[PATCH v4 01/21] refs: add a backend method structure with transaction functions

[David Turner <dturner@twopensource.com>]

From: Ronnie Sahlberg <sahlberg@google.com>

Add a ref structure for storage backend methods. Start by adding a
method pointer for the transaction commit function.

Add a function set_refs_backend to switch between storage
backends. The files based storage backend is the default.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
Signed-off-by: David Turner <dturner@twopensource.com>
---
 refs.c               | 40 ++++++++++++++++++++++++++++++++++++++++
 refs.h               |  7 +++++++
 refs/files-backend.c | 10 ++++++++--
 refs/refs-internal.h | 12 ++++++++++++
 4 files changed, 67 insertions(+), 2 deletions(-)

diff --git a/refs.c b/refs.c
index e2d34b2..1c646f5 100644
--- a/refs.c
+++ b/refs.c
@@ -10,6 +10,39 @@
 #include "tag.h"
 
 /*
+ * We always have a files backend and it is the default.
+ */
+static struct ref_storage_be *the_refs_backend = &refs_be_files;
+/*
+ * List of all available backends
+ */
+static struct ref_storage_be *refs_backends = &refs_be_files;
+
+int set_ref_storage_backend(const char *name)
+{
+	struct ref_storage_be *be;
+
+	for (be = refs_backends; be; be = be->next)
+		if (!strcmp(be->name, name)) {
+			the_refs_backend = be;
+			return 0;
+		}
+	return 1;
+}
+
+int ref_storage_backend_exists(const char *name)
+{
+	struct ref_storage_be *be;
+
+	for (be = refs_backends; be; be = be->next)
+		if (!strcmp(be->name, name)) {
+			the_refs_backend = be;
+			return 1;
+		}
+	return 0;
+}
+
+/*
  * How to handle various characters in refnames:
  * 0: An acceptable character for refs
  * 1: End-of-component
@@ -1082,3 +1115,10 @@ int rename_ref_available(const char *oldname, const char *newname)
 	strbuf_release(&err);
 	return ret;
 }
+
+/* backend functions */
+int ref_transaction_commit(struct ref_transaction *transaction,
+			   struct strbuf *err)
+{
+	return the_refs_backend->transaction_commit(transaction, err);
+}
diff --git a/refs.h b/refs.h
index 3c3da29..5bc3fbc 100644
--- a/refs.h
+++ b/refs.h
@@ -508,4 +508,11 @@ extern int reflog_expire(const char *refname, const unsigned char *sha1,
 			 reflog_expiry_cleanup_fn cleanup_fn,
 			 void *policy_cb_data);
 
+/*
+ * Switch to an alternate ref storage backend.
+ */
+int set_ref_storage_backend(const char *name);
+
+int ref_storage_backend_exists(const char *name);
+
 #endif /* REFS_H */
diff --git a/refs/files-backend.c b/refs/files-backend.c
index b569762..2a73564 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -3146,8 +3146,8 @@ static int ref_update_reject_duplicates(struct string_list *refnames,
 	return 0;
 }
 
-int ref_transaction_commit(struct ref_transaction *transaction,
-			   struct strbuf *err)
+static int files_transaction_commit(struct ref_transaction *transaction,
+				    struct strbuf *err)
 {
 	int ret = 0, i;
 	int n = transaction->nr;
@@ -3533,3 +3533,9 @@ int reflog_expire(const char *refname, const unsigned char *sha1,
 	unlock_ref(lock);
 	return -1;
 }
+
+struct ref_storage_be refs_be_files = {
+	NULL,
+	"files",
+	files_transaction_commit,
+};
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index c7dded3..fc0e852 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -197,4 +197,16 @@ const char *find_descendant_ref(const char *dirname,
 
 int rename_ref_available(const char *oldname, const char *newname);
 
+/* refs backends */
+typedef int ref_transaction_commit_fn(struct ref_transaction *transaction,
+				      struct strbuf *err);
+
+struct ref_storage_be {
+	struct ref_storage_be *next;
+	const char *name;
+	ref_transaction_commit_fn *transaction_commit;
+};
+
+extern struct ref_storage_be refs_be_files;
+
 #endif /* REFS_REFS_INTERNAL_H */
-- 
2.4.2.749.g730654d-twtrsrc