check_disk increase alert precision (#1989)

* check_disk increase alert precision

Free disk percentage value was rounded to a full integer meaning it alerted about ~1% percent too early. This is about 10GB on a 1TB disk.
The warning and critical thresholds already support float values, so just the percentage calculation needs to be improved.

old:

    ./check_disk -w 35% -c 20% -p / -f -vvv
    Thresholds(pct) for / warn: 35.000000 crit 20.000000
    calling stat on /
    For /, used_pct=65 free_pct=35 used_units=286451 free_units=156651 total_units=443102 used_inodes_pct=11 free_inodes_pct=89 fsp.fsu_blocksize=4096 mult=1048576
    Freespace_units result=0
    Freespace% result=1
    Usedspace_units result=0
    Usedspace_percent result=0
    Usedinodes_percent result=0
    Freeinodes_percent result=0
    DISK WARNING - free space: WARNING [ / 156651MiB (35% inode=89%)];| /=300365643776B;302006979788;371700898201;0;464626122752

new:

    ./check_disk -w 35% -c 20% -p / -f -vvv
    Thresholds(pct) for / warn: 35.000000 crit 20.000000
    calling stat on /
    For /, used_pct=64.649722 free_pct=35.350278 used_units=286464 free_units=156637 total_units=443102 used_inodes_pct=10.016183 free_inodes_pct=89.983817 fsp.fsu_blocksize=4096 mult=1048576
    Freespace_units result=0
    Freespace% result=0
    Usedspace_units result=0
    Usedspace_percent result=0
    Usedinodes_percent result=0
    Freeinodes_percent result=0
    DISK OK - free space: / 156637MiB (35.4% inode=90%);| /=300379275264B;302006979788;371700898201;0;464626122752

* check_disk: adjust test case to support float precision

2 files changed, 7 insertions, 23 deletions

diff --git a/plugins/check_disk.c b/plugins/check_disk.c
index c6bba24..0d84ecd 100644
--- a/plugins/check_disk.c
+++ b/plugins/check_disk.c
@@ -46,7 +46,7 @@ const char *email = "devel@monitoring-plugins.org";
 #include <stdarg.h>
 #include "fsusage.h"
 #include "mountlist.h"
-#include "intprops.h"    /* necessary for TYPE_MAXIMUM */
+#include <float.h>
 #if HAVE_LIMITS_H
 # include <limits.h>
 #endif
@@ -325,7 +325,7 @@ main (int argc, char **argv)
       get_stats (path, &fsp);
 
       if (verbose >= 3) {
-        printf ("For %s, used_pct=%g free_pct=%g used_units=%lu free_units=%lu total_units=%lu used_inodes_pct=%g free_inodes_pct=%g fsp.fsu_blocksize=%lu mult=%lu\n",
+        printf ("For %s, used_pct=%f free_pct=%f used_units=%lu free_units=%lu total_units=%lu used_inodes_pct=%f free_inodes_pct=%f fsp.fsu_blocksize=%lu mult=%lu\n",
                 me->me_mountdir,
                 path->dused_pct,
                 path->dfree_pct,
@@ -431,7 +431,7 @@ main (int argc, char **argv)
           } else {
                   xasprintf(&flag_header, "");
           }
-          xasprintf (&output, "%s%s %s %llu%s (%.0f%%",
+          xasprintf (&output, "%s%s %s %llu%s (%.1f%%",
                           output, flag_header,
                           (!strcmp(me->me_mountdir, "none") || display_mntp) ? me->me_devname : me->me_mountdir,
                           path->dfree_units,
@@ -461,24 +461,8 @@ main (int argc, char **argv)
 
 double calculate_percent(uintmax_t value, uintmax_t total) {
   double pct = -1;
-  /* I don't understand the below, but it is taken from coreutils' df */
-  /* Seems to be calculating pct, in the best possible way */
-  if (value <= TYPE_MAXIMUM(uintmax_t) / 100
-    && total != 0) {
-    uintmax_t u100 = value * 100;
-    pct = u100 / total + (u100 % total != 0);
-  } else {
-    /* Possible rounding errors - see coreutils' df for more explanation */
-    double u = value;
-    double t = total;
-    if (t) {
-      long int lipct = pct = u * 100 / t;
-      double ipct = lipct;
-
-      /* Like 'pct = ceil (dpct);', but without ceil - from coreutils again */
-      if (ipct - 1 < pct && pct <= ipct + 1)
-        pct = ipct + (ipct < pct);
-    }
+  if(value <= DBL_MAX && total != 0) {
+    pct = (double)value / total * 100.0;
   }
   return pct;
 }
@@ -1130,7 +1114,7 @@ get_stats (struct parameter_list *p, struct fs_usage *fsp) {
   }
   /* finally calculate percentages for either plain FS or summed up group */
   p->dused_pct = calculate_percent( p->used, p->used + p->available );    /* used + available can never be > uintmax */
-  p->dfree_pct = 100 - p->dused_pct;
+  p->dfree_pct = 100.0 - p->dused_pct;
   p->dused_inodes_percent = calculate_percent(p->inodes_total - p->inodes_free, p->inodes_total);
   p->dfree_inodes_percent = 100 - p->dused_inodes_percent;
 
diff --git a/plugins/t/check_disk.t b/plugins/t/check_disk.t
index bf8dd36..e0dd70e 100644
--- a/plugins/t/check_disk.t
+++ b/plugins/t/check_disk.t
@@ -44,7 +44,7 @@ my @perf_data = sort(split(/ /, $result->perf_output));
 # Calculate avg_free free on mountpoint1 and mountpoint2
 # because if you check in the middle, you should get different errors
 $_ = $result->output;
-my ($free_on_mp1, $free_on_mp2) = (m/\((\d+)%.*\((\d+)%/);
+my ($free_on_mp1, $free_on_mp2) = (m/\((\d+\.\d+)%.*\((\d+\.\d+)%/);
 die "Cannot parse output: $_" unless ($free_on_mp1 && $free_on_mp2);
 my $avg_free = ceil(($free_on_mp1+$free_on_mp2)/2);
 my ($more_free, $less_free);