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

Hangbin Liu
2020-06-16T10:11:46Z

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