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
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..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; }
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 kuba@kernel.org ?
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 kuba@kernel.org ?
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/20230708040750.72570-1-hffilwlqm@gmail.com/
Thanks, Leon
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 hffilwlqm@gmail.com --- .../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";
Hello:
This series was applied to bpf/bpf-next.git (master) by Alexei Starovoitov ast@kernel.org:
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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