netdev - Re: [PATCH v8 bpf-next 01/14] xdp: introduce mb in xdp_buff/xdp

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Date:   Fri, 9 Apr 2021 18:03:31 +0200
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        lorenzo.bianconi@...hat.com, davem@...emloft.net, kuba@...nel.org,
        ast@...nel.org, daniel@...earbox.net, shayagr@...zon.com,
        sameehj@...zon.com, john.fastabend@...il.com, dsahern@...nel.org,
        brouer@...hat.com, echaudro@...hat.com, jasowang@...hat.com,
        alexander.duyck@...il.com, saeed@...nel.org,
        maciej.fijalkowski@...el.com
Subject: Re: [PATCH v8 bpf-next 01/14] xdp: introduce mb in xdp_buff/xdp_frame

> On Thu, Apr 08, 2021 at 02:50:53PM +0200, Lorenzo Bianconi wrote:
> > Introduce multi-buffer bit (mb) in xdp_frame/xdp_buffer data structure
> > in order to specify if this is a linear buffer (mb = 0) or a multi-buffer
> > frame (mb = 1). In the latter case the shared_info area at the end of the
> > first buffer will be properly initialized to link together subsequent
> > buffers.
> > 
> > Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> > ---
> >  include/net/xdp.h | 11 +++++++++--
> >  1 file changed, 9 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/net/xdp.h b/include/net/xdp.h
> > index a5bc214a49d9..842580a61563 100644
> > --- a/include/net/xdp.h
> > +++ b/include/net/xdp.h
> > @@ -73,7 +73,10 @@ 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
> > +			  */
> 
> This comment would have fit just fine on one line:
> 
> 	/* frame size to deduce data_hard_end/reserved tailroom */

ack, thx I will fix it in v9

Regards,
Lorenzo

> 
> > +	u32 mb:1; /* xdp non-linear buffer */
> >  };
> >  
> >  static __always_inline void
> > @@ -81,6 +84,7 @@ xdp_init_buff(struct xdp_buff *xdp, u32 frame_sz, struct xdp_rxq_info *rxq)
> >  {
> >  	xdp->frame_sz = frame_sz;
> >  	xdp->rxq = rxq;
> > +	xdp->mb = 0;
> >  }
> >  
> >  static __always_inline void
> > @@ -116,7 +120,8 @@ 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 */
> >  	/* Lifetime of xdp_rxq_info is limited to NAPI/enqueue time,
> >  	 * while mem info is valid on remote CPU.
> >  	 */
> > @@ -179,6 +184,7 @@ 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
> > @@ -205,6 +211,7 @@ 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;
> >  }
> > -- 
> > 2.30.2
> > 

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