netdev - Re: [PATCH net-next 1/6] xdp: introduce mb in xdp_buff/xdp

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Date:   Sun, 23 Aug 2020 17:08:30 +0300
From:   Shay Agroskin <shayagr@...zon.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
CC:     <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
        <davem@...emloft.net>, <lorenzo.bianconi@...hat.com>,
        <brouer@...hat.com>, <echaudro@...hat.com>, <sameehj@...zon.com>,
        <kuba@...nel.org>
Subject: Re: [PATCH net-next 1/6] xdp: introduce mb in xdp_buff/xdp_frame


Lorenzo Bianconi <lorenzo@...nel.org> writes:

> Introduce multi-buffer bit (mb) in xdp_frame/xdp_buffer to 
> specify
> if shared_info area has been properly initialized for non-linear
> xdp buffers
>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
>  include/net/xdp.h | 8 ++++++--
>  net/core/xdp.c    | 1 +
>  2 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index 3814fb631d52..42f439f9fcda 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -72,7 +72,8 @@ struct xdp_buff {
>  	void *data_hard_start;
>  	struct xdp_rxq_info *rxq;
>  	struct xdp_txq_info *txq;
> -	u32 frame_sz; /* frame size to deduce 
> data_hard_end/reserved tailroom*/
> +	u32 frame_sz:31; /* frame size to deduce 
> data_hard_end/reserved tailroom*/
> +	u32 mb:1; /* xdp non-linear buffer */
>  };
>  
>  /* Reserve memory area at end-of data area.
> @@ -96,7 +97,8 @@ struct xdp_frame {
>  	u16 len;
>  	u16 headroom;
>  	u32 metasize:8;
> -	u32 frame_sz:24;
> +	u32 frame_sz:23;
> +	u32 mb:1; /* xdp non-linear frame */

Although this issue wasn't introduced with this patch, why not 
make frame_sz field to be the same size in xdp_buff and xdp_frame 
?

thanks,
Shay
>  	/* Lifetime of xdp_rxq_info is limited to NAPI/enqueue 
>  time,
>  	 * while mem info is valid on remote CPU.
>  	 */
> @@ -141,6 +143,7 @@ void xdp_convert_frame_to_buff(struct 
> xdp_frame *frame, struct xdp_buff *xdp)
>  	xdp->data_end = frame->data + frame->len;
>  	xdp->data_meta = frame->data - frame->metasize;
>  	xdp->frame_sz = frame->frame_sz;
> +	xdp->mb = frame->mb;
>  }
>  
>  static inline
> @@ -167,6 +170,7 @@ int xdp_update_frame_from_buff(struct 
> xdp_buff *xdp,
>  	xdp_frame->headroom = headroom - sizeof(*xdp_frame);
>  	xdp_frame->metasize = metasize;
>  	xdp_frame->frame_sz = xdp->frame_sz;
> +	xdp_frame->mb = xdp->mb;
>  
>  	return 0;
>  }
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 48aba933a5a8..884f140fc3be 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -454,6 +454,7 @@ struct xdp_frame 
> *xdp_convert_zc_to_xdp_frame(struct xdp_buff *xdp)
>  	xdpf->headroom = 0;
>  	xdpf->metasize = metasize;
>  	xdpf->frame_sz = PAGE_SIZE;
> +	xdpf->mb = xdp->mb;
>  	xdpf->mem.type = MEM_TYPE_PAGE_ORDER0;
>  
>  	xsk_buff_free(xdp);