Re: [PATCH net-next 5/5] xdp: get tracepoints xdp_exception and xdp_redirect in sync

On Tue, 22 Aug 2017 23:30:21 +0200
Daniel Borkmann [off-list ref] wrote:

On 08/22/2017 10:47 PM, Jesper Dangaard Brouer wrote:

quoted

Remove the net_device string name from the xdp_exception tracepoint,
like the xdp_redirect tracepoint.

Align the TP_STRUCT to have common entries between these two
tracepoint.

Signed-off-by: Jesper Dangaard Brouer <redacted>
---
  include/trace/events/xdp.h |   24 ++++++++++++------------
  1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h
index 7511bed80558..6495b0d9d5c7 100644
--- a/include/trace/events/xdp.h
+++ b/include/trace/events/xdp.h

@@ -31,22 +31,22 @@ TRACE_EVENT(xdp_exception,
  	TP_ARGS(dev, xdp, act),

  	TP_STRUCT__entry(
-		__string(name, dev->name)
  		__array(u8, prog_tag, 8)
  		__field(u32, act)
+		__field(int, ifindex)
  	),

  	TP_fast_assign(
  		BUILD_BUG_ON(sizeof(__entry->prog_tag) != sizeof(xdp->tag));
  		memcpy(__entry->prog_tag, xdp->tag, sizeof(xdp->tag));
-		__assign_str(name, dev->name);
-		__entry->act = act;
+		__entry->act		= act;
+		__entry->ifindex	= dev->ifindex;
  	),
 

[...]

quoted

  TRACE_EVENT(xdp_redirect,

@@ -57,26 +57,26 @@ TRACE_EVENT(xdp_redirect,
  	TP_ARGS(from_index, to_index, xdp, act, err),

  	TP_STRUCT__entry(
-		__field(int, from_index)
-		__field(int, to_index)
  		__array(u8, prog_tag, 8)
  		__field(u32, act)
+		__field(int, from_index)
+		__field(int, to_index)
  		__field(int, err)
  	),

  	TP_fast_assign(
  		BUILD_BUG_ON(sizeof(__entry->prog_tag) != sizeof(xdp->tag));
  		memcpy(__entry->prog_tag, xdp->tag, sizeof(xdp->tag));
+		__entry->act		= act;
  		__entry->from_index	= from_index;
  		__entry->to_index	= to_index;
-		__entry->act = act;  

If you already get them in sync, could you also make it consistent
that for both tracepoints in TP_ARGS() we use either ifindex
directly or device pointer and extract it from TP_fast_assign().
Right now, it's mixed.

I did this because, in the (bpf_redirect)_map case, I was hoping that
"from_index" could be come the index from the map.  Looking closer at
the devmap design, I cannot see how we can ever know what (the bpf_prog
thinks) is the corresponding map-ingress/from_index.

Based on that, I think we can/should use the device pointer as arg (as
you suggested). And then rename "from_index" to "ifindex", where
ifindex is the XDP ifindex the xdp_buff arrived on.

I guess we can keep the "to_index".  We also need to extend the
tracepoint args with a "map", to let the trace user tell whether the
"to_index" is an ifindex or a map-index.

I'll code this up and submit at V2.
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer