Re: [PATCH v4 bpf-next 2/4] bpf: Add BPF program and map iterators as built-in BPF programs.

On Fri, Jul 24, 2020 at 1:39 PM Alexei Starovoitov
[off-list ref] wrote:

From: Alexei Starovoitov <ast@kernel.org>

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            pages
   3 iterator.rodata     2

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>
---

Tiny bug below, otherwise looks good.

Acked-by: Andrii Nakryiko <redacted>

 kernel/bpf/preload/iterators/.gitignore       |   2 +
 kernel/bpf/preload/iterators/Makefile         |  57 +++
 kernel/bpf/preload/iterators/README           |   4 +
 kernel/bpf/preload/iterators/iterators.bpf.c  | 118 +++++
 kernel/bpf/preload/iterators/iterators.skel.h | 411 ++++++++++++++++++
 5 files changed, 592 insertions(+)
 create mode 100644 kernel/bpf/preload/iterators/.gitignore
 create mode 100644 kernel/bpf/preload/iterators/Makefile
 create mode 100644 kernel/bpf/preload/iterators/README
 create mode 100644 kernel/bpf/preload/iterators/iterators.bpf.c
 create mode 100644 kernel/bpf/preload/iterators/iterators.skel.h

[...]

+
+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)

= here?

+               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             pages\n");
+
+       BPF_SEQ_PRINTF(seq, "%4u %-16s%6d\n", map->id, map->name, map->memory.pages);

map->memory.pages won't be meaningful, once Roman's patches removing
RLIMIT_MEMLOCK usage land, so might just drop them now

+       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";

[...]