[PATCH net-next 3/4] net/sched: netem: replace pr_info with netlink extack error messages

Stephen Hemminger
2026-05-02T00:18:52Z

netem predates the netlink extended ack mechanism and uses pr_info()
to report configuration errors. These messages go to the kernel log
where the user running tc may never see them, and in unprivileged
user namespace contexts they can be used for log spam.

Replace pr_info() with NL_SET_ERR_MSG() and NL_SET_ERR_MSG_FMT()
which return error details to the caller via netlink. Thread the
extack pointer through parse_attr() and get_loss_clg(). Remove
the uninformative "netem: change failed" message from netem_init()
since the error is already propagated.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
net/sched/sch_netem.c | 26 ++++++++++++++------------
1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index 9ce75d9b8c54..116e96d79ddf 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -918,7 +918,8 @@ static void get_rate(struct netem_sched_data *q, const struct nlattr *attr)
q->cell_size_reciprocal = (struct reciprocal_value) { 0 };
}

-static int get_loss_clg(struct netem_sched_data *q, const struct nlattr *attr)
+static int get_loss_clg(struct netem_sched_data *q, const struct nlattr *attr,
+ struct netlink_ext_ack *extack)
{
const struct nlattr *la;
int rem;
@@ -931,7 +932,8 @@ static int get_loss_clg(struct netem_sched_data *q, const struct nlattr *attr)
const struct tc_netem_gimodel *gi = nla_data(la);

if (nla_len(la) < sizeof(struct tc_netem_gimodel)) {
- pr_info("netem: incorrect gi model size\n");
+ NL_SET_ERR_MSG(extack,
+ "netem: incorrect gi model size");
return -EINVAL;
}

@@ -950,7 +952,8 @@ static int get_loss_clg(struct netem_sched_data *q, const struct nlattr *attr)
const struct tc_netem_gemodel *ge = nla_data(la);

if (nla_len(la) < sizeof(struct tc_netem_gemodel)) {
- pr_info("netem: incorrect ge model size\n");
+ NL_SET_ERR_MSG(extack,
+ "netem: incorrect ge model size");
return -EINVAL;
}

@@ -964,7 +967,7 @@ static int get_loss_clg(struct netem_sched_data *q, const struct nlattr *attr)
}

default:
- pr_info("netem: unknown loss type %u\n", type);
+ NL_SET_ERR_MSG_FMT(extack, "netem: unknown loss type %u", type);
return -EINVAL;
}
}
@@ -987,12 +990,14 @@ static const struct nla_policy netem_policy[TCA_NETEM_MAX + 1] = {
};

static int parse_attr(struct nlattr *tb[], int maxtype, struct nlattr *nla,
- const struct nla_policy *policy, int len)
+ const struct nla_policy *policy, size_t len,
+ struct netlink_ext_ack *extack)
{
int nested_len = nla_len(nla) - NLA_ALIGN(len);

if (nested_len < 0) {
- pr_info("netem: invalid attributes len %d\n", nested_len);
+ NL_SET_ERR_MSG_FMT(extack, "netem: invalid attributes len %u < %zu",
+ nla_len(nla), NLA_ALIGN(len));
return -EINVAL;
}

@@ -1041,8 +1046,7 @@ static int check_netem_in_tree(struct Qdisc *sch, bool duplicates,
}

/* Parse netlink message to set options */
-static int netem_change(struct Qdisc *sch, struct nlattr *opt,
- struct netlink_ext_ack *extack)
+static int netem_change(struct Qdisc *sch, struct nlattr *opt, struct netlink_ext_ack *extack)
{
struct netem_sched_data *q = qdisc_priv(sch);
struct nlattr *tb[TCA_NETEM_MAX + 1];
@@ -1054,7 +1058,7 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,
int ret;

qopt = nla_data(opt);
- ret = parse_attr(tb, TCA_NETEM_MAX, opt, netem_policy, sizeof(*qopt));
+ ret = parse_attr(tb, TCA_NETEM_MAX, opt, netem_policy, sizeof(*qopt), extack);
if (ret < 0)
return ret;

@@ -1094,7 +1098,7 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,
old_loss_model = q->loss_model;

if (tb[TCA_NETEM_LOSS]) {
- ret = get_loss_clg(q, tb[TCA_NETEM_LOSS]);
+ ret = get_loss_clg(q, tb[TCA_NETEM_LOSS], extack);
if (ret) {
q->loss_model = old_loss_model;
q->clg = old_clg;
@@ -1190,8 +1194,6 @@ static int netem_init(struct Qdisc *sch, struct nlattr *opt,
prandom_seed_state(&q->prng.prng_state, q->prng.seed);

ret = netem_change(sch, opt, extack);
- if (ret)
- pr_info("netem: change failed\n");
return ret;
}

--
2.53.0