netdev - Re: [PATCH iproute2 5/5] bpf: implement btf handling and map annotation

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Message-ID: <20180719001143.gjh77spvcnujblkc@kafai-mbp.dhcp.thefacebook.com>
Date:   Wed, 18 Jul 2018 17:11:43 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
CC:     Daniel Borkmann <daniel@...earbox.net>, <dsahern@...il.com>,
        <alexei.starovoitov@...il.com>, <netdev@...r.kernel.org>
Subject: Re: [PATCH iproute2 5/5] bpf: implement btf handling and map
 annotation

On Wed, Jul 18, 2018 at 11:13:37AM -0700, Jakub Kicinski wrote:
> On Wed, 18 Jul 2018 11:33:22 +0200, Daniel Borkmann wrote:
> > On 07/18/2018 10:42 AM, Daniel Borkmann wrote:
> > > On 07/18/2018 02:27 AM, Jakub Kicinski wrote:  
> > >> On Wed, 18 Jul 2018 01:31:22 +0200, Daniel Borkmann wrote:  
> > >>>   # bpftool map dump id 386
> > >>>    [{
> > >>>         "key": 0,
> > >>>         "value": {
> > >>>             "": {
> > >>>                 "value": 0,
> > >>>                 "ifindex": 0,
> > >>>                 "mac": []
> > >>>             }
> > >>>         }
> > >>>     },{
> > >>>         "key": 1,
> > >>>         "value": {
> > >>>             "": {
> > >>>                 "value": 0,
> > >>>                 "ifindex": 0,
> > >>>                 "mac": []
> > >>>             }
> > >>>         }
> > >>>     },{
> > >>>   [...]  
> > >>
> > >> Ugh, the empty keys ("") look worrying, we should probably improve
> > >> handling of anonymous structs in bpftool :S  
> > > 
> > > Yeah agree, I think it would be nice to see a more pahole style dump
> > > where we have types and member names along with the value as otherwise
> > > it might be a bit confusing.  
> > 
> > Another feature that would be super useful imho would be in the /single/
> > map view e.g. 'bpftool map show id 123' to have a detailed BTF key+value
> > type dump, so in addition to the basic map info we show pahole like info
> > of the structs with length/offsets.
> 
> That sounds good!  We could also consider adding a btf object and
> commands to interrogate BTF types in the kernel in general..  Perhaps
> then we could add something like bpftool btf describe map id 123.
+1 on the btf subcommand.

> 
> Having the single map view show more information seems interesting, but
> I wonder if it could be surprising.  Is there precedent for such
> behaviour?
Having everything in one page (map show id 123) could be interesting.
One thing is the pahole-like output may be quite long?
e.g. the member of a struct could itself be another struct.

Not sure how the pahole-like output may look like in json though.