crush: warn on do_rule failure

If we get an error code from crush_do_rule(), print an error to the
console.
Reviewed-by: Alex Elder <elder@inktank.com>
Signed-off-by: Sage Weil <sage@inktank.com>

net/ceph/osdmap.c

@@ -1027,7 +1027,7 @@ static int *calc_pg_raw(struct ceph_osdmap *osdmap, struct ceph_pg pgid,
 	struct ceph_pg_mapping *pg;
 	struct ceph_pg_pool_info *pool;
 	int ruleno;
-	unsigned poolid, ps, pps, t;
+	unsigned poolid, ps, pps, t, r;
 
 	poolid = le32_to_cpu(pgid.pool);
 	ps = le16_to_cpu(pgid.ps);
@@ -1060,9 +1060,16 @@ static int *calc_pg_raw(struct ceph_osdmap *osdmap, struct ceph_pg pgid,
 			      le32_to_cpu(pool->v.pgp_num),
 			      pool->pgp_num_mask);
 	pps += poolid;
-	*num = crush_do_rule(osdmap->crush, ruleno, pps, osds,
-			     min_t(int, pool->v.size, *num),
-			     osdmap->osd_weight);
+	r = crush_do_rule(osdmap->crush, ruleno, pps, osds,
+			  min_t(int, pool->v.size, *num),
+			  osdmap->osd_weight);
+	if (r < 0) {
+		pr_err("error %d from crush rule: pool %d ruleset %d type %d"
+		       " size %d\n", r, poolid, pool->v.crush_ruleset,
+		       pool->v.type, pool->v.size);
+		return NULL;
+	}
+	*num = r;
 	return osds;
 }