[RFC PATCH bpf-next 15/16] tools/bpf: selftests: add dumper progs for bpf_map/task/task_file

[Yonghong Song <yhs@fb.com>]

The implementation is arbitrary, just to show how the bpf programs
can be written for bpf_map/task/task_file. They can be costomized
for specific needs.

For example, for bpf_map, the dumper prints out:
  $ cat /sys/kernel/bpfdump/bpf_map/my1
      id   refcnt  usercnt  locked_vm
       3        2        0         20
       6        2        0         20
       9        2        0         20
      12        2        0         20
      13        2        0         20
      16        2        0         20
      19        2        0         20

For task, the dumper prints out:
  $ cat /sys/kernel/bpfdump/task/my1
    tgid      gid
       1        1
       2        2
    ....
    1944     1944
    1948     1948
    1949     1949
    1953     1953

For task/file, the dumper prints out:
  $ cat /sys/kernel/bpfdump/task/file/my1
    tgid      gid       fd      file
       1        1        0 ffffffff95c97600
       1        1        1 ffffffff95c97600
       1        1        2 ffffffff95c97600
    ....
    1895     1895      255 ffffffff95c8fe00
    1932     1932        0 ffffffff95c8fe00
    1932     1932        1 ffffffff95c8fe00
    1932     1932        2 ffffffff95c8fe00
    1932     1932        3 ffffffff95c185c0

This is able to print out all open files (fd and file->f_op), so user can compare
f_op against a particular kernel file operations to find what it is.
For example, from /proc/kallsyms, we can find
  ffffffff95c185c0 r eventfd_fops
so we will know tgid 1932 fd 3 is an eventfd file descriptor.

Signed-off-by: Yonghong Song <yhs@fb.com>
---
 .../selftests/bpf/progs/bpfdump_bpf_map.c     | 24 +++++++++++++++++++
 .../selftests/bpf/progs/bpfdump_task.c        | 21 ++++++++++++++++
 .../selftests/bpf/progs/bpfdump_task_file.c   | 24 +++++++++++++++++++
 3 files changed, 69 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/bpfdump_bpf_map.c
 create mode 100644 tools/testing/selftests/bpf/progs/bpfdump_task.c
 create mode 100644 tools/testing/selftests/bpf/progs/bpfdump_task_file.c

diff --git a/tools/testing/selftests/bpf/progs/bpfdump_bpf_map.c b/tools/testing/selftests/bpf/progs/bpfdump_bpf_map.c
new file mode 100644
index 000000000000..c85f5a330010
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpfdump_bpf_map.c
@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_endian.h>
+
+char _license[] SEC("license") = "GPL";
+
+SEC("dump//sys/kernel/bpfdump/bpf_map")
+int BPF_PROG(dump_bpf_map, struct bpf_map *map, struct seq_file *seq, u64 seq_num)
+{
+	static const char banner[] = "      id   refcnt  usercnt  locked_vm\n";
+	static const char fmt1[] = "%8u %8ld ";
+	static const char fmt2[] = "%8ld %10lu\n";
+
+	if (seq_num == 0)
+		bpf_seq_printf(seq, banner, sizeof(banner));
+
+	bpf_seq_printf(seq, fmt1, sizeof(fmt1), map->id, map->refcnt.counter);
+	bpf_seq_printf(seq, fmt2, sizeof(fmt2), map->usercnt.counter,
+		       map->memory.user->locked_vm.counter);
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/bpfdump_task.c b/tools/testing/selftests/bpf/progs/bpfdump_task.c
new file mode 100644
index 000000000000..4d90ba97fbda
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpfdump_task.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_endian.h>
+
+char _license[] SEC("license") = "GPL";
+
+SEC("dump//sys/kernel/bpfdump/task")
+int BPF_PROG(dump_tasks, struct task_struct *task, struct seq_file *seq, u64 seq_num)
+{
+	static char const banner[] = "    tgid      gid\n";
+	static char const fmt[] = "%8d %8d\n";
+
+	if (seq_num == 0)
+		bpf_seq_printf(seq, banner, sizeof(banner));
+
+	bpf_seq_printf(seq, fmt, sizeof(fmt), task->tgid, task->pid);
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/bpfdump_task_file.c b/tools/testing/selftests/bpf/progs/bpfdump_task_file.c
new file mode 100644
index 000000000000..5cf02c050e1f
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpfdump_task_file.c
@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_endian.h>
+
+char _license[] SEC("license") = "GPL";
+
+SEC("dump//sys/kernel/bpfdump/task/file")
+int BPF_PROG(dump_tasks, struct task_struct *task, __u32 fd, struct file *file,
+	     struct seq_file *seq, u64 seq_num)
+{
+	static char const banner[] = "    tgid      gid       fd      file\n";
+	static char const fmt1[] = "%8d %8d";
+	static char const fmt2[] = " %8d %lx\n";
+
+	if (seq_num == 0)
+		bpf_seq_printf(seq, banner, sizeof(banner));
+
+	bpf_seq_printf(seq, fmt1, sizeof(fmt1), task->tgid, task->pid);
+	bpf_seq_printf(seq, fmt2, sizeof(fmt2), fd, (long)file->f_op);
+	return 0;
+}
-- 
2.24.1