This series introduces a new tracepoint in bpf_xdp_link_attach(). By
this tracepoint, error message will be captured when error happens in
dev_xdp_attach(), e.g. invalid attaching flags.
v4 -> v5:
* Initialise the extack variable.
* Fix code style issue of variable declaration lines.
v3 -> v4:
* Fix selftest-crashed issue.
Leon Hwang (2):
bpf, xdp: add tracepoint to xdp attaching failure
selftests/bpf: Add testcase for xdp attaching failure tracepoint
include/trace/events/xdp.h | 17 +++++
net/core/dev.c | 5 +-
.../selftests/bpf/prog_tests/xdp_attach.c | 65 +++++++++++++++++++
.../bpf/progs/test_xdp_attach_fail.c | 54 +++++++++++++++
4 files changed, 140 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/bpf/progs/test_xdp_attach_fail.c
base-commit: a33d978500acd8fb67efac9773ba0a8502c1ff06
--
2.41.0
Add a test case for the tracepoint of xdp attaching failure by bpf
tracepoint when attach XDP to a device with invalid flags option.
The bpf tracepoint retrieves error message from the tracepoint, and
then put the error message to a perf buffer. The testing code receives
error message from perf buffer, and then ASSERT "Invalid XDP flags for
BPF link attachment".
Signed-off-by: Leon Hwang <[email protected]>
---
.../selftests/bpf/prog_tests/xdp_attach.c | 65 +++++++++++++++++++
.../bpf/progs/test_xdp_attach_fail.c | 54 +++++++++++++++
2 files changed, 119 insertions(+)
create mode 100644 tools/testing/selftests/bpf/progs/test_xdp_attach_fail.c
diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_attach.c b/tools/testing/selftests/bpf/prog_tests/xdp_attach.c
index fa3cac5488f5d..e6bcb6051402d 100644
--- a/tools/testing/selftests/bpf/prog_tests/xdp_attach.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_attach.c
@@ -1,5 +1,6 @@
// SPDX-License-Identifier: GPL-2.0
#include <test_progs.h>
+#include "test_xdp_attach_fail.skel.h"
#define IFINDEX_LO 1
#define XDP_FLAGS_REPLACE (1U << 4)
@@ -85,10 +86,74 @@ static void test_xdp_attach(const char *file)
bpf_object__close(obj1);
}
+#define ERRMSG_LEN 64
+
+struct xdp_errmsg {
+ char msg[ERRMSG_LEN];
+};
+
+static void on_xdp_errmsg(void *ctx, int cpu, void *data, __u32 size)
+{
+ struct xdp_errmsg *ctx_errmg = ctx, *tp_errmsg = data;
+
+ memcpy(&ctx_errmg->msg, &tp_errmsg->msg, ERRMSG_LEN);
+}
+
+static const char tgt_errmsg[] = "Invalid XDP flags for BPF link attachment";
+
+static void test_xdp_attach_fail(const char *file)
+{
+ struct test_xdp_attach_fail *skel = NULL;
+ struct xdp_errmsg errmsg = {};
+ struct perf_buffer *pb = NULL;
+ struct bpf_object *obj = NULL;
+ int err, fd_xdp;
+
+ LIBBPF_OPTS(bpf_link_create_opts, opts);
+
+ skel = test_xdp_attach_fail__open_and_load();
+ if (!ASSERT_OK_PTR(skel, "test_xdp_attach_fail__open_and_load"))
+ goto out_close;
+
+ err = test_xdp_attach_fail__attach(skel);
+ if (!ASSERT_EQ(err, 0, "test_xdp_attach_fail__attach"))
+ goto out_close;
+
+ /* set up perf buffer */
+ pb = perf_buffer__new(bpf_map__fd(skel->maps.xdp_errmsg_pb), 1,
+ on_xdp_errmsg, NULL, &errmsg, NULL);
+ if (!ASSERT_OK_PTR(pb, "perf_buffer__new"))
+ goto out_close;
+
+ err = bpf_prog_test_load(file, BPF_PROG_TYPE_XDP, &obj, &fd_xdp);
+ if (!ASSERT_EQ(err, 0, "bpf_prog_test_load"))
+ goto out_close;
+
+ opts.flags = 0xFF; // invalid flags to fail to attach XDP prog
+ err = bpf_link_create(fd_xdp, IFINDEX_LO, BPF_XDP, &opts);
+ if (!ASSERT_EQ(err, -EINVAL, "bpf_link_create"))
+ goto out_close;
+
+ /* read perf buffer */
+ err = perf_buffer__poll(pb, 100);
+ if (!ASSERT_GT(err, -1, "perf_buffer__poll"))
+ goto out_close;
+
+ ASSERT_STRNEQ((const char *) errmsg.msg, tgt_errmsg,
+ 42 /* strlen(tgt_errmsg) */, "check error message");
+
+out_close:
+ perf_buffer__free(pb);
+ bpf_object__close(obj);
+ test_xdp_attach_fail__destroy(skel);
+}
+
void serial_test_xdp_attach(void)
{
if (test__start_subtest("xdp_attach"))
test_xdp_attach("./test_xdp.bpf.o");
if (test__start_subtest("xdp_attach_dynptr"))
test_xdp_attach("./test_xdp_dynptr.bpf.o");
+ if (test__start_subtest("xdp_attach_failed"))
+ test_xdp_attach_fail("./xdp_dummy.bpf.o");
}
diff --git a/tools/testing/selftests/bpf/progs/test_xdp_attach_fail.c b/tools/testing/selftests/bpf/progs/test_xdp_attach_fail.c
new file mode 100644
index 0000000000000..2ff1b596e87ea
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_xdp_attach_fail.c
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright Leon Hwang */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+#define ERRMSG_LEN 64
+
+struct xdp_errmsg {
+ char msg[ERRMSG_LEN];
+};
+
+struct {
+ __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
+ __type(key, int);
+ __type(value, int);
+} xdp_errmsg_pb SEC(".maps");
+
+struct xdp_attach_error_ctx {
+ unsigned long unused;
+
+ /*
+ * bpf does not support tracepoint __data_loc directly.
+ *
+ * Actually, this field is a 32 bit integer whose value encodes
+ * information on where to find the actual data. The first 2 bytes is
+ * the size of the data. The last 2 bytes is the offset from the start
+ * of the tracepoint struct where the data begins.
+ * -- https://github.com/iovisor/bpftrace/pull/1542
+ */
+ __u32 msg; // __data_loc char[] msg;
+};
+
+/*
+ * Catch the error message at the tracepoint.
+ */
+
+SEC("tp/xdp/bpf_xdp_link_attach_failed")
+int tp__xdp__bpf_xdp_link_attach_failed(struct xdp_attach_error_ctx *ctx)
+{
+ char *msg = (void *)(__u64) ((void *) ctx + (__u16) ctx->msg);
+ struct xdp_errmsg errmsg = {};
+
+ bpf_probe_read_kernel_str(&errmsg.msg, ERRMSG_LEN, msg);
+ bpf_perf_event_output(ctx, &xdp_errmsg_pb, BPF_F_CURRENT_CPU, &errmsg,
+ ERRMSG_LEN);
+ return 0;
+}
+
+/*
+ * Reuse the XDP program in xdp_dummy.c.
+ */
+
+char LICENSE[] SEC("license") = "GPL";
--
2.41.0
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..002fec07de739 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>
@@ -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;
}
--
2.41.0
On Tue, 1 Aug 2023 22:26:20 +0800 Leon Hwang wrote:
> 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.
Whatevered-by: Jakub Kicinski <[email protected]> ?
On 2/8/23 06:08, Jakub Kicinski wrote:
> On Tue, 1 Aug 2023 22:26:20 +0800 Leon Hwang wrote:
>> 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.
>
> Whatevered-by: Jakub Kicinski <[email protected]> ?
Oh, it's not responsible for libraries to retrieve the error message. It
should be users' responsibility.
Sorry for the misguiding text.
In the previous patch[0], which changes uapi, it's able to back-propagate
the error message from dev_xdp_attach() to userspace through BPF syscall.
Then, tracepoint idea is suggested to avoid changing uapi. I do agree to
implement a tracepoint to avoid changing uapi.
[0] bpf: Introduce user log
https://lore.kernel.org/bpf/[email protected]/
Thanks,
Leon
Hello:
This series was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <[email protected]>:
On Tue, 1 Aug 2023 22:26:19 +0800 you wrote:
> This series introduces a new tracepoint in bpf_xdp_link_attach(). By
> this tracepoint, error message will be captured when error happens in
> dev_xdp_attach(), e.g. invalid attaching flags.
>
> v4 -> v5:
> * Initialise the extack variable.
> * Fix code style issue of variable declaration lines.
>
> [...]
Here is the summary with links:
- [bpf-next,v5,1/2] bpf, xdp: Add tracepoint to xdp attaching failure
https://git.kernel.org/bpf/bpf-next/c/bf4ea1d0b2cb
- [bpf-next,v5,2/2] selftests/bpf: Add testcase for xdp attaching failure tracepoint
https://git.kernel.org/bpf/bpf-next/c/7fedbf32fcc7
You are awesome, thank you!
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