netdev - Re: [PATCH net] act_bpf: allow non-default TC

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Message-ID: <20150317222753.GA2169@nanopsycho.orion>
Date:	Tue, 17 Mar 2015 23:27:53 +0100
From:	Jiri Pirko <jiri@...nulli.us>
To:	Daniel Borkmann <daniel@...earbox.net>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	Alexei Starovoitov <ast@...mgrid.com>,
	Jamal Hadi Salim <jhs@...atatu.com>
Subject: Re: [PATCH net] act_bpf: allow non-default TC_ACT opcodes as BPF
 exec outcome

Tue, Mar 17, 2015 at 08:25:57PM CET, daniel@...earbox.net wrote:
>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@...earbox.net>
>Cc: Jiri Pirko <jiri@...nulli.us>
>Cc: Alexei Starovoitov <ast@...mgrid.com>
>Cc: Jamal Hadi Salim <jhs@...atatu.com>
>---
> Note, act_bpf has not been officially released with 4.0, so we can
> still address it.

Thanks for taking care of this Daniel

Acked-by: Jiri Pirko <jiri@...nulli.us>
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