glib: add compatibility interface for g_get_monotonic_time()

This patch fixes compilation errors when building against glib <2.28.0
due to the missing g_get_monotonic_time() function.

The compilation error in tests/libqos/virtio.c was introduced in commit
7055626 ("libqos: use microseconds
instead of iterations for virtio timeout").

Add a simple g_get_monotonic_time() implementation to glib-compat.h
based on code from vhost-user-test.c.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
[Igor: add G_TIME_SPAN_SECOND, include glib-compat.h in libqtest.h]
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

include/glib-compat.h

@@ -18,6 +18,11 @@
 
 #include <glib.h>
 
+/* GLIB version compatibility flags */
+#if !GLIB_CHECK_VERSION(2, 26, 0)
+#define G_TIME_SPAN_SECOND              (G_GINT64_CONSTANT(1000000))
+#endif
+
 #if !GLIB_CHECK_VERSION(2, 14, 0)
 static inline guint g_timeout_add_seconds(guint interval, GSourceFunc function,
                                           gpointer data)
@@ -26,6 +31,20 @@ static inline guint g_timeout_add_seconds(guint interval, GSourceFunc function,
 }
 #endif
 
+#if !GLIB_CHECK_VERSION(2, 28, 0)
+static inline gint64 g_get_monotonic_time(void)
+{
+    /* g_get_monotonic_time() is best-effort so we can use the wall clock as a
+     * fallback.
+     */
+
+    GTimeVal time;
+    g_get_current_time(&time);
+
+    return time.tv_sec * G_TIME_SPAN_SECOND + time.tv_usec;
+}
+#endif
+
 #ifdef _WIN32
 /*
  * g_poll has a problem on Windows when using

tests/libqtest.h

@@ -23,6 +23,7 @@
 #include <stdarg.h>
 #include <sys/types.h>
 #include "qapi/qmp/qdict.h"
+#include "glib-compat.h"
 
 typedef struct QTestState QTestState;
 

tests/vhost-user-test.c

@@ -21,15 +21,6 @@
 #include <sys/vfs.h>
 #include <qemu/sockets.h>
 
-/* GLIB version compatibility flags */
-#if !GLIB_CHECK_VERSION(2, 26, 0)
-#define G_TIME_SPAN_SECOND              (G_GINT64_CONSTANT(1000000))
-#endif
-
-#if GLIB_CHECK_VERSION(2, 28, 0)
-#define HAVE_MONOTONIC_TIME
-#endif
-
 #if GLIB_CHECK_VERSION(2, 32, 0)
 #define HAVE_MUTEX_INIT
 #define HAVE_COND_INIT
@@ -116,18 +107,6 @@ static VhostUserMemory memory;
 static GMutex *data_mutex;
 static GCond *data_cond;
 
-static gint64 _get_time(void)
-{
-#ifdef HAVE_MONOTONIC_TIME
-    return g_get_monotonic_time();
-#else
-    GTimeVal time;
-    g_get_current_time(&time);
-
-    return time.tv_sec * G_TIME_SPAN_SECOND + time.tv_usec;
-#endif
-}
-
 static GMutex *_mutex_new(void)
 {
     GMutex *mutex;
@@ -210,7 +189,7 @@ static void read_guest_mem(void)
 
     g_mutex_lock(data_mutex);
 
-    end_time = _get_time() + 5 * G_TIME_SPAN_SECOND;
+    end_time = g_get_monotonic_time() + 5 * G_TIME_SPAN_SECOND;
     while (!fds_num) {
         if (!_cond_wait_until(data_cond, data_mutex, end_time)) {
             /* timeout has passed */