object-file: extract logic to approximate object count

In "builtin/gc.c" we have some logic that checks whether we need to
repack objects. This is done by counting the number of objects that we
have and checking whether it exceeds a certain threshold. We don't
really need an accurate object count though, which is why we only
open a single object directory shard and then extrapolate from there.

Extract this logic into a new function that is owned by the loose object
database source. This is done to prepare for a subsequent change, where
we'll introduce object counting on the object database source level.

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

1 files changed, 13 insertions, 0 deletions

diff --git a/object-file.h b/object-file.h
index ff6da65296..b870ea9fa8 100644
--- a/object-file.h
+++ b/object-file.h
@@ -139,6 +139,19 @@ int odb_source_loose_for_each_object(struct odb_source *source,
 				     void *cb_data,
 				     unsigned flags);
 
+/*
+ * Count the number of loose objects in this source.
+ *
+ * The object count is approximated by opening a single sharding directory for
+ * loose objects and scanning its contents. The result is then extrapolated by
+ * 256. This should generally work as a reasonable estimate given that the
+ * object hash is supposed to be indistinguishable from random.
+ *
+ * Returns 0 on success, a negative error code otherwise.
+ */
+int odb_source_loose_approximate_object_count(struct odb_source *source,
+					      unsigned long *out);
+
 /**
  * format_object_header() is a thin wrapper around s xsnprintf() that
  * writes the initial "<type> <obj-len>" part of the loose object