netdev - Re: [PATCH v5 bpf 03/11] xsk: fix usage of multi-buffer BPF helpers for ZC XDP

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Date: Wed, 24 Jan 2024 13:02:21 +0100
From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: <bpf@...r.kernel.org>, <ast@...nel.org>, <daniel@...earbox.net>,
	<andrii@...nel.org>, <netdev@...r.kernel.org>, <magnus.karlsson@...el.com>,
	<bjorn@...nel.org>, <echaudro@...hat.com>, <lorenzo@...nel.org>,
	<martin.lau@...ux.dev>, <tirthendu.sarkar@...el.com>,
	<john.fastabend@...il.com>, <horms@...nel.org>
Subject: Re: [PATCH v5 bpf 03/11] xsk: fix usage of multi-buffer BPF helpers
 for ZC XDP

On Tue, Jan 23, 2024 at 05:53:17PM -0800, Jakub Kicinski wrote:
> On Mon, 22 Jan 2024 23:16:02 +0100 Maciej Fijalkowski wrote:
> >  
> > +static void __shrink_data(struct xdp_buff *xdp, struct xdp_mem_info *mem_info,
> > +			  skb_frag_t *frag, int shrink)
> > +{
> > +	if (mem_info->type == MEM_TYPE_XSK_BUFF_POOL)
> > +		xsk_buff_get_tail(xdp)->data_end -= shrink;
> > +	skb_frag_size_sub(frag, shrink);
> 
> nit: this has just one caller, why not inline these 3 lines?

we usually rely on compiler to do that, we have the rule "no inlines in
source files", no?

> 
> > +}
> > +
> > +static bool shrink_data(struct xdp_buff *xdp, skb_frag_t *frag, int shrink)
> 
> nit: prefix the function name, please

will rename to bpf_xdp_shrink_data(). Thanks for taking a look!

> 
> > +{
> > +	struct xdp_mem_info *mem_info = &xdp->rxq->mem;
> > +
> > +	if (skb_frag_size(frag) == shrink) {
> > +		struct page *page = skb_frag_page(frag);
> > +		struct xdp_buff *zc_frag = NULL;
> > +
> > +		if (mem_info->type == MEM_TYPE_XSK_BUFF_POOL) {
> > +			zc_frag = xsk_buff_get_tail(xdp);
> > +
> > +			xsk_buff_del_tail(zc_frag);
> > +		}
> > +
> > +		__xdp_return(page_address(page), mem_info, false, zc_frag);
> > +		return true;
> > +	}
> > +	__shrink_data(xdp, mem_info, frag, shrink);
> > +	return false;