bpf: Add BPF program and map iterators as built-in BPF programs.

The program and map iterators work similar to seq_file-s.
Once the program is pinned in bpffs it can be read with "cat" tool
to print human readable output. In this case about BPF programs and maps.
For example:
$ cat /sys/fs/bpf/progs.debug
  id name            attached
   5 dump_bpf_map    bpf_iter_bpf_map
   6 dump_bpf_prog   bpf_iter_bpf_prog
$ cat /sys/fs/bpf/maps.debug
  id name            max_entries
   3 iterator.rodata     1

To avoid kernel build dependency on clang 10 separate bpf skeleton generation
into manual "make" step and instead check-in generated .skel.h into git.

Unlike 'bpftool prog show' in-kernel BTF name is used (when available)
to print full name of BPF program instead of 16-byte truncated name.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200819042759.51280-3-alexei.starovoitov@gmail.com

1 files changed, 114 insertions, 0 deletions

diff --git a/kernel/bpf/preload/iterators/iterators.bpf.c b/kernel/bpf/preload/iterators/iterators.bpf.c
new file mode 100644
index 000000000000..5ded550b2ed6
--- /dev/null
+++ b/kernel/bpf/preload/iterators/iterators.bpf.c
@@ -0,0 +1,114 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_core_read.h>
+
+#pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)
+struct seq_file;
+struct bpf_iter_meta {
+	struct seq_file *seq;
+	__u64 session_id;
+	__u64 seq_num;
+};
+
+struct bpf_map {
+	__u32 id;
+	char name[16];
+	__u32 max_entries;
+};
+
+struct bpf_iter__bpf_map {
+	struct bpf_iter_meta *meta;
+	struct bpf_map *map;
+};
+
+struct btf_type {
+	__u32 name_off;
+};
+
+struct btf_header {
+	__u32   str_len;
+};
+
+struct btf {
+	const char *strings;
+	struct btf_type **types;
+	struct btf_header hdr;
+};
+
+struct bpf_prog_aux {
+	__u32 id;
+	char name[16];
+	const char *attach_func_name;
+	struct bpf_prog *linked_prog;
+	struct bpf_func_info *func_info;
+	struct btf *btf;
+};
+
+struct bpf_prog {
+	struct bpf_prog_aux *aux;
+};
+
+struct bpf_iter__bpf_prog {
+	struct bpf_iter_meta *meta;
+	struct bpf_prog *prog;
+};
+#pragma clang attribute pop
+
+static const char *get_name(struct btf *btf, long btf_id, const char *fallback)
+{
+	struct btf_type **types, *t;
+	unsigned int name_off;
+	const char *str;
+
+	if (!btf)
+		return fallback;
+	str = btf->strings;
+	types = btf->types;
+	bpf_probe_read_kernel(&t, sizeof(t), types + btf_id);
+	name_off = BPF_CORE_READ(t, name_off);
+	if (name_off >= btf->hdr.str_len)
+		return fallback;
+	return str + name_off;
+}
+
+SEC("iter/bpf_map")
+int dump_bpf_map(struct bpf_iter__bpf_map *ctx)
+{
+	struct seq_file *seq = ctx->meta->seq;
+	__u64 seq_num = ctx->meta->seq_num;
+	struct bpf_map *map = ctx->map;
+
+	if (!map)
+		return 0;
+
+	if (seq_num == 0)
+		BPF_SEQ_PRINTF(seq, "  id name             max_entries\n");
+
+	BPF_SEQ_PRINTF(seq, "%4u %-16s%6d\n", map->id, map->name, map->max_entries);
+	return 0;
+}
+
+SEC("iter/bpf_prog")
+int dump_bpf_prog(struct bpf_iter__bpf_prog *ctx)
+{
+	struct seq_file *seq = ctx->meta->seq;
+	__u64 seq_num = ctx->meta->seq_num;
+	struct bpf_prog *prog = ctx->prog;
+	struct bpf_prog_aux *aux;
+
+	if (!prog)
+		return 0;
+
+	aux = prog->aux;
+	if (seq_num == 0)
+		BPF_SEQ_PRINTF(seq, "  id name             attached\n");
+
+	BPF_SEQ_PRINTF(seq, "%4u %-16s %s %s\n", aux->id,
+		       get_name(aux->btf, aux->func_info[0].type_id, aux->name),
+		       aux->attach_func_name, aux->linked_prog->aux->name);
+	return 0;
+}
+char LICENSE[] SEC("license") = "GPL";