Subject: Re: [PATCH net-next v5 11/19] xdp: add generic xdp_buff_add_frag()

From: Jakub Kicinski <[email-masked]>
Date: Fri, 15 Nov 2024 18:40:59 -0800

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;
> +}