Re: [PATCH bpf-next v8 4/5] selftests/bpf: Test parameterized task BPF iterators.

[Yonghong Song <yhs@fb.com>]

On 8/29/22 12:23 PM, Kui-Feng Lee wrote:
> Test iterators of vma, files and tasks.
> 
> Ensure the API works appropriately to visit all tasks,
> tasks in a process, or a particular task.
> 
> Signed-off-by: Kui-Feng Lee <kuifeng@fb.com>
> ---
>   .../selftests/bpf/prog_tests/bpf_iter.c       | 282 ++++++++++++++++--
>   .../selftests/bpf/prog_tests/btf_dump.c       |   2 +-
>   .../selftests/bpf/progs/bpf_iter_task.c       |   9 +
>   .../selftests/bpf/progs/bpf_iter_task_file.c  |   9 +-
>   .../selftests/bpf/progs/bpf_iter_task_vma.c   |   7 +-
>   .../selftests/bpf/progs/bpf_iter_vma_offset.c |  37 +++
>   6 files changed, 322 insertions(+), 24 deletions(-)
>   create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_vma_offset.c
> 
[...]
> +
> +static void test_task_vma_offset_common(struct bpf_iter_attach_opts *opts, bool one_proc)
> +{
> +	struct bpf_iter_vma_offset *skel;
> +	struct bpf_link *link;
> +	char buf[16] = {};
> +	int iter_fd, len;
> +	int pgsz, shift;
> +
> +	skel = bpf_iter_vma_offset__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "bpf_iter_vma_offset__open_and_load"))
> +		return;
> +
> +	skel->bss->pid = getpid();
> +	skel->bss->address = (uintptr_t)trigger_func;
> +	for (pgsz = getpagesize(), shift = 0; pgsz; pgsz >>= 1, shift++)
> +		;
> +	skel->bss->page_shift = shift;

if getpagesize() is 4K, shift will be 13 which is incorrect.

> +
> +	link = bpf_program__attach_iter(skel->progs.get_vma_offset, opts);
> +	if (!ASSERT_OK_PTR(link, "attach_iter"))
> +		return;
> +
> +	iter_fd = bpf_iter_create(bpf_link__fd(link));
> +	if (!ASSERT_GT(iter_fd, 0, "create_iter"))
> +		goto exit;
> +
> +	while ((len = read(iter_fd, buf, sizeof(buf))) > 0)
> +		;
> +	buf[15] = 0;
> +	ASSERT_EQ(strcmp(buf, "OK\n"), 0, "strcmp");
> +
> +	ASSERT_EQ(skel->bss->offset, get_uprobe_offset(trigger_func), "offset");
> +	if (one_proc)
> +		ASSERT_EQ(skel->bss->unique_tgid_cnt, 1, "unique_tgid_count");
> +	else
> +		ASSERT_GT(skel->bss->unique_tgid_cnt, 1, "unique_tgid_count");
> +
> +	close(iter_fd);
> +
> +exit:
> +	bpf_link__destroy(link);
> +}
> +
> +static void test_task_vma_offset(void)
> +{
> +	LIBBPF_OPTS(bpf_iter_attach_opts, opts);
> +	union bpf_iter_link_info linfo;
> +
> +	memset(&linfo, 0, sizeof(linfo));
> +	linfo.task.pid = getpid();
> +	opts.link_info = &linfo;
> +	opts.link_info_len = sizeof(linfo);
> +
> +	test_task_vma_offset_common(&opts, true);
> +
> +	linfo.task.pid = 0;
> +	linfo.task.tid = getpid();
> +	test_task_vma_offset_common(&opts, true);
> +
> +	test_task_vma_offset_common(NULL, false);
> +}
> +
>   void test_bpf_iter(void)
>   {
> +	ASSERT_OK(pthread_mutex_init(&do_nothing_mutex, NULL), "pthread_mutex_init");
> +
>   	if (test__start_subtest("btf_id_or_null"))
>   		test_btf_id_or_null();
>   	if (test__start_subtest("ipv6_route"))
> @@ -1335,8 +1569,12 @@ void test_bpf_iter(void)
>   		test_netlink();
>   	if (test__start_subtest("bpf_map"))
>   		test_bpf_map();
> -	if (test__start_subtest("task"))
> -		test_task();
> +	if (test__start_subtest("task_tid"))
> +		test_task_tid();
> +	if (test__start_subtest("task_pid"))
> +		test_task_pid();
> +	if (test__start_subtest("task_pidfd"))
> +		test_task_pidfd();
>   	if (test__start_subtest("task_sleepable"))
>   		test_task_sleepable();
>   	if (test__start_subtest("task_stack"))
> @@ -1397,4 +1635,6 @@ void test_bpf_iter(void)
>   		test_ksym_iter();
>   	if (test__start_subtest("bpf_sockmap_map_iter_fd"))
>   		test_bpf_sockmap_map_iter_fd();
> +	if (test__start_subtest("vma_offset"))
> +		test_task_vma_offset();
>   }
[...]
> diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_vma_offset.c b/tools/testing/selftests/bpf/progs/bpf_iter_vma_offset.c
> new file mode 100644
> index 000000000000..03db36da5da8
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/bpf_iter_vma_offset.c
> @@ -0,0 +1,37 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
> +#include "bpf_iter.h"
> +#include <bpf/bpf_helpers.h>
> +
> +char _license[] SEC("license") = "GPL";
> +
> +__u32 unique_tgid_cnt = 0;
> +uintptr_t address = 0;
> +uintptr_t offset = 0;
> +__u32 last_tgid = 0;
> +__u32 pid = 0;
> +__u32 page_shift = 0;

page_shift is not used here.

> +
> +SEC("iter/task_vma")
> +int get_vma_offset(struct bpf_iter__task_vma *ctx)
> +{
> +	struct vm_area_struct *vma = ctx->vma;
> +	struct seq_file *seq = ctx->meta->seq;
> +	struct task_struct *task = ctx->task;
> +
> +	if (task == NULL || vma == NULL)
> +		return 0;
> +
> +	if (last_tgid != task->tgid)
> +		unique_tgid_cnt++;
> +	last_tgid = task->tgid;
> +
> +	if (task->tgid != pid)
> +		return 0;
> +
> +	if (vma->vm_start <= address && vma->vm_end > address) {
> +		offset = address - vma->vm_start + (vma->vm_pgoff << 12);

'12' -> page_shift?

> +		BPF_SEQ_PRINTF(seq, "OK\n");
> +	}
> +	return 0;
> +}