netdev - Re: [PATCH v2 bpf-next] xdp: introduce convert_to_xdp

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Message-ID: <20200528140419.GB24961@pc-9.home>
Date:   Thu, 28 May 2020 16:04:19 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, ast@...nel.org,
        davem@...emloft.net, brouer@...hat.com,
        lorenzo.bianconi@...hat.com, dsahern@...nel.org,
        toshiaki.makita1@...il.com
Subject: Re: [PATCH v2 bpf-next] xdp: introduce convert_to_xdp_buff utility
 routine

On Wed, May 27, 2020 at 11:28:03AM +0200, Lorenzo Bianconi wrote:
> Introduce convert_to_xdp_buff utility routine to initialize xdp_buff
> fields from xdp_frames ones. Rely on convert_to_xdp_buff in veth xdp
> code
> 
> Suggested-by: Jesper Dangaard Brouer <brouer@...hat.com>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
> Changes since v1:
> - rely on frame->data pointer to compute xdp->data_hard_start one
> ---
>  drivers/net/veth.c |  6 +-----
>  include/net/xdp.h  | 10 ++++++++++
>  2 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/veth.c b/drivers/net/veth.c
> index b586d2fa5551..9f91e79b7823 100644
> --- a/drivers/net/veth.c
> +++ b/drivers/net/veth.c
> @@ -575,11 +575,7 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq,
>  		struct xdp_buff xdp;
>  		u32 act;
>  
> -		xdp.data_hard_start = hard_start;
> -		xdp.data = frame->data;
> -		xdp.data_end = frame->data + frame->len;
> -		xdp.data_meta = frame->data - frame->metasize;
> -		xdp.frame_sz = frame->frame_sz;
> +		convert_to_xdp_buff(frame, &xdp);
>  		xdp.rxq = &rq->xdp_rxq;
>  
>  		act = bpf_prog_run_xdp(xdp_prog, &xdp);
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index 90f11760bd12..df99d5d267b2 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -106,6 +106,16 @@ void xdp_warn(const char *msg, const char *func, const int line);
>  
>  struct xdp_frame *xdp_convert_zc_to_xdp_frame(struct xdp_buff *xdp);
>  
> +static inline
> +void convert_to_xdp_buff(struct xdp_frame *frame, struct xdp_buff *xdp)
> +{
> +	xdp->data_hard_start = frame->data - frame->headroom - sizeof(*frame);
> +	xdp->data = frame->data;
> +	xdp->data_end = frame->data + frame->len;
> +	xdp->data_meta = frame->data - frame->metasize;
> +	xdp->frame_sz = frame->frame_sz;
> +}

>From an API PoV, could we please prefix these with xdp_*(). Looks like there
is also convert_to_xdp_frame() as an outlier in there, but lets clean these
up once in the tree to avoid getting this more messy and harder to fix later
on. How about:

  - xdp_convert_frame_to_buff()
  - xdp_convert_buff_to_frame()

This will have both more self-documented and makes it obvious from where to
where we convert something.

Thanks,
Daniel