genetlink: refactor the cmd <> policy mapping dump

The code at the top of ctrl_dumppolicy() dumps mappings between
ops and policies. It supports dumping both the entire family and
single op if dump is filtered. But both of those cases are handled
inside a loop, which makes the logic harder to follow and change.
Refactor to split the two cases more clearly.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netlink/genetlink.c

@@ -1319,7 +1319,6 @@ static int ctrl_dumppolicy(struct sk_buff *skb, struct netlink_callback *cb)
 	void *hdr;
 
 	if (!ctx->policies) {
-		while (ctx->opidx < genl_get_cmd_cnt(ctx->rt)) {
 		struct genl_ops op;
 
 		if (ctx->single_op) {
@@ -1327,14 +1326,18 @@ static int ctrl_dumppolicy(struct sk_buff *skb, struct netlink_callback *cb)
 
 			err = genl_get_cmd(ctx->op, ctx->rt, &op);
 			if (WARN_ON(err))
+				return err;
+
+			if (ctrl_dumppolicy_put_op(skb, cb, &op))
 				return skb->len;
 
-				/* break out of the loop after this one */
+			/* don't enter the loop below */
 			ctx->opidx = genl_get_cmd_cnt(ctx->rt);
-			} else {
-				genl_get_cmd_by_index(ctx->opidx, ctx->rt, &op);
 		}
 
+		while (ctx->opidx < genl_get_cmd_cnt(ctx->rt)) {
+			genl_get_cmd_by_index(ctx->opidx, ctx->rt, &op);
+
 			if (ctrl_dumppolicy_put_op(skb, cb, &op))
 				return skb->len;