zdb: include cloned blocks in block statistics

This gives `zdb -b` support for clone blocks.

Previously, it didn't know what clones were, so would count their space
allocation multiple times and then report leaked space (or, in debug,
would assert trying to claim blocks a second time).

This commit fixes those bugs, and reports the number of clones and the
space "used" (saved) by them.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Kay Pedersen <mail@mkwg.de>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Sponsored-By: OpenDrives Inc.
Sponsored-By: Klara Inc.
Closes #15123

module/zfs/brt.c

@@ -1544,6 +1544,37 @@ out:
 	return (B_FALSE);
 }
 
+uint64_t
+brt_entry_get_refcount(spa_t *spa, const blkptr_t *bp)
+{
+	brt_t *brt = spa->spa_brt;
+	brt_vdev_t *brtvd;
+	brt_entry_t bre_search, *bre;
+	uint64_t vdevid, refcnt;
+	int error;
+
+	brt_entry_fill(bp, &bre_search, &vdevid);
+
+	brt_rlock(brt);
+
+	brtvd = brt_vdev(brt, vdevid);
+	ASSERT(brtvd != NULL);
+
+	bre = avl_find(&brtvd->bv_tree, &bre_search, NULL);
+	if (bre == NULL) {
+		error = brt_entry_lookup(brt, brtvd, &bre_search);
+		ASSERT(error == 0 || error == ENOENT);
+		if (error == ENOENT)
+			refcnt = 0;
+		else
+			refcnt = bre_search.bre_refcount;
+	} else
+		refcnt = bre->bre_refcount;
+
+	brt_unlock(brt);
+	return (refcnt);
+}
+
 static void
 brt_prefetch(brt_t *brt, const blkptr_t *bp)
 {