[PATCH bpf-next v4 1/2] bpf, xdp: Add tracepoint to xdp attaching failure

Leon Hwang
2023-07-30T11:50:17Z

When error happens in dev_xdp_attach(), it should have a way to tell
users the error message like the netlink approach.

To avoid breaking uapi, adding a tracepoint in bpf_xdp_link_attach() is
an appropriate way to notify users the error message.

Hence, bpf libraries are able to retrieve the error message by this
tracepoint, and then report the error message to users.

Signed-off-by: Leon Hwang <hffilwlqm@gmail.com>
---
include/trace/events/xdp.h | 17 +++++++++++++++++
net/core/dev.c | 5 ++++-
2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h
index c40fc97f94171..cd89f1d5ce7b8 100644
--- a/include/trace/events/xdp.h
+++ b/include/trace/events/xdp.h
@@ -404,6 +404,23 @@ TRACE_EVENT(mem_return_failed,
)
);

+TRACE_EVENT(bpf_xdp_link_attach_failed,
+
+ TP_PROTO(const char *msg),
+
+ TP_ARGS(msg),
+
+ TP_STRUCT__entry(
+ __string(msg, msg)
+ ),
+
+ TP_fast_assign(
+ __assign_str(msg, msg);
+ ),
+
+ TP_printk("errmsg=%s", __get_str(msg))
+);
+
#endif /* _TRACE_XDP_H */

#include <trace/define_trace.h>
diff --git a/net/core/dev.c b/net/core/dev.c
index 8e7d0cb540cdb..49bed890f807e 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -133,6 +133,7 @@
#include <trace/events/net.h>
#include <trace/events/skb.h>
#include <trace/events/qdisc.h>
+#include <trace/events/xdp.h>
#include <linux/inetdevice.h>
#include <linux/cpu_rmap.h>
#include <linux/static_key.h>
@@ -9472,6 +9473,7 @@ int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
struct bpf_link_primer link_primer;
struct bpf_xdp_link *link;
struct net_device *dev;
+ struct netlink_ext_ack extack;
int err, fd;

rtnl_lock();
@@ -9497,12 +9499,13 @@ int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
goto unlock;
}

- err = dev_xdp_attach_link(dev, NULL, link);
+ err = dev_xdp_attach_link(dev, &extack, link);
rtnl_unlock();

if (err) {
link->dev = NULL;
bpf_link_cleanup(&link_primer);
+ trace_bpf_xdp_link_attach_failed(extack._msg);
goto out_put_dev;
}

--
2.41.0