rrdtool plugin: Use `-b' (begin) when creating rrd-files.

When receiving data from a host that has a clock that lacks behind the servers
clock, the newly created rrd-files had a timestamp that was ten seconds in the
past from the server's point of view. If the client was, for example, 10:00
minutes late, there would therefore be 9:50 minutes of invalid data which cause
warnings, empty graphs and overall missery. This commit changes this behavior
to not use the default `begin' time but set it explicitely based on the
client's time.

diff --git a/src/rrdtool.c b/src/rrdtool.c
index d20a814..820ccdc 100644 (file)
--- a/src/rrdtool.c
+++ b/src/rrdtool.c
@@ -283,7 +283,7 @@ static int ds_get (char ***ret, const data_set_t *ds)
        return (ds_num);
 }
 
-static int rrd_create_file (char *filename, const data_set_t *ds)
+static int rrd_create_file (char *filename, const data_set_t *ds, const value_list_t *vl)
 {
        char **argv;
        int argc;
@@ -293,6 +293,7 @@ static int rrd_create_file (char *filename, const data_set_t *ds)
        int ds_num;
        int i, j;
        char stepsize_str[16];
+       char begin_str[16];
        int status = 0;
 
        if (check_create_dir (filename))
@@ -310,7 +311,7 @@ static int rrd_create_file (char *filename, const data_set_t *ds)
                return (-1);
        }
 
-       argc = ds_num + rra_num + 4;
+       argc = ds_num + rra_num + 6;
 
        if ((argv = (char **) malloc (sizeof (char *) * (argc + 1))) == NULL)
        {
@@ -328,12 +329,23 @@ static int rrd_create_file (char *filename, const data_set_t *ds)
                return (-1);
        }
 
+       assert (vl->time > 10);
+       status = snprintf (begin_str, sizeof (begin_str),
+                       "%llu", (unsigned long long) (vl->time - 10));
+       if ((status < 1) || (status >= sizeof (begin_str)))
+       {
+               ERROR ("rrdtool plugin: snprintf failed.");
+               return (-1);
+       }
+
        argv[0] = "create";
        argv[1] = filename;
-       argv[2] = "-s";
-       argv[3] = stepsize_str;
+       argv[2] = "-b";
+       argv[3] = begin_str;
+       argv[4] = "-s";
+       argv[5] = stepsize_str;
 
-       j = 4;
+       j = 6;
        for (i = 0; i < ds_num; i++)
                argv[j++] = ds_def[i];
        for (i = 0; i < rra_num; i++)
@@ -650,7 +662,7 @@ static int rrd_write (const data_set_t *ds, const value_list_t *vl)
        {
                if (errno == ENOENT)
                {
-                       if (rrd_create_file (filename, ds))
+                       if (rrd_create_file (filename, ds, vl))
                                return (-1);
                }
                else