Display uptime for processes (#6654)

* Get process uptime

* Calculate target uptime

* Update charts

* Show collected data

* Fix chart names

* Update the documentation

* Fix a flag value

* Add an explanation note for the 'carried over uptime' chart

* Move the functions for getting uptime to libnetdata

* Rename the function for geting uptime

* Remove redundant code

* Fix starttime calculation

* More accurate definition for the carried over uptime

* fix group starttime calculation

* Fix typo

2 files changed, 67 insertions, 0 deletions

diff --git a/libnetdata/clocks/clocks.c b/libnetdata/clocks/clocks.c
index f7d2171780..161225a9b6 100644
--- a/libnetdata/clocks/clocks.c
+++ b/libnetdata/clocks/clocks.c
@@ -210,3 +210,68 @@ int sleep_usec(usec_t usec) {
     return ret;
 #endif
 }
+
+static inline collected_number uptime_from_boottime(void) {
+#ifdef CLOCK_BOOTTIME_IS_AVAILABLE
+    return now_boottime_usec() / 1000;
+#else
+    error("uptime cannot be read from CLOCK_BOOTTIME on this system.");
+    return 0;
+#endif
+}
+
+static procfile *read_proc_uptime_ff = NULL;
+static inline collected_number read_proc_uptime(char *filename) {
+    if(unlikely(!read_proc_uptime_ff)) {
+        read_proc_uptime_ff = procfile_open(filename, " \t", PROCFILE_FLAG_DEFAULT);
+        if(unlikely(!read_proc_uptime_ff)) return 0;
+    }
+
+    read_proc_uptime_ff = procfile_readall(read_proc_uptime_ff);
+    if(unlikely(!read_proc_uptime_ff)) return 0;
+
+    if(unlikely(procfile_lines(read_proc_uptime_ff) < 1)) {
+        error("/proc/uptime has no lines.");
+        return 0;
+    }
+    if(unlikely(procfile_linewords(read_proc_uptime_ff, 0) < 1)) {
+        error("/proc/uptime has less than 1 word in it.");
+        return 0;
+    }
+
+    return (collected_number)(strtold(procfile_lineword(read_proc_uptime_ff, 0, 0), NULL) * 1000.0);
+}
+
+inline collected_number uptime_msec(char *filename){
+    static int use_boottime = -1;
+
+    if(unlikely(use_boottime == -1)) {
+        collected_number uptime_boottime = uptime_from_boottime();
+        collected_number uptime_proc     = read_proc_uptime(filename);
+
+        long long delta = (long long)uptime_boottime - (long long)uptime_proc;
+        if(delta < 0) delta = -delta;
+
+        if(delta <= 1000 && uptime_boottime != 0) {
+            procfile_close(read_proc_uptime_ff);
+            info("Using now_boottime_usec() for uptime (dt is %lld ms)", delta);
+            use_boottime = 1;
+        }
+        else if(uptime_proc != 0) {
+            info("Using /proc/uptime for uptime (dt is %lld ms)", delta);
+            use_boottime = 0;
+        }
+        else {
+            error("Cannot find any way to read uptime on this system.");
+            return 1;
+        }
+    }
+
+    collected_number uptime;
+    if(use_boottime)
+        uptime = uptime_from_boottime();
+    else
+        uptime = read_proc_uptime(filename);
+
+    return uptime;
+}
diff --git a/libnetdata/clocks/clocks.h b/libnetdata/clocks/clocks.h
index 47aa148c12..4af451d60a 100644
--- a/libnetdata/clocks/clocks.h
+++ b/libnetdata/clocks/clocks.h
@@ -136,4 +136,6 @@ extern int sleep_usec(usec_t usec);
  */
 void test_clock_boottime(void);
 
+extern collected_number uptime_msec(char *filename);
+
 #endif /* NETDATA_CLOCKS_H */