alternates: provide helper for allocating alternate

Allocating a struct alternate_object_database is tricky, as
we must over-allocate the buffer to provide scratch space,
and then put in particular '/' and NUL markers.

Let's encapsulate this in a function so that the complexity
doesn't leak into callers (and so that we can modify it
later).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/cache.h b/cache.h
index 258ce6b..ece2c7c 100644
--- a/cache.h
+++ b/cache.h
@@ -1393,6 +1393,12 @@ typedef int alt_odb_fn(struct alternate_object_database *, void *);
 extern int foreach_alt_odb(alt_odb_fn, void*);
 
 /*
+ * Allocate a "struct alternate_object_database" but do _not_ actually
+ * add it to the list of alternates.
+ */
+struct alternate_object_database *alloc_alt_odb(const char *dir);
+
+/*
  * Add the directory to the on-disk alternates file; the new entry will also
  * take effect in the current process.
  */