Subject: Re: [net-next V2 PATCH 5/5] samples/bpf: add cpumap sample program xdp_redirect_cpu

From: Jesper Dangaard Brouer <[email-masked]>
Date: Mon, 2 Oct 2017 14:07:23 +0200

On Fri, 29 Sep 2017 20:06:09 -0700
Alexei Starovoitov <[email-masked]> wrote:

> > +/*** Trace point code ***/
> > +
> > +/* Tracepoint format: /sys/kernel/debug/tracing/events/xdp/xdp_redirect/format
> > + * Code in:                kernel/include/trace/events/xdp.h
> > + */
> > +struct xdp_redirect_ctx {
> > +	unsigned short common_type;	//	offset:0;  size:2; signed:0;
> > +	unsigned char common_flags;	//	offset:2;  size:1; signed:0;
> > +	unsigned char common_preempt_count;//	offset:3;  size:1; signed:0;
> > +	int common_pid;			//	offset:4;  size:4; signed:1;  
> 
> this part is not right. First 8 bytes are not accessible by bpf code.
> Please use __u64 pad; or similar here.

I've corrected this in V3.

Can you explain why BPF cannot access these (first 8 bytes) struct members?

> Just noticed that samples/bpf/xdp_monitor_kern.c has the same problem.
> 
> > +
> > +	int prog_id;			//	offset:8;  size:4; signed:1;
> > +	u32 act;			//	offset:12  size:4; signed:0;
> > +	int ifindex;			//	offset:16  size:4; signed:1;
> > +	int err;			//	offset:20  size:4; signed:1;
> > +	int to_ifindex;			//	offset:24  size:4; signed:1;
> > +	u32 map_id;			//	offset:28  size:4; signed:0;
> > +	int map_index;			//	offset:32  size:4; signed:1;
> > +};					//	offset:36  
> 
> the second part of fields is correct.

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