mx_util: Add mx_clock_getboottime

Add function to return seconds from CLOCK_BOOTTIME. This clock is
strictly monotonic and can be used if values are not communicated to
other systems and are not kept accross reboots.

mx_util.c

@@ -10,7 +10,7 @@
 #include <unistd.h>
 
 #include <ctype.h>
-
+#include <time.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/vfs.h>
@@ -1305,3 +1305,12 @@ unsigned long mx_df(const char *path) {
     }
     return s.f_bavail*s.f_frsize;
 }
+
+time_t mx_clock_boottime() {
+    struct timespec ts;
+    int res = clock_gettime(CLOCK_BOOTTIME, &ts);
+    if (res != 0) {
+        perror("clock_gettime");
+    }
+    return (ts.tv_sec);
+}

mx_util.h

@@ -179,5 +179,5 @@ void _mx_sort_linked_list(void **list, int (*cmp)(void *o1,void *o2), void ** (*
 #define mx_sort_linked_list(list,cmp,getnextptr) _mx_sort_linked_list((void **)(list),(int (*)(void *,void *))(cmp),(void ** (*)(void *))(getnextptr)) 
 
 unsigned long mx_df(const char *path);
-
+time_t mx_clock_boottime();
 #endif