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

From: Jesper Dangaard Brouer <[email-masked]>
Date: Tue, 16 Jun 2020 16:38:04 +0200

On Tue, 16 Jun 2020 18:11:33 +0800
Hangbin Liu <[email-masked]> wrote:

> 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?

Yes.

> > 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.

Thanks.
 
> >   
> > > > > +
> > > > > +	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?

This is just a struct reference to help the readers of this email.
I had to lookup the struct to review this code, so I included it to
save time for other reviewers.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer