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

On Tue, 16 Jun 2020 18:11:33 +0800
Hangbin Liu [off-list ref] wrote:

HI Jesper,

On Tue, Jun 16, 2020 at 10:55:06AM +0200, Jesper Dangaard Brouer wrote:

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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.

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And as I wrote below you also need to update frame_sz.
  

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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.

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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.
 

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+
+	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