*/
/*
- * Add a reference update to transaction. new_sha1 is the value that
- * the reference should have after the update, or null_sha1 if it should
- * be deleted. If old_sha1 is non-NULL, then it is the value
- * that the reference should have had before the update, or null_sha1 if
- * it must not have existed beforehand.
- * Function returns 0 on success and non-zero on failure. A failure to update
- * means that the transaction as a whole has failed and will need to be
- * rolled back.
+ * Add a reference update to transaction. new_sha1 is the value that
+ * the reference should have after the update, or null_sha1 if it
+ * should be deleted. If new_sha1 is NULL, then the reference is not
+ * changed at all. old_sha1 is the value that the reference must have
+ * before the update, or null_sha1 if it must not have existed
+ * beforehand. The old value is checked after the lock is taken to
+ * prevent races. If the old value doesn't agree with old_sha1, the
+ * whole transaction fails. If old_sha1 is NULL, then the previous
+ * value is not checked.
+ *
+ * Return 0 on success and non-zero on failure. Any failure in the
+ * transaction means that the transaction as a whole has failed and
+ * will need to be rolled back.
*/
int ref_transaction_update(struct ref_transaction *transaction,
const char *refname,
unsigned int flags, const char *msg,
struct strbuf *err);
+/*
+ * Verify, within a transaction, that refname has the value old_sha1,
+ * or, if old_sha1 is null_sha1, then verify that the reference
+ * doesn't exist. old_sha1 must be non-NULL. Function returns 0 on
+ * success and non-zero on failure. A failure to verify means that the
+ * transaction as a whole has failed and will need to be rolled back.
+ */
+int ref_transaction_verify(struct ref_transaction *transaction,
+ const char *refname,
+ const unsigned char *old_sha1,
+ unsigned int flags,
+ struct strbuf *err);
+
/*
* Commit all of the changes that have been queued in transaction, as
* atomically as possible.