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

On Fri, 29 Sep 2017 20:06:09 -0700
Alexei Starovoitov [off-list ref] wrote:

quoted

+/*** 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.

quoted

+
+	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