netdev - Re: [PATCH net v2] xdp, net: fix for construct skb by xdp inside xsk zc rx

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Date:   Tue, 29 Jun 2021 18:55:59 +0200
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Björn Töpel <bjorn@...nel.org>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        Krzysztof Kazimierczak <krzysztof.kazimierczak@...el.com>,
        Ong Boon Leong <boon.leong.ong@...el.com>,
        intel-wired-lan@...ts.osuosl.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH net v2] xdp, net: fix for construct skb by xdp inside xsk
 zc rx

On 28/06/2021 12.47, Maciej Fijalkowski wrote:

> +static __always_inline struct sk_buff *
> +xdp_construct_skb(struct xdp_buff *xdp, struct napi_struct *napi)
> +{

I don't like the generic name "xdp_construct_skb".

What about calling it "xdp_copy_construct_skb", because below is 
memcpy'ing the data.

Functions that use this call free (or recycle) the memory backing the 
packet, after calling this function.

(I'm open to other naming suggestions)


> +	unsigned int metasize;
> +	unsigned int datasize;
> +	unsigned int headroom;
> +	struct sk_buff *skb;
> +	unsigned int len;
> +
> +	/* this include metasize */
> +	datasize = xdp->data_end  - xdp->data_meta;
> +	metasize = xdp->data      - xdp->data_meta;
> +	headroom = xdp->data_meta - xdp->data_hard_start;
> +	len      = xdp->data_end  - xdp->data_hard_start;
> +
> +	/* allocate a skb to store the frags */
> +	skb = __napi_alloc_skb(napi, len, GFP_ATOMIC | __GFP_NOWARN);
> +	if (unlikely(!skb))
> +		return NULL;
> +
> +	skb_reserve(skb, headroom);
> +	memcpy(__skb_put(skb, datasize), xdp->data_meta, datasize);
> +	if (metasize) {
> +		__skb_pull(skb, metasize);
> +		skb_metadata_set(skb, metasize);
> +	}
> +
> +	return skb;
> +}