From cc098a7994a56a515311255ea7e4d0412b514879 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Carlos=20Mart=C3=ADn=20Nieto?= <cmn@dwim.me>
Date: Wed, 18 Dec 2013 19:41:01 +0100
Subject: wip

---
 include/git2/refs.h              | 10 ++++++++++
 include/git2/sys/refdb_backend.h | 38 ++++++++++++++++++++++++++++++++++++++
 include/git2/types.h             |  3 +++
 3 files changed, 51 insertions(+)

diff --git a/include/git2/refs.h b/include/git2/refs.h
index e2bfa9615..79cfcb3e3 100644
--- a/include/git2/refs.h
+++ b/include/git2/refs.h
@@ -569,6 +569,16 @@ GIT_EXTERN(int) git_reference_is_valid_name(const char *refname);
  */
 GIT_EXTERN(const char *) git_reference_shorthand(git_reference *ref);
 
+/**
+ * Start a new transaction for the specified reference
+ *
+ * Lock the reference and return a transaction that can be used to
+ * modify the reference under lock. You must either commit or rollback
+ * the transaction, or it will remain locked.
+ */
+GIT_EXTERN(int) git_reference_transaction_new(git_reference_transaction **out, git_repository *repo, const char *name);
+
+GIT_EXTERN(int) git_reference_transaction_set_reference((git_reference_transaction *txn, git_reference *ref);
 
 /** @} */
 GIT_END_DECL
diff --git a/include/git2/sys/refdb_backend.h b/include/git2/sys/refdb_backend.h
index 9cf5073fb..c61b9d642 100644
--- a/include/git2/sys/refdb_backend.h
+++ b/include/git2/sys/refdb_backend.h
@@ -56,6 +56,34 @@ struct git_reference_iterator {
 		git_reference_iterator *iter);
 };
 
+/**
+ * A transaction for a single reference
+ * 
+ * Any function returning a transaction must set the ref and (if
+ * available) reflog pointers.
+ */
+struct git_reference_transaction {
+	git_refdb *db;
+
+	git_reference *ref;
+	git_reflog *reflog;
+
+	/**
+	 * Apply the changes to the backend
+	 */
+	int (*commit)(git_reference_transaction *txn);
+
+	/**
+	 * Ignore any changes made in the transaction.
+	 */
+	int (*rollback)(git_reference_transaction *txn);
+
+	/**
+	 * Free the transaction
+	 */
+	void (*free)(git_reference_transaction *txn);
+}
+
 /** An instance for a custom backend */
 struct git_refdb_backend {
 	unsigned int version;
@@ -139,6 +167,16 @@ struct git_refdb_backend {
 	 * Remove a reflog.
 	 */
 	int (*reflog_delete)(git_refdb_backend *backend, const char *name);
+
+	/**
+	 * Create a new transaction
+	 */
+	int (*transaction_new)(git_reference_transaction *out, git_refdb_backend *backend, const char *name);
+
+	/**
+	 * Commit the changes made in a transaction
+	 */
+	int (*transaction_commit)(git_refdb_backend *backend, git_reference_transaction *txn);
 };
 
 #define GIT_REFDB_BACKEND_VERSION 1
diff --git a/include/git2/types.h b/include/git2/types.h
index 55505b110..e35b3f64d 100644
--- a/include/git2/types.h
+++ b/include/git2/types.h
@@ -171,6 +171,9 @@ typedef struct git_reference git_reference;
 /** Iterator for references */
 typedef struct git_reference_iterator  git_reference_iterator;
 
+/** Transaction on a single reference */
+typedef struct git_reference_transaction git_reference_transaction;
+
 /** Merge heads, the input to merge */
 typedef struct git_merge_head git_merge_head;
 
-- 
cgit v1.2.1