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bpf: Document bpf_inspect drgn tool

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It's a follow-up for discussion in [1].

drgn tool bpf_inspect.py was merged to drgn repo in [2]. Document it
in kernel tree to make BPF developers aware that the tool exists and
can help with getting BPF state unavailable via UAPI.

For now it's just one tool but the doc is written in a way that allows
to cover more tools in the future if needed.

Please refer to the doc itself for more details.

The patch was tested by `make htmldocs` and sanity-checking that
resulting html looks good.

v2 -> v3:
  - two sections: "Description" and "Getting started" (Daniel);
  - add examples in "Getting started" section (Daniel);
  - add "Customization" section to show how tool can be customized.

v1 -> v2:
  - better "BPF drgn tools" section (Alexei)

  [1] https://lore.kernel.org/bpf/20200228201514.GB51456@rdna-mbp/T/#mefed65e8a98116bd5d07d09a570a3eac46724951
  [2] https://github.com/osandov/drgn/pull/49

Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200324185135.1431038-1-rdna@fb.com
This commit is contained in:
Andrey Ignatov 2020-03-24 11:51:35 -07:00 committed by Daniel Borkmann
parent aa5e2af660
commit 8c061865f5
2 changed files with 216 additions and 2 deletions
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213
Documentation/bpf/drgn.rst Normal file
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@ -0,0 +1,213 @@
.. SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
==============
BPF drgn tools
==============
drgn scripts is a convenient and easy to use mechanism to retrieve arbitrary
kernel data structures. drgn is not relying on kernel UAPI to read the data.
Instead it's reading directly from ``/proc/kcore`` or vmcore and pretty prints
the data based on DWARF debug information from vmlinux.
This document describes BPF related drgn tools.
See `drgn/tools`_ for all tools available at the moment and `drgn/doc`_ for
more details on drgn itself.
bpf_inspect.py
--------------
Description
===========
`bpf_inspect.py`_ is a tool intended to inspect BPF programs and maps. It can
iterate over all programs and maps in the system and print basic information
about these objects, including id, type and name.
The main use-case `bpf_inspect.py`_ covers is to show BPF programs of types
``BPF_PROG_TYPE_EXT`` and ``BPF_PROG_TYPE_TRACING`` attached to other BPF
programs via ``freplace``/``fentry``/``fexit`` mechanisms, since there is no
user-space API to get this information.
Getting started
===============
List BPF programs (full names are obtained from BTF)::
% sudo bpf_inspect.py prog
27: BPF_PROG_TYPE_TRACEPOINT tracepoint__tcp__tcp_send_reset
4632: BPF_PROG_TYPE_CGROUP_SOCK_ADDR tw_ipt_bind
49464: BPF_PROG_TYPE_RAW_TRACEPOINT raw_tracepoint__sched_process_exit
List BPF maps::
% sudo bpf_inspect.py map
2577: BPF_MAP_TYPE_HASH tw_ipt_vips
4050: BPF_MAP_TYPE_STACK_TRACE stack_traces
4069: BPF_MAP_TYPE_PERCPU_ARRAY ned_dctcp_cntr
Find BPF programs attached to BPF program ``test_pkt_access``::
% sudo bpf_inspect.py p | grep test_pkt_access
650: BPF_PROG_TYPE_SCHED_CLS test_pkt_access
654: BPF_PROG_TYPE_TRACING test_main linked:[650->25: BPF_TRAMP_FEXIT test_pkt_access->test_pkt_access()]
655: BPF_PROG_TYPE_TRACING test_subprog1 linked:[650->29: BPF_TRAMP_FEXIT test_pkt_access->test_pkt_access_subprog1()]
656: BPF_PROG_TYPE_TRACING test_subprog2 linked:[650->31: BPF_TRAMP_FEXIT test_pkt_access->test_pkt_access_subprog2()]
657: BPF_PROG_TYPE_TRACING test_subprog3 linked:[650->21: BPF_TRAMP_FEXIT test_pkt_access->test_pkt_access_subprog3()]
658: BPF_PROG_TYPE_EXT new_get_skb_len linked:[650->16: BPF_TRAMP_REPLACE test_pkt_access->get_skb_len()]
659: BPF_PROG_TYPE_EXT new_get_skb_ifindex linked:[650->23: BPF_TRAMP_REPLACE test_pkt_access->get_skb_ifindex()]
660: BPF_PROG_TYPE_EXT new_get_constant linked:[650->19: BPF_TRAMP_REPLACE test_pkt_access->get_constant()]
It can be seen that there is a program ``test_pkt_access``, id 650 and there
are multiple other tracing and ext programs attached to functions in
``test_pkt_access``.
For example the line::
658: BPF_PROG_TYPE_EXT new_get_skb_len linked:[650->16: BPF_TRAMP_REPLACE test_pkt_access->get_skb_len()]
, means that BPF program id 658, type ``BPF_PROG_TYPE_EXT``, name
``new_get_skb_len`` replaces (``BPF_TRAMP_REPLACE``) function ``get_skb_len()``
that has BTF id 16 in BPF program id 650, name ``test_pkt_access``.
Getting help:
.. code-block:: none
% sudo bpf_inspect.py
usage: bpf_inspect.py [-h] {prog,p,map,m} ...
drgn script to list BPF programs or maps and their properties
unavailable via kernel API.
See https://github.com/osandov/drgn/ for more details on drgn.
optional arguments:
-h, --help show this help message and exit
subcommands:
{prog,p,map,m}
prog (p) list BPF programs
map (m) list BPF maps
Customization
=============
The script is intended to be customized by developers to print relevant
information about BPF programs, maps and other objects.
For example, to print ``struct bpf_prog_aux`` for BPF program id 53077:
.. code-block:: none
% git diff
diff --git a/tools/bpf_inspect.py b/tools/bpf_inspect.py
index 650e228..aea2357 100755
--- a/tools/bpf_inspect.py
+++ b/tools/bpf_inspect.py
@@ -112,7 +112,9 @@ def list_bpf_progs(args):
if linked:
linked = f" linked:[{linked}]"
- print(f"{id_:>6}: {type_:32} {name:32} {linked}")
+ if id_ == 53077:
+ print(f"{id_:>6}: {type_:32} {name:32}")
+ print(f"{bpf_prog.aux}")
def list_bpf_maps(args):
It produces the output::
% sudo bpf_inspect.py p
53077: BPF_PROG_TYPE_XDP tw_xdp_policer
*(struct bpf_prog_aux *)0xffff8893fad4b400 = {
.refcnt = (atomic64_t){
.counter = (long)58,
},
.used_map_cnt = (u32)1,
.max_ctx_offset = (u32)8,
.max_pkt_offset = (u32)15,
.max_tp_access = (u32)0,
.stack_depth = (u32)8,
.id = (u32)53077,
.func_cnt = (u32)0,
.func_idx = (u32)0,
.attach_btf_id = (u32)0,
.linked_prog = (struct bpf_prog *)0x0,
.verifier_zext = (bool)0,
.offload_requested = (bool)0,
.attach_btf_trace = (bool)0,
.func_proto_unreliable = (bool)0,
.trampoline_prog_type = (enum bpf_tramp_prog_type)BPF_TRAMP_FENTRY,
.trampoline = (struct bpf_trampoline *)0x0,
.tramp_hlist = (struct hlist_node){
.next = (struct hlist_node *)0x0,
.pprev = (struct hlist_node **)0x0,
},
.attach_func_proto = (const struct btf_type *)0x0,
.attach_func_name = (const char *)0x0,
.func = (struct bpf_prog **)0x0,
.jit_data = (void *)0x0,
.poke_tab = (struct bpf_jit_poke_descriptor *)0x0,
.size_poke_tab = (u32)0,
.ksym_tnode = (struct latch_tree_node){
.node = (struct rb_node [2]){
{
.__rb_parent_color = (unsigned long)18446612956263126665,
.rb_right = (struct rb_node *)0x0,
.rb_left = (struct rb_node *)0xffff88a0be3d0088,
},
{
.__rb_parent_color = (unsigned long)18446612956263126689,
.rb_right = (struct rb_node *)0x0,
.rb_left = (struct rb_node *)0xffff88a0be3d00a0,
},
},
},
.ksym_lnode = (struct list_head){
.next = (struct list_head *)0xffff88bf481830b8,
.prev = (struct list_head *)0xffff888309f536b8,
},
.ops = (const struct bpf_prog_ops *)xdp_prog_ops+0x0 = 0xffffffff820fa350,
.used_maps = (struct bpf_map **)0xffff889ff795de98,
.prog = (struct bpf_prog *)0xffffc9000cf2d000,
.user = (struct user_struct *)root_user+0x0 = 0xffffffff82444820,
.load_time = (u64)2408348759285319,
.cgroup_storage = (struct bpf_map *[2]){},
.name = (char [16])"tw_xdp_policer",
.security = (void *)0xffff889ff795d548,
.offload = (struct bpf_prog_offload *)0x0,
.btf = (struct btf *)0xffff8890ce6d0580,
.func_info = (struct bpf_func_info *)0xffff889ff795d240,
.func_info_aux = (struct bpf_func_info_aux *)0xffff889ff795de20,
.linfo = (struct bpf_line_info *)0xffff888a707afc00,
.jited_linfo = (void **)0xffff8893fad48600,
.func_info_cnt = (u32)1,
.nr_linfo = (u32)37,
.linfo_idx = (u32)0,
.num_exentries = (u32)0,
.extable = (struct exception_table_entry *)0xffffffffa032d950,
.stats = (struct bpf_prog_stats *)0x603fe3a1f6d0,
.work = (struct work_struct){
.data = (atomic_long_t){
.counter = (long)0,
},
.entry = (struct list_head){
.next = (struct list_head *)0x0,
.prev = (struct list_head *)0x0,
},
.func = (work_func_t)0x0,
},
.rcu = (struct callback_head){
.next = (struct callback_head *)0x0,
.func = (void (*)(struct callback_head *))0x0,
},
}
.. Links
.. _drgn/doc: https://drgn.readthedocs.io/en/latest/
.. _drgn/tools: https://github.com/osandov/drgn/tree/master/tools
.. _bpf_inspect.py:
https://github.com/osandov/drgn/blob/master/tools/bpf_inspect.py

5
Documentation/bpf/index.rst
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@ -47,12 +47,13 @@ Program types
prog_flow_dissector
Testing BPF
===========
Testing and debugging BPF
=========================
.. toctree::
:maxdepth: 1
drgn
s390