Swap: improve performance on Linux

We can't do the same thing with memory because there is no `cachedram` in `struct sysinfo`

Author: CarterLi

src/detection/swap/swap_linux.c

@@ -1,34 +1,13 @@
 #include "swap.h"
 
-#include <stdlib.h>
-#include <string.h>
+#include <sys/sysinfo.h>
 
 void ffDetectSwap(FFMemoryStorage* swap)
 {
-    FILE* meminfo = fopen("/proc/meminfo", "r");
-    if(meminfo == NULL)
-    {
-        ffStrbufAppendS(&swap->error, "Failed to open /proc/meminfo");
-        return;
-    }
+    struct sysinfo info;
+    if(sysinfo(&info) != 0)
+        ffStrbufAppendS(&swap->error, "sysinfo() failed");
 
-    char* line = NULL;
-    size_t len = 0;
-
-    uint32_t swapTotal = 0,
-             swapFree = 0;
-
-    while (getline(&line, &len, meminfo) != EOF)
-    {
-        if(!sscanf(line, "SwapTotal: %u", &swapTotal))
-            sscanf(line, "SwapFree: %u", &swapFree);
-    }
-
-    if(line != NULL)
-        free(line);
-
-    fclose(meminfo);
-
-    swap->bytesTotal = swapTotal * (uint64_t) 1024;
-    swap->bytesUsed = (swapTotal - swapFree) * (uint64_t) 1024;
+    swap->bytesTotal = info.totalswap * (uint64_t) info.mem_unit;
+    swap->bytesUsed = (info.totalswap - info.freeswap) * (uint64_t) info.mem_unit;
 }