netdev - Re: [PATCHv4 bpf-next 1/2] xdp: add a new helper for dev map multicast support

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Date:   Tue, 16 Jun 2020 18:11:33 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Jiri Benc <jbenc@...hat.com>,
        Eelco Chaudron <echaudro@...hat.com>, ast@...nel.org,
        Daniel Borkmann <daniel@...earbox.net>,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
Subject: Re: [PATCHv4 bpf-next 1/2] xdp: add a new helper for dev map
 multicast support

HI Jesper,

On Tue, Jun 16, 2020 at 10:55:06AM +0200, Jesper Dangaard Brouer wrote:
> > Is there anything else I should do except add the following line?
> > 	nxdpf->mem.type = MEM_TYPE_PAGE_ORDER0;
> 
> You do realize that you also have copied over the mem.id, right?

Thanks for the reminding. To confirm, set mem.id to 0 is enough, right?
> 
> And as I wrote below you also need to update frame_sz.
> 
> > > 
> > > You also need to update xdpf->frame_sz, as you also cannot assume it is
> > > the same.  
> > 
> > Won't the memcpy() copy xdpf->frame_sz to nxdpf? 
> 
> You obviously cannot use the frame_sz from the existing frame, as you
> just allocated a new page for the new xdp_frame, that have another size
> (here PAGE_SIZE).

Thanks, I didn't understand the frame_sz correctly before.
> 
> 
> > And I didn't see xdpf->frame_sz is set in xdp_convert_zc_to_xdp_frame(),
> > do we need a fix?
> 
> Good catch, that sounds like a bug, that should be fixed.
> Will you send a fix?

OK, I will.

> 
> 
> > > > +
> > > > +	nxdpf = addr;
> > > > +	nxdpf->data = addr + headroom;
> > > > +
> > > > +	return nxdpf;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(xdpf_clone);  
> > > 
> > > 
> > > struct xdp_frame {
> > > 	void *data;
> > > 	u16 len;
> > > 	u16 headroom;
> > > 	u32 metasize:8;
> > > 	u32 frame_sz:24;
> > > 	/* Lifetime of xdp_rxq_info is limited to NAPI/enqueue time,
> > > 	 * while mem info is valid on remote CPU.
> > > 	 */
> > > 	struct xdp_mem_info mem;
> > > 	struct net_device *dev_rx; /* used by cpumap */
> > > };
> > >   
> > 
> 
> struct xdp_mem_info {
> 	u32                        type;                 /*     0     4 */
> 	u32                        id;                   /*     4     4 */
> 
> 	/* size: 8, cachelines: 1, members: 2 */
> 	/* last cacheline: 8 bytes */
> };
> 

Is this a struct reference or you want to remind me something else?

Thanks
Hangbin