[disk_io_stats_diff] Implement method

README.mkdn

@@ -83,6 +83,7 @@ Here is a list of all exceptions in the `Statgrab` namespace:
 - `cpu_stats_diff`
 - `cpu_percents`
 - `disk_io_stats`
+- `disk_io_stats_diff`
 
 Somewhat relevant information is available for every method
 supplied with libstatgrab as manual pages:

statgrab.c

@@ -259,6 +259,33 @@ static VALUE statgrab_disk_io_stats(VALUE self) {
   return arr;
 }
 
+static VALUE statgrab_disk_io_stats_diff(VALUE self) {
+  int entries, i;
+  sg_disk_io_stats *stats;
+  VALUE arr, info;
+
+  stats = sg_get_disk_io_stats_diff(&entries);
+  if(stats==NULL)
+    statgrab_handle_error();
+
+  arr = rb_ary_new();
+  for(i = 0; i < entries; i++) {
+    info = rb_hash_new();
+    rb_hash_aset(info, ID2SYM(rb_intern("disk_name")), rb_str_new2(stats[i].disk_name));
+    rb_hash_aset(info, ID2SYM(rb_intern("read_bytes")), INT2NUM(stats[i].read_bytes));
+    rb_hash_aset(info, ID2SYM(rb_intern("write_bytes")), INT2NUM(stats[i].write_bytes));
+    rb_hash_aset(info, ID2SYM(rb_intern("systime")), INT2NUM(stats[i].systime));
+
+    VALUE time_now;
+    time_now = rb_funcall(rb_cTime, rb_intern("now"), 0);
+    rb_hash_aset(info, ID2SYM(rb_intern("last_call")), rb_funcall(time_now, rb_intern("-"), 1, INT2NUM(stats[i].systime)));
+
+    rb_ary_push(arr, info);
+  }
+
+  return arr;
+}
+
 void Init_statgrab() {
   cStatgrab = rb_define_class("Statgrab", rb_cObject);
   eStatgrabException = rb_define_class_under(cStatgrab, "Exception", rb_eException);
@@ -306,4 +333,5 @@ void Init_statgrab() {
   rb_define_method(cStatgrab, "cpu_stats_diff", statgrab_cpu_stats_diff, 0);
   rb_define_method(cStatgrab, "cpu_percents", statgrab_cpu_percents, 0);
   rb_define_method(cStatgrab, "disk_io_stats", statgrab_disk_io_stats, 0);
+  rb_define_method(cStatgrab, "disk_io_stats_diff", statgrab_disk_io_stats_diff, 0);
 }