refs: move `original_update_refname` to 'refs.c'

The files backend and the reftable backend implement
`original_update_refname` to obtain the original refname of the update.
Move it out to 'refs.c' and only expose it internally to the refs
library. This will be used in an upcoming commit to also introduce
another common functionality for the two backends.

We also rename the function to `ref_update_original_update_refname` to
keep it consistent with the upcoming other 'ref_update_*' functions
that'll be introduced.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/refs.c b/refs.c
index 9d722d798a..990703ed16 100644
--- a/refs.c
+++ b/refs.c
@@ -2814,3 +2814,11 @@ int copy_existing_ref(const char *oldref, const char *newref, const char *logmsg
 {
 	return refs_copy_existing_ref(get_main_ref_store(the_repository), oldref, newref, logmsg);
 }
+
+const char *ref_update_original_update_refname(struct ref_update *update)
+{
+	while (update->parent_update)
+		update = update->parent_update;
+
+	return update->refname;
+}