Handle RestoreChildren() failures and ensure to refresh the non-volatile settings. (#1543)

This commit makes the following changes:

- It updates `RestoreChildren()` to detect error cases where the
  saved children info is invalid or if there are more children
  stored in non-volatile settings than can be restored.

- In case of such errors, it is ensured that the content in
  non-volatile memory is refreshed (through newly introduced method
  `MleRouter::RefreshStoredChildren()`) so that it stays in sync
  with the child table.

src/core/thread/mle.cpp

@@ -304,7 +304,23 @@ ThreadError Mle::Restore(void)
     {
         mNetif.GetMle().SetRouterId(GetRouterId(GetRloc16()));
         mNetif.GetMle().SetPreviousPartitionId(networkInfo.mPreviousPartitionId);
-        mNetif.GetMle().RestoreChildren();
+
+        switch (mNetif.GetMle().RestoreChildren())
+        {
+        // If there are more saved children in non-volatile settings
+        // than could be restored or the values in the settings are
+        // invalid, erase all the children info in the settings and
+        // refresh the info to ensure that the non-volatile settings
+        // stay in sync with the child table.
+
+        case kThreadError_Failed:
+        case kThreadError_NoBufs:
+            mNetif.GetMle().RefreshStoredChildren();
+            break;
+
+        default:
+            break;
+        }
     }
 
 exit:

src/core/thread/mle_router.cpp

@@ -3398,7 +3398,7 @@ ThreadError MleRouter::RestoreChildren(void)
 {
     ThreadError error = kThreadError_None;
 
-    for (uint8_t i = 0; i < kMaxChildren; i++)
+    for (uint8_t i = 0; ; i++)
     {
         Child *child;
         otChildInfo childInfo;
@@ -3407,7 +3407,7 @@ ThreadError MleRouter::RestoreChildren(void)
         length = sizeof(childInfo);
         SuccessOrExit(otPlatSettingsGet(mNetif.GetInstance(), kKeyChildInfo, i,
                                         reinterpret_cast<uint8_t *>(&childInfo), &length));
-        VerifyOrExit(length == sizeof(childInfo), ;);
+        VerifyOrExit(length == sizeof(childInfo), error = kThreadError_Failed);
 
         VerifyOrExit((child = NewChild()) != NULL, error = kThreadError_NoBufs);
         memset(child, 0, sizeof(*child));
@@ -3468,6 +3468,24 @@ exit:
     return error;
 }
 
+ThreadError MleRouter::RefreshStoredChildren(void)
+{
+    ThreadError error = kThreadError_None;
+
+    SuccessOrExit(error = otPlatSettingsDelete(mNetif.GetInstance(), kKeyChildInfo, -1));
+
+    for (uint8_t i = 0; i < kMaxChildren; i++)
+    {
+        if (mChildren[i].mState != Neighbor::kStateInvalid)
+        {
+            SuccessOrExit(error = StoreChild(mChildren[i].mValid.mRloc16));
+        }
+    }
+
+exit:
+    return error;
+}
+
 ThreadError MleRouter::GetChildInfo(Child &aChild, otChildInfo &aChildInfo)
 {
     ThreadError error = kThreadError_None;

src/core/thread/mle_router_ftd.hpp

@@ -389,7 +389,7 @@ public:
      *
      * @param[in]  aMaxChildren  The max children allowed value.
      *
-     * @retval  kThreadErrorNone           Successfully set the max.
+     * @retval  kThreadError_None          Successfully set the max.
      * @retval  kThreadError_InvalidArgs   If @p aMaxChildren is not in the range [1, kMaxChildren].
      * @retval  kThreadError_InvalidState  If MLE has already been started.
      *
@@ -399,8 +399,9 @@ public:
     /**
      * This method restores children information from non-volatile memory.
      *
-     * @retval  kThreadErrorNone      Successfully restores children information.
-     * @retval  kThreadError_NoBufs   Insufficient available buffers to restore all children information.
+     * @retval  kThreadError_None     Successfully restored children information.
+     * @retval  kThreadError_Failed   The saved child info in non-volatile memory is invalid.
+     * @retval  kThreadError_NoBufs   More children in settings than max children.
      *
      */
     ThreadError RestoreChildren(void);
@@ -410,7 +411,7 @@ public:
      *
      * @param[in]  aChildRloc16   The child RLOC16 to remove.
      *
-     * @retval  kThreadErrorNone        Successfully remove child.
+     * @retval  kThreadError_None       Successfully remove child.
      * @retval  kThreadError_NotFound   There is no specified child stored in non-volatile memory.
      *
      */
@@ -421,12 +422,22 @@ public:
      *
      * @param[in]  aChildRloc16   The child RLOC16 to store.
      *
-     * @retval  kThreadErrorNone      Successfully store child.
+     * @retval  kThreadError_None     Successfully store child.
      * @retval  kThreadError_NoBufs   Insufficient available buffers to store child.
      *
      */
     ThreadError StoreChild(uint16_t aChildRloc16);
 
+    /**
+     * This method refreshes all the saved children information in non-volatile memory by first erasing any saved
+     * child information in non-volatile memory and then saving all children info.
+     *
+     * @retval  kThreadError_None     Successfully refreshed all children info in non-volatile memory
+     * @retval  kThreadError_NoBufs   Insufficient available buffers to store child.
+     *
+     */
+    ThreadError RefreshStoredChildren(void);
+
     /**
      * This method returns a pointer to a Neighbor object.
      *

src/core/thread/mle_router_mtd.hpp

@@ -113,6 +113,7 @@ public:
     ThreadError RestoreChildren(void) {return kThreadError_NotImplemented; }
     ThreadError RemoveStoredChild(uint16_t) {return kThreadError_NotImplemented; }
     ThreadError StoreChild(uint16_t) {return kThreadError_NotImplemented; }
+    ThreadError RefreshStoredChildren(void) { return kThreadError_NotImplemented; }
 
     Neighbor *GetNeighbor(uint16_t aAddress) { return Mle::GetNeighbor(aAddress); }
     Neighbor *GetNeighbor(const Mac::ExtAddress &aAddress) { return Mle::GetNeighbor(aAddress); }