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Date: Mon, 03 Jul 2023 14:06:46 -0700
From: John Fastabend <john.fastabend@gmail.com>
To: Larysa Zaremba <larysa.zaremba@intel.com>,
bpf@vger.kernel.org
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CC: Larysa Zaremba <larysa.zaremba@intel.com>, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, David Ahern <dsahern@gmail.com>, Jakub Kicinski <kuba@kernel.org>, Willem de Bruijn <willemb@google.com>, Jesper Dangaard Brouer <brouer@redhat.com>, Anatoly Burakov <anatoly.burakov@intel.com>, Alexander Lobakin <alexandr.lobakin@intel.com>, Magnus Karlsson <magnus.karlsson@gmail.com>, Maryam Tahhan <mtahhan@redhat.com>, xdp-hints@xdp-project.net, netdev@vger.kernel.org, Aleksander Lobakin <aleksander.lobakin@intel.com>
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Subject: [xdp-hints] Re: [PATCH bpf-next v2 15/20] net, xdp: allow metadata > 32
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Larysa Zaremba wrote:
> From: Aleksander Lobakin <aleksander.lobakin@intel.com>
>
> When using XDP hints, metadata sometimes has to be much bigger
> than 32 bytes. Relax the restriction, allow metadata larger than 32 bytes
> and make __skb_metadata_differs() work with bigger lengths.
>
> Now size of metadata is only limited by the fact it is stored as u8
> in skb_shared_info, so maximum possible value is 255. Other important
> conditions, such as having enough space for xdp_frame building, are already
> checked in bpf_xdp_adjust_meta().
>
> The requirement of having its length aligned to 4 bytes is still
> valid.
>
> Signed-off-by: Aleksander Lobakin <aleksander.lobakin@intel.com>
> Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
> ---
> include/linux/skbuff.h | 13 ++++++++-----
> include/net/xdp.h | 7 ++++++-
> 2 files changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 91ed66952580..cd49cdd71019 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -4209,10 +4209,13 @@ static inline bool __skb_metadata_differs(const struct sk_buff *skb_a,
> {
> const void *a = skb_metadata_end(skb_a);
> const void *b = skb_metadata_end(skb_b);
> - /* Using more efficient varaiant than plain call to memcmp(). */
> -#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && BITS_PER_LONG == 64
Why are we removing the ifdef here? Its adding a runtime 'if' when its not
necessary. I would keep the ifdef and simply add the default case
in the switch.