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Subject[PATCH v6 bpf-next 6/6] selftests/bpf: add test for bpf_seq_printf_btf helper
Date
Add a test verifying iterating over tasks and displaying BTF
representation of data succeeds. Note here that we do not display
the task_struct itself, as it will overflow the PAGE_SIZE limit on seq
data; instead we write task->fs (a struct fs_struct).

Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
tools/testing/selftests/bpf/prog_tests/bpf_iter.c | 66 ++++++++++++++++++++++
.../selftests/bpf/progs/bpf_iter_task_btf.c | 49 ++++++++++++++++
2 files changed, 115 insertions(+)
create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_task_btf.c

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
index fe1a83b9..323c48a 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_btf.skel.h"
#include "bpf_iter_tcp4.skel.h"
#include "bpf_iter_tcp6.skel.h"
#include "bpf_iter_udp4.skel.h"
@@ -167,6 +168,69 @@ static void test_task_file(void)
bpf_iter_task_file__destroy(skel);
}

+#define FSBUFSZ 8192
+
+static char fsbuf[FSBUFSZ];
+
+static void do_btf_read(struct bpf_program *prog)
+{
+ int iter_fd = -1, len = 0, bufleft = FSBUFSZ;
+ struct bpf_link *link;
+ char *buf = fsbuf;
+
+ link = bpf_program__attach_iter(prog, NULL);
+ if (CHECK(IS_ERR(link), "attach_iter", "attach_iter failed\n"))
+ return;
+
+ iter_fd = bpf_iter_create(bpf_link__fd(link));
+ 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);
+
+ if (CHECK(len < 0, "read", "read failed: %s\n", strerror(errno)))
+ goto free_link;
+
+ CHECK(strstr(fsbuf, "(struct fs_struct)") == NULL,
+ "check for btf representation of fs_struct in iter data",
+ "struct fs_struct not found");
+free_link:
+ if (iter_fd > 0)
+ close(iter_fd);
+ bpf_link__destroy(link);
+}
+
+static void test_task_btf(void)
+{
+ struct bpf_iter_task_btf__bss *bss;
+ struct bpf_iter_task_btf *skel;
+
+ skel = bpf_iter_task_btf__open_and_load();
+ if (CHECK(!skel, "bpf_iter_task_btf__open_and_load",
+ "skeleton open_and_load failed\n"))
+ return;
+
+ bss = skel->bss;
+
+ do_btf_read(skel->progs.dump_task_fs_struct);
+
+ if (CHECK(bss->tasks == 0, "check if iterated over tasks",
+ "no task iteration, did BPF program run?\n"))
+ goto cleanup;
+
+ CHECK(bss->seq_err != 0, "check for unexpected err",
+ "bpf_seq_printf_btf returned %ld", bss->seq_err);
+
+cleanup:
+ bpf_iter_task_btf__destroy(skel);
+}
+
static void test_tcp4(void)
{
struct bpf_iter_tcp4 *skel;
@@ -957,6 +1021,8 @@ void test_bpf_iter(void)
test_task_stack();
if (test__start_subtest("task_file"))
test_task_file();
+ if (test__start_subtest("task_btf"))
+ test_task_btf();
if (test__start_subtest("tcp4"))
test_tcp4();
if (test__start_subtest("tcp6"))
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_task_btf.c b/tools/testing/selftests/bpf/progs/bpf_iter_task_btf.c
new file mode 100644
index 0000000..88631a8
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_task_btf.c
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020, Oracle and/or its affiliates. */
+#include "bpf_iter.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include <errno.h>
+
+char _license[] SEC("license") = "GPL";
+
+long tasks = 0;
+long seq_err = 0;
+
+/* struct task_struct's BTF representation will overflow PAGE_SIZE so cannot
+ * be used here; instead dump a structure associated with each task.
+ */
+SEC("iter/task")
+int dump_task_fs_struct(struct bpf_iter__task *ctx)
+{
+ static const char fs_type[] = "struct fs_struct";
+ struct seq_file *seq = ctx->meta->seq;
+ struct task_struct *task = ctx->task;
+ struct fs_struct *fs = (void *)0;
+ static struct btf_ptr ptr = { };
+ long ret;
+
+ if (task)
+ fs = task->fs;
+
+ ptr.type = fs_type;
+ ptr.ptr = fs;
+
+ if (ctx->meta->seq_num == 0)
+ BPF_SEQ_PRINTF(seq, "Raw BTF fs_struct per task\n");
+
+ ret = bpf_seq_printf_btf(seq, &ptr, sizeof(ptr), 0);
+ switch (ret) {
+ case 0:
+ tasks++;
+ break;
+ case -ERANGE:
+ /* NULL task or task->fs, don't count it as an error. */
+ break;
+ default:
+ seq_err = ret;
+ break;
+ }
+
+ return 0;
+}
--
1.8.3.1
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