linux-kernel - [PATCH v2 bpf-next 0/3] bpf: support module BTF in BTF display helpers

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Message-Id: <1607107716-14135-1-git-send-email-alan.maguire@oracle.com>
Date:   Fri,  4 Dec 2020 18:48:33 +0000
From:   Alan Maguire <alan.maguire@...cle.com>
To:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org
Cc:     kafai@...com, yhs@...com, songliubraving@...com,
        john.fastabend@...il.com, kpsingh@...omium.org,
        rostedt@...dmis.org, mingo@...hat.com, haoluo@...gle.com,
        jolsa@...nel.org, quentin@...valent.com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, shuah@...nel.org, lmb@...udflare.com,
        linux-kselftest@...r.kernel.org,
        Alan Maguire <alan.maguire@...cle.com>
Subject: [PATCH v2 bpf-next 0/3] bpf: support module BTF in BTF display helpers

This series aims to add support to bpf_snprintf_btf() and
bpf_seq_printf_btf() allowing them to store string representations
of module-specific types, as well as the kernel-specific ones
they currently support.

Patch 1 removes the btf_module_mutex, as since we will need to
look up module BTF during BPF program execution, we don't want
to risk sleeping in the various contexts in which BPF can run.
The access patterns to the btf module list seem to conform to
classic list RCU usage so with a few minor tweaks this seems
workable.

Patch 2 replaces the unused flags field in struct btf_ptr with
an obj_id field,  allowing the specification of the id of a
BTF module.  If the value is 0, the core kernel vmlinux is
assumed to contain the type's BTF information.  Otherwise the
module with that id is used to identify the type.  If the
object-id based lookup fails, we again fall back to vmlinux
BTF.

Patch 3 is a selftest that uses veth (when built as a
module) and a kprobe to display both a module-specific
and kernel-specific type; both are arguments to veth_stats_rx().
Currently it looks up the module-specific type and object ids
using libbpf; in future, these lookups will likely be supported
directly in the BPF program via __builtin_btf_type_id(); but
I need to determine a good test to determine if that builtin
supports object ids.

Changes since RFC

- add patch to remove module mutex
- modify to use obj_id instead of module name as identifier
  in "struct btf_ptr" (Andrii)

Alan Maguire (3):
  bpf: eliminate btf_module_mutex as RCU synchronization can be used
  bpf: add module support to btf display helpers
  selftests/bpf: verify module-specific types can be shown via
    bpf_snprintf_btf

 include/linux/btf.h                                |  12 ++
 include/uapi/linux/bpf.h                           |  13 ++-
 kernel/bpf/btf.c                                   |  49 +++++---
 kernel/trace/bpf_trace.c                           |  44 ++++++--
 tools/include/uapi/linux/bpf.h                     |  13 ++-
 .../selftests/bpf/prog_tests/snprintf_btf_mod.c    | 124 +++++++++++++++++++++
 tools/testing/selftests/bpf/progs/bpf_iter.h       |   2 +-
 tools/testing/selftests/bpf/progs/btf_ptr.h        |   2 +-
 tools/testing/selftests/bpf/progs/veth_stats_rx.c  |  72 ++++++++++++
 9 files changed, 292 insertions(+), 39 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/snprintf_btf_mod.c
 create mode 100644 tools/testing/selftests/bpf/progs/veth_stats_rx.c

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