swap plugin: Make SwapCached optional under Linux.

OpenVZ doesn't provide the line, which caused swap collection to be
skipped entirely on these systems. Instead, "cached" should simply be
ignored, as it is on other systems. Thanks to @zerkms for reporting this
problem!

Fixes: #733

diff --git a/src/swap.c b/src/swap.c
index 508f9d54cccbc04bb6fe05ce696bda18ad1a9350..0642afac78d82792318f40a57696cfe862d13ed2 100644 (file)
--- a/src/swap.c
+++ b/src/swap.c
@@ -295,11 +295,10 @@ static int swap_read_combined (void) /* {{{ */
        FILE *fh;
        char buffer[1024];
 
-       uint8_t have_data = 0;
-       gauge_t swap_used   = 0.0;
-       gauge_t swap_cached = 0.0;
-       gauge_t swap_free   = 0.0;
-       gauge_t swap_total  = 0.0;
+       gauge_t swap_used   = NAN;
+       gauge_t swap_cached = NAN;
+       gauge_t swap_free   = NAN;
+       gauge_t swap_total  = NAN;
 
        fh = fopen ("/proc/meminfo", "r");
        if (fh == NULL)
@@ -320,35 +319,30 @@ static int swap_read_combined (void) /* {{{ */
                        continue;
 
                if (strcasecmp (fields[0], "SwapTotal:") == 0)
-               {
-                       swap_total = strtod (fields[1], /* endptr = */ NULL);
-                       have_data |= 0x01;
-               }
+                       strtogauge (fields[1], &swap_total);
                else if (strcasecmp (fields[0], "SwapFree:") == 0)
-               {
-                       swap_free = strtod (fields[1], /* endptr = */ NULL);
-                       have_data |= 0x02;
-               }
+                       strtogauge (fields[1], &swap_free);
                else if (strcasecmp (fields[0], "SwapCached:") == 0)
-               {
-                       swap_cached = strtod (fields[1], /* endptr = */ NULL);
-                       have_data |= 0x04;
-               }
+                       strtogauge (fields[1], &swap_cached);
        }
 
        fclose (fh);
 
-       if (have_data != 0x07)
+       if (isnan (swap_total) || isnan (swap_free))
                return (ENOENT);
 
-       if (isnan (swap_total)
-                       || (swap_total <= 0.0)
-                       || ((swap_free + swap_cached) > swap_total))
-               return (EINVAL);
+       /* Some systems, OpenVZ for example, don't provide SwapCached. */
+       if (isnan (swap_cached))
+               swap_used = swap_total - swap_free;
+       else
+               swap_used = swap_total - (swap_free + swap_cached);
+       assert (!isnan (swap_used));
 
-       swap_used = swap_total - (swap_free + swap_cached);
+       if (swap_used < 0.0)
+               return (EINVAL);
 
-       swap_submit_usage (NULL, swap_used, swap_free, "cached", swap_cached);
+       swap_submit_usage (NULL, swap_used, swap_free,
+                       isnan (swap_cached) ? NULL : "cached", swap_cached);
        return (0);
 } /* }}} int swap_read_combined */