bpf, xdp: Add tracepoint to xdp attaching failure

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>
Link: https://lore.kernel.org/r/20230801142621.7925-2-hffilwlqm@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h
index c40fc97..cd89f1d 100644 (file)
--- 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 8e7d0cb..002fec0 100644 (file)
--- 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>
@@ -9470,6 +9471,7 @@ int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 {
        struct net *net = current->nsproxy->net_ns;
        struct bpf_link_primer link_primer;
+       struct netlink_ext_ack extack = {};
        struct bpf_xdp_link *link;
        struct net_device *dev;
        int err, fd;
@@ -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;
        }