2023-07-30 12:13:21

by Leon Hwang

Subject: [PATCH bpf-next v4 1/2] 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 <[email protected]>
---
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

2023-08-01 04:21:12

by Jakub Kicinski

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

On Sun, 30 Jul 2023 19:49:50 +0800 Leon Hwang wrote:
> @@ -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;

This is not initialized. Also, while fixing that, move it up
to maintain the line order by decreasing line length.

> 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);

2023-08-01 04:57:09

by Leon Hwang

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

On 1/8/23 10:43, Jakub Kicinski wrote:
> On Sun, 30 Jul 2023 19:49:50 +0800 Leon Hwang wrote:
>> @@ -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;
>
> This is not initialized. Also, while fixing that, move it up
> to maintain the line order by decreasing line length.
>

Thank you for your reviewing.

I'll fix it by initializing extack and moving the line to its appropriate position.

Thanks,
Leon

>> 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);