[posix] minimize system initialization when dry-run option is set (#7031)

This commit adds a member mDryRun in otPlatformConfig, allowing the
app to initialize in 'DryRun' mode. In this mode, many modules won't
be initialized. For example, the settings file and the tun device.

Background:

The otbr-agent provides a way to query the RCP version in a single run
which we call as 'DryRun'. During this process, the full posix daemon
initialization will be done (including initialization of the settings
file, access the tun device, create the sock file, etc).  This will
cause such problem - In production, otbr-agent usually runs as a
service in some non-root user and is granted with the capability and
access it requires. But otbr-agent could sometimes also run by other
users to query the RCP version. For example, developers do that from
the console with the root user. In such case, otbr-agent will create
some files owned by the root user first. And then when the service
tries to start (with a non-root user), otbr-agent will find that it
doesn't have enough permission to open the file.

So in this commit, we try to prevent otbr-agent from touching any
files and other permission related stuffs if the DryRun option is set.

However it still needs to access the radio device (for example, the
'spi') since it needs to get the radio version. But accessing the
radio device with the root user doesn't affect the upcoming usage by
other non-root users.

src/posix/main.c

@@ -129,7 +129,6 @@ typedef struct PosixConfig
 {
     otPlatformConfig mPlatformConfig;    ///< Platform configuration.
     otLogLevel       mLogLevel;          ///< Debug level of logging.
-    bool             mIsDryRun;          ///< Dry run.
     bool             mPrintRadioVersion; ///< Whether to print radio firmware version.
     bool             mIsVerbose;         ///< Whether to print log to stderr.
 } PosixConfig;
@@ -232,7 +231,7 @@ static void ParseArg(int aArgCount, char *aArgVector[], PosixConfig *aConfig)
             aConfig->mPlatformConfig.mBackboneInterfaceName = optarg;
             break;
         case OT_POSIX_OPT_DRY_RUN:
-            aConfig->mIsDryRun = true;
+            aConfig->mPlatformConfig.mDryRun = true;
             break;
         case OT_POSIX_OPT_TIME_SPEED:
         {
@@ -308,7 +307,7 @@ static otInstance *InitInstance(PosixConfig *aConfig)
         syslog(LOG_INFO, "RCP version: %s", otPlatRadioGetVersionString(instance));
     }
 
-    if (aConfig->mIsDryRun)
+    if (aConfig->mPlatformConfig.mDryRun)
     {
         exit(OT_EXIT_SUCCESS);
     }

src/posix/platform/include/openthread/openthread-system.h

@@ -78,6 +78,8 @@ typedef struct otPlatformConfig
     uint8_t     mRadioUrlNum;                                  ///< Number of Radio URLs.
     int         mRealTimeSignal;                               ///< The real-time signal for microsecond timer.
     uint32_t    mSpeedUpFactor;                                ///< Speed up factor.
+    bool        mDryRun;                                       ///< If 'DryRun' is set, the posix daemon will exit
+                                                               ///< directly after initialization.
 } otPlatformConfig;
 
 /**

src/posix/platform/settings.cpp

@@ -54,6 +54,8 @@
 #include "common/code_utils.hpp"
 #include "common/encoding.hpp"
 
+#include "system.hpp"
+
 static const size_t kMaxFileNameSize = sizeof(OPENTHREAD_CONFIG_POSIX_SETTINGS_PATH) + 32;
 
 static int sSettingsFd = -1;
@@ -168,6 +170,9 @@ void otPlatSettingsInit(otInstance *aInstance)
 {
     otError error = OT_ERROR_NONE;
 
+    // Don't touch the settings file the system runs in dry-run mode.
+    VerifyOrExit(!IsSystemDryRun());
+
 #if OPENTHREAD_POSIX_CONFIG_SECURE_SETTINGS_ENABLE
     otPosixSecureSettingsInit(aInstance);
 #endif
@@ -233,6 +238,7 @@ otError otPlatSettingsGet(otInstance *aInstance, uint16_t aKey, int aIndex, uint
     const off_t size   = lseek(sSettingsFd, 0, SEEK_END);
     off_t       offset = lseek(sSettingsFd, 0, SEEK_SET);
 
+    VerifyOrExit(!IsSystemDryRun());
 #if OPENTHREAD_POSIX_CONFIG_SECURE_SETTINGS_ENABLE
     if (isCriticalKey(aKey))
     {
@@ -494,6 +500,12 @@ void otPlatRadioGetIeeeEui64(otInstance *aInstance, uint8_t *aIeeeEui64)
     memset(aIeeeEui64, 0, sizeof(uint64_t));
 }
 
+// Stub implementation for testing
+bool IsSystemDryRun(void)
+{
+    return false;
+}
+
 int main()
 {
     otInstance *instance = nullptr;

src/posix/platform/system.cpp

@@ -55,6 +55,7 @@
 #include "posix/platform/udp.hpp"
 
 otInstance *gInstance = nullptr;
+bool        gDryRun   = false;
 
 #if OPENTHREAD_CONFIG_PLATFORM_NETIF_ENABLE || OPENTHREAD_CONFIG_BACKBONE_ROUTER_ENABLE
 static void processStateChange(otChangedFlags aFlags, void *aContext)
@@ -122,6 +123,10 @@ void platformInit(otPlatformConfig *aPlatformConfig)
 {
     platformAlarmInit(aPlatformConfig->mSpeedUpFactor, aPlatformConfig->mRealTimeSignal);
     platformRadioInit(get802154RadioUrl(aPlatformConfig));
+
+    // For Dry-Run option, only init the radio.
+    VerifyOrExit(!aPlatformConfig->mDryRun);
+
 #if OPENTHREAD_CONFIG_RADIO_LINK_TREL_ENABLE
     platformTrelInit(getTrelRadioUrl(aPlatformConfig));
 #endif
@@ -148,6 +153,9 @@ void platformInit(otPlatformConfig *aPlatformConfig)
     ot::Posix::Udp::Get().Init(aPlatformConfig->mInterfaceName);
 #endif
 #endif
+
+exit:
+    return;
 }
 
 void platformSetUp(void)
@@ -183,6 +191,7 @@ otInstance *otSysInit(otPlatformConfig *aPlatformConfig)
 
     platformInit(aPlatformConfig);
 
+    gDryRun   = aPlatformConfig->mDryRun;
     gInstance = otInstanceInitSingle();
     OT_ASSERT(gInstance != nullptr);
 
@@ -377,3 +386,8 @@ void otPlatOtnsStatus(const char *aStatus)
 }
 
 #endif
+
+bool IsSystemDryRun(void)
+{
+    return gDryRun;
+}

src/posix/platform/system.hpp

@@ -0,0 +1,41 @@
+/*
+ *  Copyright (c) 2021, 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.
+ */
+
+/**
+ * @file
+ * @brief
+ *   This file includes posix-specific system methods.
+ */
+
+/*
+ * This method returns if the system will run in dry-run mode.
+ *
+ * @returns  If the system runs in dry-run mode.
+ *
+ */
+bool IsSystemDryRun(void);