netdev - Re: [PATCH iproute2 net-next] tc: flower: support matching flags

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Date:   Tue, 3 Jan 2017 13:54:34 +0200
From:   Paul Blakey <paulb@...lanox.com>
To:     Jiri Benc <jbenc@...hat.com>
CC:     <paulb@...lanox.com>, <netdev@...r.kernel.org>,
        Stephen Hemminger <stephen@...workplumber.org>,
        "David S. Miller" <davem@...emloft.net>,
        Hadar Hen Zion <hadarh@...lanox.com>,
        Or Gerlitz <ogerlitz@...lanox.com>,
        Roi Dayan <roid@...lanox.com>
Subject: Re: [PATCH iproute2 net-next] tc: flower: support matching flags

On 02/01/2017 20:55, Jiri Benc wrote:
> On Wed, 28 Dec 2016 15:06:49 +0200, Paul Blakey wrote:
>> Enhance flower to support matching on flags.
>>
>> The 1st flag allows to match on whether the packet is
>> an IP fragment.
>>
>> Example:
>>
>> 	# add a flower filter that will drop fragmented packets
>> 	# (bit 0 of control flags)
>> 	tc filter add dev ens4f0 protocol ip parent ffff: \
>> 		flower \
>> 		src_mac e4:1d:2d:fd:8b:01 \
>> 		dst_mac e4:1d:2d:fd:8b:02 \
>> 		indev ens4f0 \
>> 		matching_flags 0x1/0x1 \
>> 	action drop
> This is very poor API. First, how is the user supposed to know what
> those magic values in "matching_flags" mean? At the very least, it
> should be documented in the man page.
>
> Second, why "matching_flags"? That name suggests that those modify the
> way the matching is done (to illustrate my point, I'd expect things
> like "if the packet is too short, match this rule anyway" to be a
> "matching flag"). But this is not the case. What's wrong with plain
> "flags"? Or, if you want to be more specific, perhaps packet_flags?
>
> Third, all of this looks very wrong anyway. There should be separate
> keywords for individual flags. In this case, there should be an
> "ip_fragment" flag. The tc tool should be responsible for putting the
> flags together and creating the appropriate mask. The example would
> then be:
>
> 	tc filter add dev ens4f0 protocol ip parent ffff: \
> 		flower \
> 		src_mac e4:1d:2d:fd:8b:01 \
> 		dst_mac e4:1d:2d:fd:8b:02 \
> 		indev ens4f0 \
> 		ip_fragment yes\
> 	action drop
>
> I don't care whether it's "ip_fragment yes/no", "ip_fragment 1/0",
> "ip_fragment/noip_fragment" or similar. The important thing is it's a
> boolean flag; if specified, it's set to 0/1 and unmasked, if not
> specified, it's wildcarded.
>
> Stephen, I understand that you already applied this patch but given how
> horrible the proposed API is and that's even undocumented in this
> patch, please reconsider this. If this is released, the API is set in
> stone and, frankly, it's very user unfriendly this way.
>
> Paul, could you please prepare a patch that would introduce a more sane
> API? I'd strongly prefer what I described under "third" but should you
> strongly disagree, at least implement "second" and document the
> currently known flag values.
>
> Thanks,
>
>   Jiri

Matching name was from the idea that we are doing is matching.
And regarding documentation/flag names I didn't want tc tool to be need 
of a update each time a new flag is introduced,
But I guess I can add two options like with ip_proto where you can 
specify known flags by name but can also give a value.
What do you think about that?

flags <FLAGS> / <HEX'/'HEX>
FLAGS => frag/no_frag/tcp_syn/no_tcp_syn ['|'<FLAGS>]*
e.g: flags frag|no_tcp_syn or flags 0x01/0x15
and the mask will have a on bits corresponds only to those flags specified.