From ced585c83b27deca427c606a34dd3eaa6b96d82b Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Tue, 17 Mar 2015 20:25:57 +0100 Subject: [PATCH] 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 Cc: Jiri Pirko Cc: Alexei Starovoitov Cc: Jamal Hadi Salim Acked-by: Jiri Pirko Signed-off-by: David S. Miller --- net/sched/act_bpf.c | 36 ++++++++++++++++++++++++++++-------- 1 file changed, 28 insertions(+), 8 deletions(-) diff --git a/net/sched/act_bpf.c b/net/sched/act_bpf.c index 82c5d7fc1988..5f6288fa3f12 100644 --- a/net/sched/act_bpf.c +++ b/net/sched/act_bpf.c @@ -25,21 +25,41 @@ static int tcf_bpf(struct sk_buff *skb, const struct tc_action *a, 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);