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SubjectRe: [PATCH v3 bpf-next 4/4] selftests/bpf: add bpf_iter test with bpf_get_task_stack()
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On 6/26/20 5:26 PM, Song Liu wrote:
> The new test is similar to other bpf_iter tests.

It would be great if you can show some results from
bpf_iter_task_stack.c dump.

>
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
> .../selftests/bpf/prog_tests/bpf_iter.c | 17 ++++++
> .../selftests/bpf/progs/bpf_iter_task_stack.c | 53 +++++++++++++++++++
> 2 files changed, 70 insertions(+)
> create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> index 1e2e0fced6e81..fed42755416db 100644
> --- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> @@ -5,6 +5,7 @@
> #include "bpf_iter_netlink.skel.h"
> #include "bpf_iter_bpf_map.skel.h"
> #include "bpf_iter_task.skel.h"
> +#include "bpf_iter_task_stack.skel.h"
> #include "bpf_iter_task_file.skel.h"
> #include "bpf_iter_tcp4.skel.h"
> #include "bpf_iter_tcp6.skel.h"
> @@ -110,6 +111,20 @@ static void test_task(void)
> bpf_iter_task__destroy(skel);
> }
>
> +static void test_task_stack(void)
> +{
> + struct bpf_iter_task_stack *skel;
> +
> + skel = bpf_iter_task_stack__open_and_load();
> + if (CHECK(!skel, "bpf_iter_task_stack__open_and_load",
> + "skeleton open_and_load failed\n"))
> + return;
> +
> + do_dummy_read(skel->progs.dump_task_stack);
> +
> + bpf_iter_task_stack__destroy(skel);
> +}
> +
> static void test_task_file(void)
> {
> struct bpf_iter_task_file *skel;
> @@ -452,6 +467,8 @@ void test_bpf_iter(void)
> test_bpf_map();
> if (test__start_subtest("task"))
> test_task();
> + if (test__start_subtest("task_stack"))
> + test_task_stack();
> if (test__start_subtest("task_file"))
> test_task_file();
> if (test__start_subtest("tcp4"))
> diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c b/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c
> new file mode 100644
> index 0000000000000..39b21df17c3ee
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c
> @@ -0,0 +1,53 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2020 Facebook */
> +/* "undefine" structs in vmlinux.h, because we "override" them below */
> +#define bpf_iter_meta bpf_iter_meta___not_used
> +#define bpf_iter__task bpf_iter__task___not_used
> +#include "vmlinux.h"
> +#undef bpf_iter_meta
> +#undef bpf_iter__task
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +char _license[] SEC("license") = "GPL";
> +
> +struct bpf_iter_meta {
> + struct seq_file *seq;
> + __u64 session_id;
> + __u64 seq_num;
> +} __attribute__((preserve_access_index));
> +
> +struct bpf_iter__task {
> + struct bpf_iter_meta *meta;
> + struct task_struct *task;
> +} __attribute__((preserve_access_index));

Please take a look at bpf_iter_task.c. The above code can be simplified as
#include "bpf_iter.h"
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>

> +
> +#define MAX_STACK_TRACE_DEPTH 64
> +unsigned long entries[MAX_STACK_TRACE_DEPTH];
> +#define SIZE_OF_ULONG (sizeof(unsigned long))
> +
> +SEC("iter/task")
> +int dump_task_stack(struct bpf_iter__task *ctx)
> +{
> + struct seq_file *seq = ctx->meta->seq;
> + struct task_struct *task = ctx->task;
> + long i, retlen;
> +
> + if (task == (void *)0)
> + return 0;
> +
> + retlen = bpf_get_task_stack(task, entries,
> + MAX_STACK_TRACE_DEPTH * SIZE_OF_ULONG, 0);
> + if (retlen < 0)
> + return 0;
> +
> + BPF_SEQ_PRINTF(seq, "pid: %8u num_entries: %8u\n", task->pid,
> + retlen / SIZE_OF_ULONG);
> + for (i = 0; i < MAX_STACK_TRACE_DEPTH; i++) {
> + if (retlen > i * SIZE_OF_ULONG)
> + BPF_SEQ_PRINTF(seq, "[<0>] %pB\n", (void *)entries[i]);
> + }
> + BPF_SEQ_PRINTF(seq, "\n");
> +
> + return 0;
> +}
>

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