libkvm - Adjust new sysctl-based kvm_getswapinfo() code

* Make it adhere to the original API which populates a cumulative
  result at swap_ary[returned_index].

Submitted-by: Ilya Dryomov <idryomov@gmail.com>

diff --git a/lib/libkvm/kvm_getswapinfo.c b/lib/libkvm/kvm_getswapinfo.c
index b2558d1..51e3f75 100644 (file)
--- a/lib/libkvm/kvm_getswapinfo.c
+++ b/lib/libkvm/kvm_getswapinfo.c
@@ -486,11 +486,15 @@ kvm_getswapinfo_sysctl(kvm_t *kd, struct kvm_swap *swap_ary,
        size_t bytes = 0;
        size_t ksize;
        int ti;
+       int swi;
        int n;
        int i;
        char *xswbuf;
        struct xswdev *xsw;
 
+       if (swap_max < 1)
+               return(-1);
+
        if (sysctlbyname("vm.swap_info_array", NULL, &bytes, NULL, 0) < 0)
                return(-1);
        if (bytes == 0)
@@ -512,40 +516,62 @@ kvm_getswapinfo_sysctl(kvm_t *kd, struct kvm_swap *swap_ary,
        /*
         * Calculate size of xsw entry returned by kernel (it can be larger
         * than the one we have if there is a version mismatch).
-        *
-        * Then iterate the list looking for live swap devices.
         */
        ksize = ((struct xswdev *)xswbuf)->xsw_size;
        n = (int)(bytes / ksize);
 
-       for (i = ti = 0; i < n && ti < swap_max; ++i) {
+       /*
+        * Calculate the number of live swap devices and calculate
+        * the swap_ary[] index used for the cumulative result (swi)
+        */
+       for (i = swi = 0; i < n; ++i) {
                xsw = (void *)((char *)xswbuf + i * ksize);
-
                if ((xsw->xsw_flags & SW_FREED) == 0)
                        continue;
+               ++swi;
+       }
+       if (swi > swap_max)
+               swi = swap_max;
+
+       /*
+        * Accumulate results.  If the provided swap_ary[] is too
+        * small will only populate up to the available entries,
+        * but we always populate the cumulative results entry.
+        */
+       for (i = ti = 0; i < n; ++i) {
+               xsw = (void *)((char *)xswbuf + i * ksize);
 
-               swap_ary[ti].ksw_total = xsw->xsw_nblks;
-               swap_ary[ti].ksw_used = xsw->xsw_used;
-               swap_ary[ti].ksw_flags = xsw->xsw_flags;
+               if ((xsw->xsw_flags & SW_FREED) == 0)
+                       continue;
 
-               if (xsw->xsw_dev == NODEV) {
-                       snprintf(
-                           swap_ary[ti].ksw_devname,
-                           sizeof(swap_ary[ti].ksw_devname),
-                           "%s",
-                           "[NFS swap]"
-                       );
-               } else {
-                       snprintf(
-                           swap_ary[ti].ksw_devname,
-                           sizeof(swap_ary[ti].ksw_devname),
-                           "%s%s",
-                           ((flags & SWIF_DEV_PREFIX) ? _PATH_DEV : ""),
-                           devname(xsw->xsw_dev, S_IFCHR)
-                       );
+               swap_ary[swi].ksw_total += xsw->xsw_nblks;
+               swap_ary[swi].ksw_used += xsw->xsw_used;
+
+               if (ti < swap_max) {
+                       swap_ary[ti].ksw_total = xsw->xsw_nblks;
+                       swap_ary[ti].ksw_used = xsw->xsw_used;
+                       swap_ary[ti].ksw_flags = xsw->xsw_flags;
+
+                       if (xsw->xsw_dev == NODEV) {
+                               snprintf(
+                                   swap_ary[ti].ksw_devname,
+                                   sizeof(swap_ary[ti].ksw_devname),
+                                   "%s",
+                                   "[NFS swap]"
+                               );
+                       } else {
+                               snprintf(
+                                   swap_ary[ti].ksw_devname,
+                                   sizeof(swap_ary[ti].ksw_devname),
+                                   "%s%s",
+                                   ((flags & SWIF_DEV_PREFIX) ? _PATH_DEV : ""),
+                                   devname(xsw->xsw_dev, S_IFCHR)
+                               );
+                       }
+                       ++ti;
                }
-               ++ti;
        }
+
        free(xswbuf);
-       return(ti);
+       return(swi);
 }