linux-kernel - Re: [PATCH net-next v5 11/19] xdp: add generic xdp_buff_add

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Message-ID: <20241115184059.3b369970@kernel.org>
Date: Fri, 15 Nov 2024 18:40:59 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Toke
 Høiland-Jørgensen <toke@...hat.com>, Alexei
 Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, John
 Fastabend <john.fastabend@...il.com>, Andrii Nakryiko <andrii@...nel.org>,
 Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Stanislav Fomichev
 <sdf@...ichev.me>, Magnus Karlsson <magnus.karlsson@...el.com>,
 nex.sw.ncis.osdt.itp.upstreaming@...el.com, bpf@...r.kernel.org,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v5 11/19] xdp: add generic xdp_buff_add_frag()

On Wed, 13 Nov 2024 16:24:34 +0100 Alexander Lobakin wrote:
> +static inline bool __xdp_buff_add_frag(struct xdp_buff *xdp, struct page *page,
> +				       u32 offset, u32 size, u32 truesize,
> +				       bool try_coalesce)
> +{
> +	struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
> +	skb_frag_t *prev;
> +	u32 nr_frags;
> +
> +	if (!xdp_buff_has_frags(xdp)) {
> +		xdp_buff_set_frags_flag(xdp);
> +
> +		nr_frags = 0;
> +		sinfo->xdp_frags_size = 0;
> +		sinfo->xdp_frags_truesize = 0;
> +
> +		goto fill;
> +	}
> +
> +	nr_frags = sinfo->nr_frags;
> +	if (unlikely(nr_frags == MAX_SKB_FRAGS))
> +		return false;
> +
> +	prev = &sinfo->frags[nr_frags - 1];
> +	if (try_coalesce && page == skb_frag_page(prev) &&
> +	    offset == skb_frag_off(prev) + skb_frag_size(prev))
> +		skb_frag_size_add(prev, size);

don't we have to release the reference if we coalesced?

> +	else
> +fill:
> +		__skb_fill_page_desc_noacc(sinfo, nr_frags++, page,
> +					   offset, size);
> +
> +	sinfo->nr_frags = nr_frags;
> +	sinfo->xdp_frags_size += size;
> +	sinfo->xdp_frags_truesize += truesize;
> +
> +	return true;
> +}