netdev - Re: [PATCH v18 bpf-next 12/23] bpf: add multi-buff support to the bpf_xdp_adjust

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Message-ID: <20211116065931.054266c0@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 16 Nov 2021 06:59:31 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        lorenzo.bianconi@...hat.com, davem@...emloft.net, ast@...nel.org,
        daniel@...earbox.net, shayagr@...zon.com, john.fastabend@...il.com,
        dsahern@...nel.org, brouer@...hat.com, echaudro@...hat.com,
        jasowang@...hat.com, alexander.duyck@...il.com, saeed@...nel.org,
        maciej.fijalkowski@...el.com, magnus.karlsson@...el.com,
        tirthendu.sarkar@...el.com, toke@...hat.com
Subject: Re: [PATCH v18 bpf-next 12/23] bpf: add multi-buff support to the
 bpf_xdp_adjust_tail() API

On Mon, 15 Nov 2021 23:33:06 +0100 Lorenzo Bianconi wrote:
> +	if (!rxq->frag_size || rxq->frag_size > xdp->frame_sz)

Why the latter check?

> +		return -EOPNOTSUPP;
> +
> +	tailroom = rxq->frag_size - skb_frag_size(frag) - skb_frag_off(frag);

Looks good. We can adjust/extend the exact semantics as drivers add
support. Important part is we should be safe from negligence.

Acked-by: Jakub Kicinski <kuba@...nel.org>