net/sched: mqprio: simplify handling of nlattr portion of TCA_OPTIONS

In commit 4e8b86c062 ("mqprio: Introduce new hardware offload mode and
shaper in mqprio"), the TCA_OPTIONS format of mqprio was extended to
contain a fixed portion (of size NLA_ALIGN(sizeof struct tc_mqprio_qopt))
and a variable portion of other nlattrs (in the TCA_MQPRIO_* type space)
following immediately afterwards.

In commit feb2cf3dcf ("net/sched: mqprio: refactor nlattr parsing to a
separate function"), we've moved the nlattr handling to a smaller
function, but yet, a small parse_attr() still remains, and the larger
mqprio_parse_nlattr() still does not have access to the beginning, and
the length, of the TCA_OPTIONS region containing these other nlattrs.

In a future change, the mqprio qdisc will need to iterate through this
nlattr region to discover other attributes, so eliminate parse_attr()
and add 2 variables in mqprio_parse_nlattr() which hold the beginning
and the length of the nlattr range.

We avoid the need to memset when nlattr_opt_len has insufficient length
by pre-initializing the table "tb".

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Ferenc Fejes <fejes@inf.elte.hu>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/sched/sch_mqprio.c

@@ -146,32 +146,26 @@ static const struct nla_policy mqprio_policy[TCA_MQPRIO_MAX + 1] = {
 	[TCA_MQPRIO_MAX_RATE64]	= { .type = NLA_NESTED },
 };
 
-static int parse_attr(struct nlattr *tb[], int maxtype, struct nlattr *nla,
-		      const struct nla_policy *policy, int len)
-{
-	int nested_len = nla_len(nla) - NLA_ALIGN(len);
-
-	if (nested_len >= nla_attr_size(0))
-		return nla_parse_deprecated(tb, maxtype,
-					    nla_data(nla) + NLA_ALIGN(len),
-					    nested_len, policy, NULL);
-
-	memset(tb, 0, sizeof(struct nlattr *) * (maxtype + 1));
-	return 0;
-}
-
+/* Parse the other netlink attributes that represent the payload of
+ * TCA_OPTIONS, which are appended right after struct tc_mqprio_qopt.
+ */
 static int mqprio_parse_nlattr(struct Qdisc *sch, struct tc_mqprio_qopt *qopt,
 			       struct nlattr *opt)
 {
+	struct nlattr *nlattr_opt = nla_data(opt) + NLA_ALIGN(sizeof(*qopt));
+	int nlattr_opt_len = nla_len(opt) - NLA_ALIGN(sizeof(*qopt));
 	struct mqprio_sched *priv = qdisc_priv(sch);
-	struct nlattr *tb[TCA_MQPRIO_MAX + 1];
+	struct nlattr *tb[TCA_MQPRIO_MAX + 1] = {};
 	struct nlattr *attr;
 	int i, rem, err;
 
-	err = parse_attr(tb, TCA_MQPRIO_MAX, opt, mqprio_policy,
-			 sizeof(*qopt));
-	if (err < 0)
-		return err;
+	if (nlattr_opt_len >= nla_attr_size(0)) {
+		err = nla_parse_deprecated(tb, TCA_MQPRIO_MAX, nlattr_opt,
+					   nlattr_opt_len, mqprio_policy,
+					   NULL);
+		if (err < 0)
+			return err;
+	}
 
 	if (!qopt->hw)
 		return -EINVAL;