[logging] introduce log level override feature (openthread#12903)

This commit introduces a mechanism to temporarily override the log
level. The `Instance` class now provides `OverrideLogLevel()` and
`RestoreLogLevel()` methods. When an override is active, the
effective log level is the maximum of the original user-set level and
the override level. If `SetLogLevel()` is called while an override is
active, it updates the original level and the effective level is
recomputed.

This ensures that log messages are generated only when needed,
without permanently losing the user's original log level
configuration.

The feature is controlled by the new configuration macro
`OPENTHREAD_CONFIG_LOG_LEVEL_OVERRIDE_ENABLE`.

A new Nexus unit test `test_log_override.cpp` is added to validate
the behavior of these new feature.

Author: abtink

src/core/config/logging.h

@@ -197,6 +197,20 @@
 #define OPENTHREAD_CONFIG_LOG_MAX_SIZE 150
 #endif
 
+/**
+ * @def OPENTHREAD_CONFIG_LOG_LEVEL_OVERRIDE_ENABLE
+ *
+ * Define to 1 to enable the log level override feature and its associated APIs.
+ *
+ * This feature is used when `OPENTHREAD_CONFIG_LOG_LEVEL_DYNAMIC_ENABLE` is also enabled.
+ *
+ * When enabled, new mechanism is added to allow temporary override of the current log level (e.g., to increase the
+ * level to capture more detailed information) and subsequently restore it to the original user-specified level.
+ */
+#ifndef OPENTHREAD_CONFIG_LOG_LEVEL_OVERRIDE_ENABLE
+#define OPENTHREAD_CONFIG_LOG_LEVEL_OVERRIDE_ENABLE 0
+#endif
+
 /**
  * @}
  */

src/core/instance/instance.cpp

@@ -320,6 +320,11 @@ Instance::Instance(void)
 #endif
 #if OPENTHREAD_CONFIG_LOG_LEVEL_DYNAMIC_ENABLE
     , mLogLevel(static_cast<LogLevel>(OPENTHREAD_CONFIG_LOG_LEVEL_INIT))
+#if OPENTHREAD_CONFIG_LOG_LEVEL_OVERRIDE_ENABLE
+    , mOriginalLogLevel(kLogLevelNone)
+    , mOverrideLogLevel(kLogLevelNone)
+    , mIsLogLevelOverriden(false)
+#endif
 #if OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_ENABLE
     , mIsLogLevelSet(false)
 #else
@@ -591,20 +596,66 @@ Error Instance::SetLogLevel(LogLevel aLogLevel)
 #if OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_ENABLE && !OPENTHREAD_CONFIG_LOG_INSTANCE_AWARE_API_ENABLE
     ExitNow(error = kErrorNotCapable);
 #else
+#if OPENTHREAD_CONFIG_LOG_LEVEL_OVERRIDE_ENABLE
+    if (mIsLogLevelOverriden)
+    {
+        mOriginalLogLevel = aLogLevel;
+        aLogLevel         = Max(aLogLevel, mOverrideLogLevel);
+    }
+#endif
     VerifyOrExit(mLogLevel != aLogLevel);
     mLogLevel = aLogLevel;
+    SignalLogLevelChange();
+#endif
 
+exit:
+    return error;
+}
+
+void Instance::SignalLogLevelChange(void)
+{
 #if OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_ENABLE
     mIsLogLevelSet = true;
 #else
     otPlatLogHandleLevelChanged(mLogLevel);
 #endif
+
     otPlatLogHandleLogLevelChanged(this, mLogLevel);
-#endif
+}
+
+#if OPENTHREAD_CONFIG_LOG_LEVEL_OVERRIDE_ENABLE
+void Instance::OverrideLogLevel(LogLevel aLogLevel)
+{
+    LogLevel logLevel;
+
+    if (!mIsLogLevelOverriden)
+    {
+        mOriginalLogLevel    = GetLogLevel();
+        mIsLogLevelOverriden = true;
+    }
+
+    mOverrideLogLevel = aLogLevel;
+
+    logLevel = Max(mOverrideLogLevel, mOriginalLogLevel);
+
+    VerifyOrExit(mLogLevel != logLevel);
+    mLogLevel = logLevel;
+    SignalLogLevelChange();
 
 exit:
-    return error;
+    return;
+}
+
+void Instance::RestoreLogLevel(void)
+{
+    VerifyOrExit(mIsLogLevelOverriden);
+    mIsLogLevelOverriden = false;
+    IgnoreError(SetLogLevel(mOriginalLogLevel));
+
+exit:
+    return;
 }
+#endif // OPENTHREAD_CONFIG_LOG_LEVEL_OVERRIDE_ENABLE
 
 #if OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_ENABLE
 Error Instance::SetGlobalLogLevel(LogLevel aLogLevel)

src/core/instance/instance.hpp

@@ -356,6 +356,31 @@ class Instance : public otInstance, private NonCopyable
      */
     Error SetLogLevel(LogLevel aLogLevel);
 
+#if OPENTHREAD_CONFIG_LOG_LEVEL_OVERRIDE_ENABLE
+    /**
+     * Overrides the current log level with a new one.
+     *
+     * The active log level will be the maximum of the original (user-set) log level and the override log level.
+     * If this is the first time an override is requested, the current log level is saved as the original log level.
+     *
+     * Subsequent calls to `SetLogLevel()` will update the original log level, and the active log level will be
+     * updated accordingly (again as the maximum of the new original and the override level).
+     *
+     * This method can be called multiple times to change the override log level.
+     *
+     * @param[in] aLogLevel  The override log level.
+     */
+    void OverrideLogLevel(LogLevel aLogLevel);
+
+    /**
+     * Restores the log level to its original (user-set) value.
+     *
+     * This clears the log level override state. If the log level is not currently overridden, calling this
+     * method has no effect.
+     */
+    void RestoreLogLevel(void);
+#endif // OPENTHREAD_CONFIG_LOG_LEVEL_OVERRIDE_ENABLE
+
 #if OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_ENABLE
     /**
      * Sets the global log level.
@@ -523,6 +548,9 @@ class Instance : public otInstance, private NonCopyable
     Instance(void);
     void AfterInit(void);
 #endif
+#if OPENTHREAD_CONFIG_LOG_LEVEL_DYNAMIC_ENABLE
+    void SignalLogLevelChange(void);
+#endif
 
     //-----------------------------------------------------------------------------------------------------------------
     // `static` variables
@@ -866,6 +894,11 @@ class Instance : public otInstance, private NonCopyable
 
 #if OPENTHREAD_CONFIG_LOG_LEVEL_DYNAMIC_ENABLE
     LogLevel mLogLevel;
+#if OPENTHREAD_CONFIG_LOG_LEVEL_OVERRIDE_ENABLE
+    LogLevel mOriginalLogLevel;
+    LogLevel mOverrideLogLevel;
+    bool     mIsLogLevelOverriden;
+#endif
 #if OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_ENABLE
     bool mIsLogLevelSet;
 #endif

tests/nexus/CMakeLists.txt

@@ -382,6 +382,7 @@ ot_nexus_test(1_4_CS_TC_3 "cert;nexus")
 ot_nexus_test(border_admitter "core;nexus")
 ot_nexus_test(border_agent "core;nexus")
 ot_nexus_test(border_agent_tracker "core;nexus")
+ot_nexus_test(log_override "core;nexus")
 ot_nexus_test(discover_scan "core;nexus")
 ot_nexus_test(dtls "core;nexus")
 ot_nexus_test(form_join "core;nexus")

tests/nexus/openthread-core-nexus-config.h

@@ -89,6 +89,7 @@
 #define OPENTHREAD_CONFIG_LOG_LEVEL_DYNAMIC_ENABLE 1
 #define OPENTHREAD_CONFIG_LOG_LEVEL_INIT OT_LOG_LEVEL_CRIT
 #define OPENTHREAD_CONFIG_LOG_OUTPUT OPENTHREAD_CONFIG_LOG_OUTPUT_PLATFORM_DEFINED
+#define OPENTHREAD_CONFIG_LOG_LEVEL_OVERRIDE_ENABLE 1
 #define OPENTHREAD_CONFIG_LOG_PLATFORM 0
 #define OPENTHREAD_CONFIG_LOG_PREPEND_LEVEL 1
 #define OPENTHREAD_CONFIG_LOG_PREPEND_UPTIME 0

tests/nexus/test_log_override.cpp

@@ -0,0 +1,122 @@
+/*
+ *  Copyright (c) 2026, The OpenThread Authors.
+ *  All rights reserved.
+ *
+ *  Redistribution and use in source and binary forms, with or without
+ *  modification, are permitted provided that the following conditions are met:
+ *  1. Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *  2. Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *  3. Neither the name of the copyright holder nor the
+ *     names of its contributors may be used to endorse or promote products
+ *     derived from this software without specific prior written permission.
+ *
+ *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ *  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ *  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ *  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ *  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ *  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ *  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ *  POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+
+#include "platform/nexus_core.hpp"
+#include "platform/nexus_node.hpp"
+
+namespace ot {
+namespace Nexus {
+
+void TestLogOverride(void)
+{
+    Core  nexus;
+    Node &node = nexus.CreateNode();
+
+    Log("---------------------------------------------------------------------------------------");
+    Log("TestLogOverride");
+
+    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+    Log("Check initial log level");
+    VerifyOrQuit(node.Get<Instance>().GetLogLevel() == kLogLevelCrit);
+
+    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+    Log("Check OverrideLogLevel to a higher level");
+
+    node.Get<Instance>().OverrideLogLevel(kLogLevelInfo);
+    VerifyOrQuit(node.Get<Instance>().GetLogLevel() == kLogLevelInfo);
+
+    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+    Log("Check RestoreLogLevel");
+
+    node.Get<Instance>().RestoreLogLevel();
+    VerifyOrQuit(node.Get<Instance>().GetLogLevel() == kLogLevelCrit);
+
+    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+    Log("Check OverrideLogLevel with a level lower than the current level");
+
+    SuccessOrQuit(node.SetLogLevel(kLogLevelWarn));
+    VerifyOrQuit(node.Get<Instance>().GetLogLevel() == kLogLevelWarn);
+
+    node.Get<Instance>().OverrideLogLevel(kLogLevelCrit);
+
+    VerifyOrQuit(node.Get<Instance>().GetLogLevel() == kLogLevelWarn);
+
+    node.Get<Instance>().RestoreLogLevel();
+    VerifyOrQuit(node.Get<Instance>().GetLogLevel() == kLogLevelWarn);
+
+    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+    Log("Check user SetLogLevel while an override is active");
+
+    node.Get<Instance>().OverrideLogLevel(kLogLevelInfo);
+    VerifyOrQuit(node.Get<Instance>().GetLogLevel() == kLogLevelInfo);
+
+    SuccessOrQuit(node.SetLogLevel(kLogLevelCrit));
+
+    VerifyOrQuit(node.Get<Instance>().GetLogLevel() == kLogLevelInfo);
+
+    node.Get<Instance>().RestoreLogLevel();
+    VerifyOrQuit(node.Get<Instance>().GetLogLevel() == kLogLevelCrit);
+
+    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+    Log("Check multiple OverrideLogLevel calls");
+
+    node.Get<Instance>().OverrideLogLevel(kLogLevelWarn);
+    VerifyOrQuit(node.Get<Instance>().GetLogLevel() == kLogLevelWarn);
+
+    node.Get<Instance>().OverrideLogLevel(kLogLevelInfo);
+    VerifyOrQuit(node.Get<Instance>().GetLogLevel() == kLogLevelInfo);
+
+    node.Get<Instance>().RestoreLogLevel();
+    VerifyOrQuit(node.Get<Instance>().GetLogLevel() == kLogLevelCrit);
+
+    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+    Log("Check OverrideLogLevel and then SetLogLevel to a higher level than override");
+
+    node.Get<Instance>().OverrideLogLevel(kLogLevelWarn);
+    VerifyOrQuit(node.Get<Instance>().GetLogLevel() == kLogLevelWarn);
+
+    SuccessOrQuit(node.SetLogLevel(kLogLevelInfo));
+    VerifyOrQuit(node.Get<Instance>().GetLogLevel() == kLogLevelInfo);
+
+    node.Get<Instance>().RestoreLogLevel();
+    VerifyOrQuit(node.Get<Instance>().GetLogLevel() == kLogLevelInfo);
+}
+
+} // namespace Nexus
+} // namespace ot
+
+int main(void)
+{
+    ot::Nexus::TestLogOverride();
+    printf("All tests passed\n");
+    return 0;
+}

tests/toranj/openthread-core-toranj-config.h

@@ -147,6 +147,8 @@
 
 #define OPENTHREAD_CONFIG_LOG_LEVEL_DYNAMIC_ENABLE 1
 
+#define OPENTHREAD_CONFIG_LOG_LEVEL_OVERRIDE_ENABLE 1
+
 #define OPENTHREAD_CONFIG_LOG_PREPEND_UPTIME 1
 
 #define OPENTHREAD_CONFIG_LOG_PREPEND_LEVEL 1