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Date:   Thu, 16 Jan 2020 12:24:00 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        David Miller <davem@...emloft.net>,
        Björn Töpel <bjorn.topel@...il.com>,
        John Fastabend <john.fastabend@...il.com>, brouer@...hat.com
Subject: Re: [PATCH bpf-next v2 1/2] xdp: Move devmap bulk queue into struct
 net_device

On Wed, 15 Jan 2020 23:11:21 +0100
Toke Høiland-Jørgensen <toke@...hat.com> wrote:

> Jesper Dangaard Brouer <brouer@...hat.com> writes:
> 
> > On Mon, 13 Jan 2020 19:10:55 +0100
> > Toke Høiland-Jørgensen <toke@...hat.com> wrote:
> >  
> >> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> >> index da9c832fc5c8..030d125c3839 100644
> >> --- a/kernel/bpf/devmap.c
> >> +++ b/kernel/bpf/devmap.c  
> > [...]  
> >> @@ -346,8 +340,7 @@ static int bq_xmit_all(struct xdp_bulk_queue *bq, u32 flags)
> >>  out:
> >>  	bq->count = 0;
> >>  
> >> -	trace_xdp_devmap_xmit(&obj->dtab->map, obj->idx,
> >> -			      sent, drops, bq->dev_rx, dev, err);
> >> +	trace_xdp_devmap_xmit(NULL, 0, sent, drops, bq->dev_rx, dev, err);  
> >
> > Hmm ... I don't like that we lose the map_id and map_index identifier.
> > This is part of our troubleshooting interface.  
> 
> Hmm, I guess I can take another look at whether there's a way to avoid
> that. Any ideas?

Looking at the code and the other tracepoints...

I will actually suggest to remove these two arguments, because the
trace_xdp_redirect_map tracepoint also contains the ifindex'es, and to
troubleshoot people can record both tracepoints and do the correlation
themselves.

When changing the tracepoint I would like to keep member 'drops' and
'sent' at the same struct offsets.  As our xdp_monitor example reads
these and I hope we can kept it working this way.

I've coded it up, and tested it.  The new xdp_monitor will work on
older kernels, but the old xdp_monitor will fail attaching on newer
kernels. I think this is fair enough, as we are backwards compatible.


[PATCH] devmap: adjust tracepoing after Tokes changes

From: Jesper Dangaard Brouer <brouer@...hat.com>

Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---
 include/trace/events/xdp.h     |   29 ++++++++++++-----------------
 kernel/bpf/devmap.c            |    2 +-
 samples/bpf/xdp_monitor_kern.c |    8 +++-----
 3 files changed, 16 insertions(+), 23 deletions(-)

diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h
index cf568a38f852..f1e64689ce94 100644
--- a/include/trace/events/xdp.h
+++ b/include/trace/events/xdp.h
@@ -247,43 +247,38 @@ TRACE_EVENT(xdp_cpumap_enqueue,
 
 TRACE_EVENT(xdp_devmap_xmit,
 
-	TP_PROTO(const struct bpf_map *map, u32 map_index,
-		 int sent, int drops,
-		 const struct net_device *from_dev,
-		 const struct net_device *to_dev, int err),
+	TP_PROTO(const struct net_device *from_dev,
+		 const struct net_device *to_dev,
+		 int sent, int drops, int err),
 
-	TP_ARGS(map, map_index, sent, drops, from_dev, to_dev, err),
+	TP_ARGS(from_dev, to_dev, sent, drops, err),
 
 	TP_STRUCT__entry(
-		__field(int, map_id)
+		__field(int, from_ifindex)
 		__field(u32, act)
-		__field(u32, map_index)
+		__field(int, to_ifindex)
 		__field(int, drops)
 		__field(int, sent)
-		__field(int, from_ifindex)
-		__field(int, to_ifindex)
 		__field(int, err)
 	),
 
 	TP_fast_assign(
-		__entry->map_id		= map ? map->id : 0;
+		__entry->from_ifindex	= from_dev->ifindex;
 		__entry->act		= XDP_REDIRECT;
-		__entry->map_index	= map_index;
+		__entry->to_ifindex	= to_dev->ifindex;
 		__entry->drops		= drops;
 		__entry->sent		= sent;
-		__entry->from_ifindex	= from_dev->ifindex;
-		__entry->to_ifindex	= to_dev->ifindex;
 		__entry->err		= err;
 	),
 
 	TP_printk("ndo_xdp_xmit"
-		  " map_id=%d map_index=%d action=%s"
+		  " from_ifindex=%d to_ifindex=%d action=%s"
 		  " sent=%d drops=%d"
-		  " from_ifindex=%d to_ifindex=%d err=%d",
-		  __entry->map_id, __entry->map_index,
+		  " err=%d",
+		  __entry->from_ifindex, __entry->to_ifindex,
 		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB),
 		  __entry->sent, __entry->drops,
-		  __entry->from_ifindex, __entry->to_ifindex, __entry->err)
+		  __entry->err)
 );
 
 /* Expect users already include <net/xdp.h>, but not xdp_priv.h */
diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index db32272c4f77..1b4bfe4e06d6 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -340,7 +340,7 @@ static int bq_xmit_all(struct xdp_dev_bulk_queue *bq, u32 flags)
 out:
 	bq->count = 0;
 
-	trace_xdp_devmap_xmit(NULL, 0, sent, drops, bq->dev_rx, dev, err);
+	trace_xdp_devmap_xmit(bq->dev_rx, dev, sent, drops, err);
 	bq->dev_rx = NULL;
 	__list_del_clearprev(&bq->flush_node);
 	return 0;
diff --git a/samples/bpf/xdp_monitor_kern.c b/samples/bpf/xdp_monitor_kern.c
index ad10fe700d7d..39458a44472e 100644
--- a/samples/bpf/xdp_monitor_kern.c
+++ b/samples/bpf/xdp_monitor_kern.c
@@ -222,14 +222,12 @@ struct bpf_map_def SEC("maps") devmap_xmit_cnt = {
  */
 struct devmap_xmit_ctx {
 	u64 __pad;		// First 8 bytes are not accessible by bpf code
-	int map_id;		//	offset:8;  size:4; signed:1;
+	int from_ifindex;	//	offset:8;  size:4; signed:1;
 	u32 act;		//	offset:12; size:4; signed:0;
-	u32 map_index;		//	offset:16; size:4; signed:0;
+	int to_ifindex; 	//	offset:16; size:4; signed:1;
 	int drops;		//	offset:20; size:4; signed:1;
 	int sent;		//	offset:24; size:4; signed:1;
-	int from_ifindex;	//	offset:28; size:4; signed:1;
-	int to_ifindex;		//	offset:32; size:4; signed:1;
-	int err;		//	offset:36; size:4; signed:1;
+	int err;		//	offset:28; size:4; signed:1;
 };
 
 SEC("tracepoint/xdp/xdp_devmap_xmit")

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