net_sched: make cls_ops->change and cls_ops->delete optional

Some schedulers don't support creating, changing or deleting classes.
Make the respective callbacks optionally and consistently return
-EOPNOTSUPP for unsupported operations, instead of currently either
-EOPNOTSUPP, -ENOSYS or no error.

In case of sch_prio and sch_multiq, the removed operations additionally
checked for an invalid class. This is not necessary since the class
argument can only orginate from ->get() or in case of ->change is 0
for creation of new classes, in which case ->change() incorrectly
returned -ENOENT.

As a side-effect, this patch fixes a possible (root-only) NULL pointer
function call in sch_ingress, which didn't implement a so far mandatory
->delete() operation.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 2 deletions

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index bef2d645a36..166fcca86e7 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -1417,7 +1417,9 @@ static int tc_ctl_tclass(struct sk_buff *skb, struct nlmsghdr *n, void *arg)
                                 goto out;
                         break;
                 case RTM_DELTCLASS:
-                        err = cops->delete(q, cl);
+                        err = -EOPNOTSUPP;
+                        if (cops->delete)
+                                err = cops->delete(q, cl);
                         if (err == 0)
                                 tclass_notify(skb, n, q, cl, RTM_DELTCLASS);
                         goto out;
@@ -1431,7 +1433,9 @@ static int tc_ctl_tclass(struct sk_buff *skb, struct nlmsghdr *n, void *arg)
         }
 
         new_cl = cl;
-        err = cops->change(q, clid, pid, tca, &new_cl);
+        err = -EOPNOTSUPP;
+        if (cops->change)
+                err = cops->change(q, clid, pid, tca, &new_cl);
         if (err == 0)
                 tclass_notify(skb, n, q, new_cl, RTM_NEWTCLASS);