[#3652] Remove the config history completely

- Removed revert() which makes no sense anymore.
- Since rollback() was significantly simplified, renamed it to
  clearStagingConfiguration().
- Removed kludgy ensureCurrentAllocated(). The only new required
  allocations are on constructor and on clear().

Author: andrei-pavel

src/bin/dhcp4/ctrl_dhcp4_srv.cc

@@ -179,7 +179,7 @@ ControlledDhcpv4Srv::loadConfigFile(const std::string& file_name) {
     } catch (const std::exception& ex) {
         // If configuration failed at any stage, we drop the staging
         // configuration and continue to use the previous one.
-        CfgMgr::instance().rollback();
+        CfgMgr::instance().clearStagingConfiguration();
 
         LOG_ERROR(dhcp4_logger, DHCP4_CONFIG_LOAD_FAIL)
             .arg(file_name).arg(ex.what());
@@ -372,7 +372,7 @@ ControlledDhcpv4Srv::commandConfigSetHandler(const string&,
     // We are starting the configuration process so we should remove any
     // staging configuration that has been created during previous
     // configuration attempts.
-    CfgMgr::instance().rollback();
+    CfgMgr::instance().clearStagingConfiguration();
 
     // Parse the logger configuration explicitly into the staging config.
     // Note this does not alter the current loggers, they remain in
@@ -478,7 +478,7 @@ ControlledDhcpv4Srv::commandConfigTestHandler(const string&,
     // We are starting the configuration process so we should remove any
     // staging configuration that has been created during previous
     // configuration attempts.
-    CfgMgr::instance().rollback();
+    CfgMgr::instance().clearStagingConfiguration();
 
     // Now we check the server proper.
     return (checkConfig(dhcp4));

src/bin/dhcp4/tests/config_parser_unittest.cc

@@ -751,7 +751,6 @@ class Dhcp4ParserTest : public LogContentTest {
             "\"dhcp-ddns\": { \"enable-updates\" : false }, "
             "\"option-def\": [ ], "
             "\"option-data\": [ ] }";
-        CfgMgr::instance().rollback();
         static_cast<void>(executeConfiguration(config,
                                                "reset configuration database"));
         // The default setting is to listen on all interfaces. In order to

src/bin/dhcp6/ctrl_dhcp6_srv.cc

@@ -182,7 +182,7 @@ ControlledDhcpv6Srv::loadConfigFile(const std::string& file_name) {
     } catch (const std::exception& ex) {
         // If configuration failed at any stage, we drop the staging
         // configuration and continue to use the previous one.
-        CfgMgr::instance().rollback();
+        CfgMgr::instance().clearStagingConfiguration();
 
         LOG_ERROR(dhcp6_logger, DHCP6_CONFIG_LOAD_FAIL)
             .arg(file_name).arg(ex.what());
@@ -375,7 +375,7 @@ ControlledDhcpv6Srv::commandConfigSetHandler(const string&,
     // We are starting the configuration process so we should remove any
     // staging configuration that has been created during previous
     // configuration attempts.
-    CfgMgr::instance().rollback();
+    CfgMgr::instance().clearStagingConfiguration();
 
     // Parse the logger configuration explicitly into the staging config.
     // Note this does not alter the current loggers, they remain in
@@ -481,7 +481,7 @@ ControlledDhcpv6Srv::commandConfigTestHandler(const string&,
     // We are starting the configuration process so we should remove any
     // staging configuration that has been created during previous
     // configuration attempts.
-    CfgMgr::instance().rollback();
+    CfgMgr::instance().clearStagingConfiguration();
 
     // Now we check the server proper.
     return (checkConfig(dhcp6));

src/bin/dhcp6/tests/config_parser_unittest.cc

@@ -881,7 +881,6 @@ class Dhcp6ParserTest : public LogContentTest {
             "\"dhcp-ddns\": { \"enable-updates\" : false }, "
             "\"option-def\": [ ], "
             "\"option-data\": [ ] }";
-        CfgMgr::instance().rollback();
         static_cast<void>(executeConfiguration(config,
                                                "reset configuration database"));
         // The default setting is to listen on all interfaces. In order to

src/lib/dhcpsrv/cfgmgr.cc

@@ -19,9 +19,10 @@ using namespace isc::util;
 namespace isc {
 namespace dhcp {
 
-// Value 0 effectively disables configuration history. Higher values can lead to proportionally
-// increased memory usage which can be extreme in case of sizable configurations.
-const size_t CfgMgr::CONFIG_LIST_SIZE = 0;
+CfgMgr::CfgMgr()
+    : datadir_(DHCP_DATA_DIR, true), d2_client_mgr_(new D2ClientMgr()),
+      configuration_(new SrvConfig()), family_(AF_INET) {
+}
 
 CfgMgr&
 CfgMgr::instance() {
@@ -41,7 +42,6 @@ CfgMgr::setDataDir(const std::string& datadir, bool unspecified) {
 
 void
 CfgMgr::setD2ClientConfig(D2ClientConfigPtr& new_config) {
-    ensureCurrentAllocated();
     // Note that D2ClientMgr::setD2Config() actually attempts to apply the
     // configuration by stopping its sender and opening a new one and so
     // forth per the new configuration.
@@ -69,40 +69,36 @@ CfgMgr::getD2ClientMgr() {
     return (*d2_client_mgr_);
 }
 
-void
-CfgMgr::ensureCurrentAllocated() {
-    if (!configuration_) {
-        configuration_.reset(new SrvConfig());
-        configs_.push_back(configuration_);
-    }
-}
-
 void
 CfgMgr::clear() {
+    if (staging_configuration_) {
+        staging_configuration_.reset();
+    }
     if (configuration_) {
         configuration_->removeStatistics();
-        configuration_.reset();
+        configuration_.reset(new SrvConfig());
     }
-    configs_.clear();
     external_configs_.clear();
     D2ClientConfigPtr d2_default_conf(new D2ClientConfig());
     setD2ClientConfig(d2_default_conf);
 }
 
 void
-CfgMgr::commit() {
-    ensureCurrentAllocated();
+CfgMgr::clearStagingConfiguration() {
+    staging_configuration_.reset();
+}
 
+void
+CfgMgr::commit() {
     // First we need to remove statistics. The new configuration can have fewer
     // subnets. Also, it may change subnet-ids. So we need to remove them all
     // and add them back.
     configuration_->removeStatistics();
 
-    bool promoted(false);
-    if (!configs_.empty() && !configs_.back()->sequenceEquals(*configuration_)) {
+    if (staging_configuration_ && !configuration_->sequenceEquals(*staging_configuration_)) {
         // Promote the staging configuration to the current configuration.
-        configuration_ = configs_.back();
-        promoted = true;
+        configuration_ = staging_configuration_;
+        staging_configuration_.reset();
     }
 
     // Set the last commit timestamp.
@@ -113,74 +109,20 @@ CfgMgr::commit() {
     configuration_->updateStatistics();
 
     configuration_->configureLowerLevelLibraries();
-
-    if (promoted) {
-        // Keep track of the maximum size of the configs history. Remove the oldest elements.
-        if (configs_.size() > CONFIG_LIST_SIZE) {
-            SrvConfigList::const_iterator it = configs_.begin();
-            std::advance(it, configs_.size() - CONFIG_LIST_SIZE);
-            configs_.erase(configs_.begin(), it);
-        }
-    }
-}
-
-void
-CfgMgr::rollback() {
-    ensureCurrentAllocated();
-    if (!configs_.empty() && !configuration_->sequenceEquals(*configs_.back())) {
-        configs_.pop_back();
-    }
-}
-
-void
-CfgMgr::revert(const size_t index) {
-    ensureCurrentAllocated();
-    if (index == 0) {
-        isc_throw(isc::OutOfRange, "invalid commit index 0 when reverting"
-                  " to an old configuration");
-    } else if (configs_.size() <= index) {
-        isc_throw(isc::OutOfRange, "unable to revert to commit index '"
-                  << index << "', only '" << (configs_.size() == 0 ? 0 : configs_.size() - 1)
-                  << "' previous commits available");
-    }
-
-    // Let's rollback an existing configuration to make sure that the last
-    // configuration on the list is the current one. Note that all remaining
-    // operations in this function should be exception free so there shouldn't
-    // be a problem that the revert operation fails and the staging
-    // configuration is destroyed by this rollback.
-    rollback();
-
-    if (!configs_.empty()) {
-        // Get the iterator to the current configuration and then advance to the
-        // desired one.
-        SrvConfigList::const_reverse_iterator it = configs_.rbegin();
-        std::advance(it, index);
-
-        // Copy the desired configuration to the new staging configuration. The
-        // staging configuration is re-created here because we rolled back earlier
-        // in this function.
-        (*it)->copy(*getStagingCfg());
-
-        // Make the staging configuration a current one.
-        commit();
-    }
 }
 
 SrvConfigPtr
 CfgMgr::getCurrentCfg() {
-    ensureCurrentAllocated();
     return (configuration_);
 }
 
 SrvConfigPtr
 CfgMgr::getStagingCfg() {
-    ensureCurrentAllocated();
-    if (configs_.empty() || configuration_->sequenceEquals(*configs_.back())) {
+    if (!staging_configuration_ || configuration_->sequenceEquals(*staging_configuration_)) {
         uint32_t sequence = configuration_->getSequence();
-        configs_.push_back(SrvConfigPtr(new SrvConfig(++sequence)));
+        staging_configuration_ = SrvConfigPtr(new SrvConfig(++sequence));
     }
-    return (configs_.back());
+    return (staging_configuration_);
 }
 
 SrvConfigPtr
@@ -230,15 +172,5 @@ CfgMgr::mergeIntoCfg(const SrvConfigPtr& target_config, const uint32_t seq) {
     }
 }
 
-CfgMgr::CfgMgr()
-    : datadir_(DHCP_DATA_DIR, true), d2_client_mgr_(new D2ClientMgr()), family_(AF_INET) {
-    // DHCP_DATA_DIR must be set set with -DDHCP_DATA_DIR="..." in Makefile.am
-    // Note: the definition of DHCP_DATA_DIR needs to include quotation marks
-    // See AM_CPPFLAGS definition in Makefile.am
-}
-
-CfgMgr::~CfgMgr() {
-}
-
 } // end of isc::dhcp namespace
 } // end of isc namespace

src/lib/dhcpsrv/cfgmgr.h

@@ -69,12 +69,6 @@ class DuplicateListeningIface : public Exception {
 /// @ref isc::dhcp::SimpleParser6::deriveParameters.
 class CfgMgr : public boost::noncopyable {
 public:
-
-    /// @brief A number of configurations held by @c CfgMgr.
-    ///
-    /// @todo Make it configurable.
-    static const size_t CONFIG_LIST_SIZE;
-
     /// @brief returns a single instance of Configuration Manager
     ///
     /// CfgMgr is a singleton and this method is the only way of
@@ -127,18 +121,13 @@ class CfgMgr : public boost::noncopyable {
     /// The following methods manage the process of preparing a configuration
     /// without affecting a currently used configuration and then committing
     /// the configuration to replace current configuration atomically.
-    /// They also allow for keeping a history of previous configurations so
-    /// as the @c CfgMgr can revert to the historical configuration when
-    /// required.
     ///
     /// @todo Migrate all configuration parameters to use the model supported
     /// by these functions.
     ///
-    /// @todo Make the size of the configurations history configurable.
-    ///
     //@{
 
-    /// @brief Removes current, staging and all previous configurations.
+    /// @brief Remove current, staging, and external configurations.
     ///
     /// This function removes all configurations, including current,
     /// staging and external configurations. It creates a new current
@@ -147,52 +136,18 @@ class CfgMgr : public boost::noncopyable {
     /// This function is exception safe.
     void clear();
 
-    /// @brief Commits the staging configuration.
-    ///
-    /// The staging configuration becomes current configuration when this
-    /// function is called. It removes the oldest configurations held in the
-    /// history so as the size of the list of configuration does not exceed
-    /// the @c CONFIG_LIST_SIZE.
+    /// @brief Remove staging configuration.
     ///
     /// This function is exception safe.
-    void commit();
+    void clearStagingConfiguration();
 
-    /// @brief Removes staging configuration.
+    /// @brief Commits the staging configuration.
     ///
-    /// This function should be called when there is a staging configuration
-    /// (likely created in the previous configuration attempt) but the entire
-    /// new configuration should be created. It removes the existing staging
-    /// configuration and the next call to @c CfgMgr::getStagingCfg will return a
-    /// fresh (default) configuration.
+    /// The staging configuration becomes current configuration when this
+    /// function is called.
     ///
     /// This function is exception safe.
-    void rollback();
-
-    /// @brief Reverts to one of the previous configurations.
-    ///
-    /// This function reverts to selected previous configuration. The previous
-    /// configuration is entirely copied to a new @c SrvConfig instance. This
-    /// new instance has a unique sequence id (sequence id is not copied). The
-    /// previous configuration (being copied) is not modified by this operation.
-    ///
-    /// The configuration to be copied is identified by the index value which
-    /// is the distance between the current (most recent) and desired
-    /// configuration. If the index is out of range an exception is thrown.
-    ///
-    /// @warning Revert operation will rollback any changes to the staging
-    /// configuration (if it exists).
-    ///
-    /// @warning This function requires that the entire previous configuration
-    /// is copied to the new configuration object. This is not working for
-    /// some of the complex configuration objects, e.g. subnets. Hence, the
-    /// "revert" operation is not really usable at this point.
-    ///
-    /// @param index A distance from the current configuration to the
-    /// past configuration to be reverted. The minimal value is 1 which points
-    /// to the nearest configuration.
-    ///
-    /// @throw isc::OutOfRange if the specified index is out of range.
-    void revert(const size_t index);
+    void commit();
 
     /// @brief Returns a pointer to the current configuration.
     ///
@@ -294,18 +249,9 @@ class CfgMgr : public boost::noncopyable {
     CfgMgr();
 
     /// @brief virtual destructor
-    virtual ~CfgMgr();
+    virtual ~CfgMgr() = default;
 
 private:
-
-    /// @brief Checks if current configuration is created and creates it if needed.
-    ///
-    /// This private method is called to ensure that the current configuration
-    /// is created. If current configuration is not set, it creates the
-    /// default current configuration.
-    void ensureCurrentAllocated();
-
-
     /// @brief Merges external configuration with the given sequence number
     /// into the specified configuration.
     ///
@@ -320,21 +266,16 @@ class CfgMgr : public boost::noncopyable {
     /// @brief Manages the DHCP-DDNS client and its configuration.
     D2ClientMgrPtr d2_client_mgr_;
 
-    /// @brief Server configuration
+    /// @brief Current server configuration
     ///
     /// This is a structure that will hold all configuration.
     /// @todo: migrate all other parameters to that structure.
     SrvConfigPtr configuration_;
 
-    /// @name Configuration List.
+    /// @brief Staging server configuration
     ///
-    //@{
-    /// @brief Server configuration list type.
-    typedef std::list<SrvConfigPtr> SrvConfigList;
-
-    /// @brief Container holding all previous and current configurations.
-    SrvConfigList configs_;
-    //@}
+    /// This is a structure that holds configuration until it is applied.
+    SrvConfigPtr staging_configuration_;
 
     /// @name Map of external configurations.
     ///