net: tc: improve qdisc error messages

The existing error message ("Invalid qdisc name") is confusing
because it suggests that there is no qdisc with the given name. In
fact, the name does refer to a valid qdisc, but it doesn't match
the kind of an existing qdisc being modified or replaced. The
new error message provides more detail to eliminate confusion.

Signed-off-by: John Ousterhout <ouster@cs.stanford.edu>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20250116195642.2794-1-ouster@cs.stanford.edu
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 300430b8c4d22f59f2b5a61bc9bb53ceb4825e1b..5d017c06a96fb31b962c8ed0f522d8bea84193d3 100644 (file)
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -1560,7 +1560,7 @@ static int tc_get_qdisc(struct sk_buff *skb, struct nlmsghdr *n,
        }
 
        if (tca[TCA_KIND] && nla_strcmp(tca[TCA_KIND], q->ops->id)) {
-               NL_SET_ERR_MSG(extack, "Invalid qdisc name");
+               NL_SET_ERR_MSG(extack, "Invalid qdisc name: must match existing qdisc");
                return -EINVAL;
        }
 
@@ -1670,7 +1670,7 @@ replay:
                                }
                                if (tca[TCA_KIND] &&
                                    nla_strcmp(tca[TCA_KIND], q->ops->id)) {
-                                       NL_SET_ERR_MSG(extack, "Invalid qdisc name");
+                                       NL_SET_ERR_MSG(extack, "Invalid qdisc name: must match existing qdisc");
                                        return -EINVAL;
                                }
                                if (q->flags & TCQ_F_INGRESS) {
@@ -1746,7 +1746,7 @@ replay:
                return -EEXIST;
        }
        if (tca[TCA_KIND] && nla_strcmp(tca[TCA_KIND], q->ops->id)) {
-               NL_SET_ERR_MSG(extack, "Invalid qdisc name");
+               NL_SET_ERR_MSG(extack, "Invalid qdisc name: must match existing qdisc");
                return -EINVAL;
        }
        err = qdisc_change(q, tca, extack);