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Date: Sun, 7 Feb 2021 20:38:26 -0800
From: Yonghong Song <yhs@...com>
To: Song Liu <songliubraving@...com>, <bpf@...r.kernel.org>,
<netdev@...r.kernel.org>, <linux-mm@...ck.org>
CC: <ast@...nel.org>, <daniel@...earbox.net>, <kernel-team@...com>,
<akpm@...ux-foundation.org>
Subject: Re: [PATCH v4 bpf-next 4/4] selftests/bpf: add test for
bpf_iter_task_vma
On 2/4/21 12:50 PM, Song Liu wrote:
> The test dumps information similar to /proc/pid/maps. The first line of
> the output is compared against the /proc file to make sure they match.
>
> Signed-off-by: Song Liu <songliubraving@...com>
> ---
> .../selftests/bpf/prog_tests/bpf_iter.c | 114 ++++++++++++++++--
> tools/testing/selftests/bpf/progs/bpf_iter.h | 8 ++
> .../selftests/bpf/progs/bpf_iter_task_vma.c | 58 +++++++++
> 3 files changed, 170 insertions(+), 10 deletions(-)
> create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> index 0e586368948dd..9e8027685e859 100644
> --- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> @@ -7,6 +7,7 @@
> #include "bpf_iter_task.skel.h"
> #include "bpf_iter_task_stack.skel.h"
> #include "bpf_iter_task_file.skel.h"
> +#include "bpf_iter_task_vma.skel.h"
> #include "bpf_iter_task_btf.skel.h"
> #include "bpf_iter_tcp4.skel.h"
> #include "bpf_iter_tcp6.skel.h"
> @@ -64,6 +65,22 @@ static void do_dummy_read(struct bpf_program *prog)
> bpf_link__destroy(link);
> }
>
> +static int read_fd_into_buffer(int fd, char *buf, int size)
> +{
> + int bufleft = size;
> + int len;
> +
> + do {
> + len = read(fd, buf, bufleft);
> + if (len > 0) {
> + buf += len;
> + bufleft -= len;
> + }
> + } while (len > 0);
> +
> + return len < 0 ? len : size - bufleft;
> +}
> +
> static void test_ipv6_route(void)
> {
> struct bpf_iter_ipv6_route *skel;
> @@ -177,7 +194,7 @@ static int do_btf_read(struct bpf_iter_task_btf *skel)
> {
> struct bpf_program *prog = skel->progs.dump_task_struct;
> struct bpf_iter_task_btf__bss *bss = skel->bss;
> - int iter_fd = -1, len = 0, bufleft = TASKBUFSZ;
> + int iter_fd = -1, err;
> struct bpf_link *link;
> char *buf = taskbuf;
> int ret = 0;
> @@ -190,14 +207,7 @@ static int do_btf_read(struct bpf_iter_task_btf *skel)
> if (CHECK(iter_fd < 0, "create_iter", "create_iter failed\n"))
> goto free_link;
>
> - do {
> - len = read(iter_fd, buf, bufleft);
> - if (len > 0) {
> - buf += len;
> - bufleft -= len;
> - }
> - } while (len > 0);
> -
> + err = read_fd_into_buffer(iter_fd, buf, TASKBUFSZ);
> if (bss->skip) {
> printf("%s:SKIP:no __builtin_btf_type_id\n", __func__);
> ret = 1;
> @@ -205,7 +215,7 @@ static int do_btf_read(struct bpf_iter_task_btf *skel)
> goto free_link;
> }
>
> - if (CHECK(len < 0, "read", "read failed: %s\n", strerror(errno)))
> + if (CHECK(err < 0, "read", "read failed: %s\n", strerror(errno)))
> goto free_link;
>
> CHECK(strstr(taskbuf, "(struct task_struct)") == NULL,
> @@ -1133,6 +1143,88 @@ static void test_buf_neg_offset(void)
> bpf_iter_test_kern6__destroy(skel);
> }
>
> +#define CMP_BUFFER_SIZE 1024
> +static char task_vma_output[CMP_BUFFER_SIZE];
> +static char proc_maps_output[CMP_BUFFER_SIZE];
> +
> +/* remove \0 and \t from str, and only keep the first line */
> +static void str_strip_first_line(char *str)
> +{
> + char *dst = str, *src = str;
> +
> + do {
> + if (*src == ' ' || *src == '\t')
> + src++;
> + else
> + *(dst++) = *(src++);
> +
> + } while (*src != '\0' && *src != '\n');
> +
> + *dst = '\0';
> +}
> +
> +#define min(a, b) ((a) < (b) ? (a) : (b))
> +
> +static void test_task_vma(void)
> +{
> + int err, iter_fd = -1, proc_maps_fd = -1;
> + struct bpf_iter_task_vma *skel;
> + int len, read_size = 4;
> + char maps_path[64];
> +
> + skel = bpf_iter_task_vma__open();
> + if (CHECK(!skel, "bpf_iter_task_vma__open", "skeleton open failed\n"))
> + return;
> +
> + skel->bss->pid = getpid();
> +
> + err = bpf_iter_task_vma__load(skel);
> + if (CHECK(err, "bpf_iter_task_vma__load", "skeleton load failed\n"))
> + goto out;
> +
> + skel->links.proc_maps = bpf_program__attach_iter(
> + skel->progs.proc_maps, NULL);
> +
> + if (CHECK(IS_ERR(skel->links.proc_maps), "bpf_program__attach_iter",
> + "attach iterator failed\n"))
> + goto out;
You need to set skel->links.proc_maps = NULL before goto out. Otherwise,
libbpf may segfault.
> +
> + /* read CMP_BUFFER_SIZE (1kB) from bpf_iter */
This comment better right before
/* read in small chunks to trigger seq_file corner cases */
> + iter_fd = bpf_iter_create(bpf_link__fd(skel->links.proc_maps));
> + if (CHECK(iter_fd < 0, "create_iter", "create_iter failed\n"))
> + goto out;
> +
> + /* read in small chunks to trigger seq_file corner cases */
> + len = 0;
> + while (len < CMP_BUFFER_SIZE) {
Some comment will be better to assure that we won't trigger infinite
loop here, e.g., err == 0 case.
> + err = read_fd_into_buffer(iter_fd, task_vma_output + len,
> + min(read_size, CMP_BUFFER_SIZE - len));
> + if (CHECK(err < 0, "read_iter_fd", "read_iter_fd failed\n"))
> + goto out;
> + len += err;
> + }
> +
> + /* read CMP_BUFFER_SIZE (1kB) from /proc/pid/maps */
> + snprintf(maps_path, 64, "/proc/%u/maps", skel->bss->pid);
> + proc_maps_fd = open(maps_path, O_RDONLY);
> + if (CHECK(proc_maps_fd < 0, "open_proc_maps", "open_proc_maps failed\n"))
> + goto out;
> + err = read_fd_into_buffer(proc_maps_fd, proc_maps_output, CMP_BUFFER_SIZE);
> + if (CHECK(err < 0, "read_prog_maps_fd", "read_prog_maps_fd failed\n"))
> + goto out;
> +
> + /* strip and compare the first line of the two files */
> + str_strip_first_line(task_vma_output);
> + str_strip_first_line(proc_maps_output);
> +
> + CHECK(strcmp(task_vma_output, proc_maps_output), "compare_output",
> + "found mismatch\n");
> +out:
> + close(proc_maps_fd);
> + close(iter_fd);
> + bpf_iter_task_vma__destroy(skel);
> +}
> +
> void test_bpf_iter(void)
> {
> if (test__start_subtest("btf_id_or_null"))
> @@ -1149,6 +1241,8 @@ void test_bpf_iter(void)
> test_task_stack();
> if (test__start_subtest("task_file"))
> test_task_file();
> + if (test__start_subtest("task_vma"))
> + test_task_vma();
> if (test__start_subtest("task_btf"))
> test_task_btf();
> if (test__start_subtest("tcp4"))
> diff --git a/tools/testing/selftests/bpf/progs/bpf_iter.h b/tools/testing/selftests/bpf/progs/bpf_iter.h
> index 6a1255465fd6d..3d83b185c4bcb 100644
> --- a/tools/testing/selftests/bpf/progs/bpf_iter.h
> +++ b/tools/testing/selftests/bpf/progs/bpf_iter.h
[...]
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