Linux: Auto-detecting clock adjustment mode

libuavcan_drivers/linux/include/uavcan_linux/clock.hpp

@@ -6,8 +6,12 @@
 
 #include <cassert>
 #include <ctime>
-#include <sys/time.h>
 #include <cstdint>
+
+#include <unistd.h>
+#include <sys/time.h>
+#include <sys/types.h>
+
 #include <uavcan/driver/system_clock.hpp>
 #include <uavcan_linux/exception.hpp>
 
@@ -56,8 +60,14 @@ class SystemClock : public uavcan::ISystemClock
         return adjtime(&tv, nullptr) == 0;
     }
 
+    static ClockAdjustmentMode detectPreferredClockAdjustmentMode()
+    {
+        const bool godmode = geteuid() == 0;
+        return godmode ? ClockAdjustmentMode::SystemWide : ClockAdjustmentMode::PerDriverPrivate;
+    }
+
 public:
-    SystemClock(ClockAdjustmentMode adj_mode = ClockAdjustmentMode::SystemWide)
+    SystemClock(ClockAdjustmentMode adj_mode = detectPreferredClockAdjustmentMode())
         : gradual_adj_limit_(uavcan::UtcDuration::fromMSec(4000))
         , adj_mode_(adj_mode)
         , step_adj_cnt_(0)

libuavcan_drivers/linux/test/test_clock.cpp

@@ -15,12 +15,36 @@ static std::string systime2str(const std::chrono::system_clock::time_point& tp)
 
 int main()
 {
+    uavcan_linux::SystemClock clock;
+
+    /*
+     * Auto-detected clock adjustment mode
+     */
+    std::cout << "Clock adjustment mode: ";
+    switch (clock.getAdjustmentMode())
+    {
+    case uavcan_linux::ClockAdjustmentMode::SystemWide:
+    {
+        std::cout << "SystemWide";
+        break;
+    }
+    case uavcan_linux::ClockAdjustmentMode::PerDriverPrivate:
+    {
+        std::cout << "PerDriverPrivate";
+        break;
+    }
+    default:
+        std::abort();
+    }
+    std::cout << std::endl;
+
+    /*
+     * Test adjustment
+     */
     double sec = 0;
     std::cout << "Enter system time adjustment in seconds (fractions allowed): " << std::endl;
     std::cin >> sec;
 
-    uavcan_linux::SystemClock clock;
-
     const auto before = std::chrono::system_clock::now();
     try
     {