Kernel: Add getrusage() syscall

Only the two timeval fields are maintained, as required by the POSIX
standard.

Kernel/Syscalls/resource.cpp

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2022, Lucas Chollet <lucas.chollet@free.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Process.h>
+
+namespace Kernel {
+
+ErrorOr<FlatPtr> Process::sys$getrusage(int who, Userspace<rusage*> user_usage)
+{
+    VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this)
+
+    rusage usage {};
+
+    auto const ticks_per_second = TimeManagement::the().ticks_per_second();
+
+    switch (who) {
+    case RUSAGE_SELF:
+        usage.ru_utime = Time::from_ticks(m_ticks_in_user, ticks_per_second).to_timeval();
+        usage.ru_stime = Time::from_ticks(m_ticks_in_kernel, ticks_per_second).to_timeval();
+        break;
+    case RUSAGE_CHILDREN:
+        usage.ru_utime = Time::from_ticks(m_ticks_in_user_for_dead_children, ticks_per_second).to_timeval();
+        usage.ru_stime = Time::from_ticks(m_ticks_in_kernel_for_dead_children, ticks_per_second).to_timeval();
+        break;
+    default:
+        return EINVAL;
+    }
+
+    TRY(copy_to_user(user_usage, &usage));
+
+    return 0;
+}
+
+}