act_bpf: allow non-default TC_ACT opcodes as BPF exec outcome
Revisiting commit d23b8ad8ab23 ("tc: add BPF based action") with regards
to eBPF support, I was thinking that it might be better to improve
return semantics from a BPF program invoked through BPF_PROG_RUN().
Currently, in case filter_res is 0, we overwrite the default action
opcode with TC_ACT_SHOT. A default action opcode configured through tc's
m_bpf can be: TC_ACT_RECLASSIFY, TC_ACT_PIPE, TC_ACT_SHOT, TC_ACT_UNSPEC,
TC_ACT_OK.
In cls_bpf, we have the possibility to overwrite the default class
associated with the classifier in case filter_res is _not_ 0xffffffff
(-1).
That allows us to fold multiple [e]BPF programs into a single one, where
they would otherwise need to be defined as a separate classifier with
its own classid, needlessly redoing parsing work, etc.
Similarly, we could do better in act_bpf: Since above TC_ACT* opcodes
are exported to UAPI anyway, we reuse them for return-code-to-tc-opcode
mapping, where we would allow above possibilities. Thus, like in cls_bpf,
a filter_res of 0xffffffff (-1) means that the configured _default_ action
is used. Any unkown return code from the BPF program would fail in
tcf_bpf() with TC_ACT_UNSPEC.
Should we one day want to make use of TC_ACT_STOLEN or TC_ACT_QUEUED,
which both have the same semantics, we have the option to either use
that as a default action (filter_res of 0xffffffff) or non-default BPF
return code.
All that will allow us to transparently use tcf_bpf() for both BPF
flavours.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jiri Pirko <jiri@resnulli.us>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Acked-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/act_bpf.c b/net/sched/act_bpf.c
index 82c5d7f..5f6288f 100644
--- a/net/sched/act_bpf.c
+++ b/net/sched/act_bpf.c
@@ -25,21 +25,41 @@
struct tcf_result *res)
{
struct tcf_bpf *b = a->priv;
- int action;
- int filter_res;
+ int action, filter_res;
spin_lock(&b->tcf_lock);
+
b->tcf_tm.lastuse = jiffies;
bstats_update(&b->tcf_bstats, skb);
- action = b->tcf_action;
filter_res = BPF_PROG_RUN(b->filter, skb);
- if (filter_res == 0) {
- /* Return code 0 from the BPF program
- * is being interpreted as a drop here.
- */
- action = TC_ACT_SHOT;
+
+ /* A BPF program may overwrite the default action opcode.
+ * Similarly as in cls_bpf, if filter_res == -1 we use the
+ * default action specified from tc.
+ *
+ * In case a different well-known TC_ACT opcode has been
+ * returned, it will overwrite the default one.
+ *
+ * For everything else that is unkown, TC_ACT_UNSPEC is
+ * returned.
+ */
+ switch (filter_res) {
+ case TC_ACT_PIPE:
+ case TC_ACT_RECLASSIFY:
+ case TC_ACT_OK:
+ action = filter_res;
+ break;
+ case TC_ACT_SHOT:
+ action = filter_res;
b->tcf_qstats.drops++;
+ break;
+ case TC_ACT_UNSPEC:
+ action = b->tcf_action;
+ break;
+ default:
+ action = TC_ACT_UNSPEC;
+ break;
}
spin_unlock(&b->tcf_lock);
