netdev - Re: [PATCH v5 bpf-next 03/14] xdp: add xdp_shared

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Message-ID: <c7434cfc-66ed-8795-06b1-ec296eefc484@mojatatu.com>
Date:   Mon, 21 Dec 2020 08:00:29 -0500
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Shay Agroskin <shayagr@...zon.com>,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>,
        Saeed Mahameed <saeed@...nel.org>,
        Lorenzo Bianconi <lorenzo@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        ast@...nel.org, daniel@...earbox.net, sameehj@...zon.com,
        john.fastabend@...il.com, dsahern@...nel.org, echaudro@...hat.com,
        jasowang@...hat.com
Subject: Re: [PATCH v5 bpf-next 03/14] xdp: add xdp_shared_info data structure

On 2020-12-21 4:01 a.m., Jesper Dangaard Brouer wrote:
> On Sat, 19 Dec 2020 10:30:57 -0500

>> Sorry to interject:
>> Does it make sense to use it to store arbitrary metadata or a scratchpad
>> in this space? Something equivalent to skb->cb which is lacking in
>> XDP.
> 
> Well, XDP have the data_meta area.  But difficult to rely on because a
> lot of driver don't implement it.  And Saeed and I plan to use this
> area and populate it with driver info from RX-descriptor.
> 

What i was thinking is some scratch pad that i can write to within
an XDP prog (not driver); example, in a prog array map the scratch
pad is written by one program in the array and read by another later on.
skb->cb allows for that. Unless you mean i can already write to some
XDP data_meta area?

cheers,
jamal