lx_emul: allow setup of the persistent clock

This commit adds support to initialize the timekeeping for
the Linux subsystem with the value from the RTC.

Only the seconds part of timespec64 is supported.

Issue genodelabs/genode#4957

repos/dde_linux/lib/import/import-lx_emul_common.inc

@@ -40,6 +40,7 @@ SRC_C   += lx_emul/shadow/mm/slab_common.c
 SRC_C   += lx_emul/shadow/mm/slub.c
 SRC_C   += lx_emul/shadow/mm/vmstat.c
 SRC_C   += lx_emul/start.c
+SRC_C   += lx_emul/time_initial.c
 SRC_C   += lx_emul/virt_to_page.c
 
 SRC_CC  += lx_kit/console.cc

repos/dde_linux/src/include/lx_emul/time.h

@@ -30,6 +30,8 @@ void lx_emul_time_handle(void);
 
 void lx_emul_time_update_jiffies(void);
 
+void lx_emul_time_initial(unsigned long long);
+
 #ifdef __cplusplus
 }
 #endif

repos/dde_linux/src/lib/lx_emul/time_initial.c

@@ -0,0 +1,29 @@
+/*
+ * \brief  Lx_emul initial time (persistent clock)
+ * \author Pirmin Duss
+ * \date   2023-10-02
+ */
+
+/*
+ * Copyright (C) 2023 Genode Labs GmbH
+ * Copyright (C) 2023 gapfruit AG
+ *
+ * This file is distributed under the terms of the GNU General Public License
+ * version 2.
+ */
+
+
+#include <linux/time.h>
+
+static unsigned long long genode_initial_ts_sec = 0;
+
+void lx_emul_time_initial(unsigned long long seconds)
+{
+	genode_initial_ts_sec = seconds;
+}
+
+void read_persistent_clock64(struct timespec64 *ts)
+{
+	ts->tv_sec  = genode_initial_ts_sec;
+	ts->tv_nsec = 0;
+}