From 3af95e3dd472e342f1d8d108e079e9b552509d23 Mon Sep 17 00:00:00 2001
From: Pavel Kirienko <pavel.kirienko@gmail.com>
Date: Tue, 5 May 2015 11:31:55 +0300
Subject: [PATCH] Log initialization fix

---
 .../uc_dynamic_node_id_allocation_server.cpp  | 26 ++++++++++++-------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/libuavcan/src/protocol/uc_dynamic_node_id_allocation_server.cpp b/libuavcan/src/protocol/uc_dynamic_node_id_allocation_server.cpp
index c358b80f88..55045e505a 100644
--- a/libuavcan/src/protocol/uc_dynamic_node_id_allocation_server.cpp
+++ b/libuavcan/src/protocol/uc_dynamic_node_id_allocation_server.cpp
@@ -228,10 +228,24 @@ int Log::initEmptyLogStorage()
 {
     MarshallingStorageDecorator io(storage_);
 
-    // Initializing last index
+    /*
+     * Writing the zero entry - it must always be default-initialized
+     */
+    entries_[0] = protocol::dynamic_node_id::server::Entry();
+    int res = writeEntryToStorage(0, entries_[0]);
+    if (res < 0)
+    {
+        return res;
+    }
+
+    /*
+     * Initializing last index
+     * Last index must be written AFTER the zero entry, otherwise if the write fails here the storage will be
+     * left in an inconsistent state.
+     */
     last_index_ = 0;
     uint32_t stored_index = 0;
-    int res = io.setAndGetBack(getLastIndexKey(), stored_index);
+    res = io.setAndGetBack(getLastIndexKey(), stored_index);
     if (res < 0)
     {
         return res;
@@ -241,14 +255,6 @@ int Log::initEmptyLogStorage()
         return -ErrFailure;
     }
 
-    // Writing the zero entry - it must always be default-initialized
-    entries_[0] = protocol::dynamic_node_id::server::Entry();
-    res = writeEntryToStorage(0, entries_[0]);
-    if (res < 0)
-    {
-        return res;
-    }
-
     return 0;
 }