++++++++++++------------------
 odb.h |  6 ++++++
 2 files changed, 31 insertions(+), 18 deletions(-)

diff --git a/odb.c b/odb.c
index 435f532a9c4..67207ce636d 100644
--- a/odb.c
+++ b/odb.c
@@ -135,11 +135,15 @@ static int alt_odb_usable(struct object_database *o,
  * of the object ID, an extra slash for the first level indirection, and
  * the terminating NUL.
  */
-static void read_info_alternates(struct repository *r,
+static void read_info_alternates(struct object_database *odb,
 				 const char *relative_base,
 				 int depth);
-static int link_alt_odb_entry(struct repository *r, const struct strbuf *entry,
-	const char *relative_base, int depth, const char *normalized_objdir)
+
+static int link_alt_odb_entry(struct object_database *odb,
+			      const struct strbuf *entry,
+			      const char *relative_base,
+			      int depth,
+			      const char *normalized_objdir)
 {
 	struct odb_backend *backend;
 	struct strbuf pathbuf = STRBUF_INIT;
@@ -167,22 +171,23 @@ static int link_alt_odb_entry(struct repository *r, const struct strbuf *entry,
 	while (pathbuf.len && pathbuf.buf[pathbuf.len - 1] == '/')
 		strbuf_setlen(&pathbuf, pathbuf.len - 1);
 
-	if (!alt_odb_usable(r->objects, &pathbuf, normalized_objdir, &pos))
+	if (!alt_odb_usable(odb, &pathbuf, normalized_objdir, &pos))
 		goto error;
 
 	CALLOC_ARRAY(backend, 1);
+	backend->odb = odb;
 	/* pathbuf.buf is already in r->objects->backend_by_path */
 	backend->path = strbuf_detach(&pathbuf, NULL);
 
 	/* add the alternate entry */
-	*r->objects->backends_tail = backend;
-	r->objects->backends_tail = &(backend->next);
+	*odb->backends_tail = backend;
+	odb->backends_tail = &(backend->next);
 	backend->next = NULL;
-	assert(r->objects->backend_by_path);
-	kh_value(r->objects->backend_by_path, pos) = backend;
+	assert(odb->backend_by_path);
+	kh_value(odb->backend_by_path, pos) = backend;
 
 	/* recursively add alternates */
-	read_info_alternates(r, backend->path, depth + 1);
+	read_info_alternates(odb, backend->path, depth + 1);
 	ret = 0;
  error:
 	strbuf_release(&tmp);
@@ -219,7 +224,7 @@ static const char *parse_alt_odb_entry(const char *string,
 	return end;
 }
 
-static void link_alt_odb_entries(struct repository *r, const char *alt,
+static void link_alt_odb_entries(struct object_database *odb, const char *alt,
 				 int sep, const char *relative_base, int depth)
 {
 	struct strbuf objdirbuf = STRBUF_INIT;
@@ -234,20 +239,20 @@ static void link_alt_odb_entries(struct repository *r, const char *alt,
 		return;
 	}
 
-	strbuf_realpath(&objdirbuf, r->objects->backends->path, 1);
+	strbuf_realpath(&objdirbuf, odb->backends->path, 1);
 
 	while (*alt) {
 		alt = parse_alt_odb_entry(alt, sep, &entry);
 		if (!entry.len)
 			continue;
-		link_alt_odb_entry(r, &entry,
+		link_alt_odb_entry(odb, &entry,
 				   relative_base, depth, objdirbuf.buf);
 	}
 	strbuf_release(&entry);
 	strbuf_release(&objdirbuf);
 }
 
-static void read_info_alternates(struct repository *r,
+static void read_info_alternates(struct object_database *odb,
 				 const char *relative_base,
 				 int depth)
 {
@@ -261,7 +266,7 @@ static void read_info_alternates(struct repository *r,
 		return;
 	}
 
-	link_alt_odb_entries(r, buf.buf, '\n', relative_base, depth);
+	link_alt_odb_entries(odb, buf.buf, '\n', relative_base, depth);
 	strbuf_release(&buf);
 	free(path);
 }
@@ -303,7 +308,7 @@ void add_to_alternates_file(const char *reference)
 		if (commit_lock_file(&lock))
 			die_errno(_("unable to move new alternates file into place"));
 		if (the_repository->objects->loaded_alternates)
-			link_alt_odb_entries(the_repository, reference,
+			link_alt_odb_entries(the_repository->objects, reference,
 					     '\n', NULL, 0);
 	}
 	free(alts);
@@ -317,7 +322,7 @@ void add_to_alternates_memory(const char *reference)
 	 */
 	prepare_alt_odb(the_repository);
 
-	link_alt_odb_entries(the_repository, reference,
+	link_alt_odb_entries(the_repository->objects, reference,
 			     '\n', NULL, 0);
 }
 
@@ -336,6 +341,7 @@ struct odb_backend *set_temporary_primary_odb(const char *dir, int will_destroy)
 	 * alternate
 	 */
 	backend = xcalloc(1, sizeof(*backend));
+	backend->odb = the_repository->objects;
 	backend->path = xstrdup(dir);
 
 	/*
@@ -580,9 +586,9 @@ void prepare_alt_odb(struct repository *r)
 	if (r->objects->loaded_alternates)
 		return;
 
-	link_alt_odb_entries(r, r->objects->alternate_db, PATH_SEP, NULL, 0);
+	link_alt_odb_entries(r->objects, r->objects->alternate_db, PATH_SEP, NULL, 0);
 
-	read_info_alternates(r, r->objects->backends->path, 0);
+	read_info_alternates(r->objects, r->objects->backends->path, 0);
 	r->objects->loaded_alternates = 1;
 }
 
@@ -964,6 +970,7 @@ struct object_database *odb_new(struct repository *repo)
 	struct object_database *o = xmalloc(sizeof(*o));
 
 	memset(o, 0, sizeof(*o));
+	o->repo = repo;
 	INIT_LIST_HEAD(&o->packed_git_mru);
 	hashmap_init(&o->pack_map, pack_map_entry_cmp, NULL, 0);
 	pthread_mutex_init(&o->replace_mutex, NULL);
diff --git a/odb.h b/odb.h
index 5774e1d615b..1617a9bac2c 100644
--- a/odb.h
+++ b/odb.h
@@ -16,6 +16,9 @@ struct repository;
 struct odb_backend {
 	struct odb_backend *next;
 
+	/* Object database that owns this backend. */
+	struct object_database *odb;
+
 	/*
 	 * Used to store the results of readdir(3) calls when we are OK
 	 * sacrificing accuracy due to races for speed. That includes
@@ -93,6 +96,9 @@ struct cached_object_entry;
  * configured via alternates.
  */
 struct object_database {
+	/* Repository that owns this database. */
+	struct repository *repo;
+
 	/*
 	 * Set of all object directories; the main directory is first (and
 	 * cannot be NULL after initialization). Subsequent directories are

-- 
2.49.0.1045.g170613ef41.dirty