Drop a non-zero totl key if it has no contributing xattrs.

The expected case is when the last xattr with a totl key is removed that
the count and value both reach zero. In case of a mismatch or corrupted
value, we have several different failure modes:

- count zero, value non-zero
- value zero, count non-zero
- both non-zero

The first case is the easiest to resolve, which is what this patch does
- it drops it and prints an error.

The other cases are more difficult and need a manual method to erase the
stale key, and one would have to scan the entire namespace to make sure
that the xattrs are indeed all removed.

Signed-off-by: Auke Kok <auke.kok@versity.com>

kmod/src/wkic.c

@@ -30,6 +30,7 @@
 #include "counters.h"
 #include "scoutfs_trace.h"
 #include "wkic.h"
+#include "msg.h"
 
 /*
  * This weaker item cache differs from the core item cache in item.c:
@@ -746,6 +747,16 @@ static void fill_page_items(struct super_block *sb, struct wkic_page *wpage, str
 				rb_erase(&witem->node, root);
 				kfree(witem);
 				continue;
+			} else if (tval->count == 0) {
+				/*
+				 * BUG: there are no contributing items but count != 0,
+				 * which shouldn't happen - we've gone off kilt.
+				 */
+				scoutfs_err(sb, "non-zero value for zero count totl "SK_FMT", dropping item",
+					    SK_ARG(&witem->key));
+				rb_erase(&witem->node, root);
+				kfree(witem);
+				continue;
 			}
 		}