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Date: Wed, 24 Apr 2019 11:12:46 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Yonghong Song <yhs@...com>
Cc: Kernel Team <Kernel-team@...com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>,
Alexei Starovoitov <ast@...com>,
"daniel@...earbox.net" <daniel@...earbox.net>,
Song Liu <songliubraving@...com>, Martin Lau <kafai@...com>,
"acme@...nel.org" <acme@...nel.org>,
Andrii Nakryiko <andriin@...com>,
Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH bpf-next 1/2] bpftool: add ability to dump BTF types
On Wed, Apr 24, 2019 at 10:12 AM Yonghong Song <yhs@...com> wrote:
>
>
>
> On 4/23/19 10:21 PM, andrii.nakryiko@...il.com wrote:
> > From: Andrii Nakryiko <andriin@...com>
> >
> > Add new `btf dump` sub-command to bpftool. It allows to dump
> > human-readable low-level BTF types representation of BTF types. BTF can
> > be retrieved from few different sources:
> > - from BTF object by ID;
> > - from PROG, if it has associated BTF;
> > - from MAP, if it has associated BTF data; it's possible to narrow
> > down types to either key type, value type, both, or all BTF types;
> > - from ELF file (.BTF section).
> This is great. Thanks!
> >
> > Output format mostly follows BPF verifier log format with few notable
> > exceptions:
> > - all the type/field/param/etc names are enclosed in single quotes to
> > allow easier grepping and to stand out a little bit more;
> > - FUNC_PROTO output follows STRUCT/UNION/ENUM format of having one
> > line per each argument; this is more uniform and allows easy
> > grepping, as opposed to succinct, but inconvenient format that BPF
> > verifier log is using.
> >
> > Cc: Daniel Borkmann <daniel@...earbox.net>
> > Cc: Alexei Starovoitov <ast@...com>
> > Cc: Yonghong Song <yhs@...com>
> > Cc: Martin KaFai Lau <kafai@...com>
> > Cc: Song Liu <songliubraving@...com>
> > Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> > Signed-off-by: Andrii Nakryiko <andriin@...com>
> > ---
> > tools/bpf/bpftool/btf.c | 576 +++++++++++++++++++++++++++++++++++++++
> > tools/bpf/bpftool/main.c | 1 +
> > tools/bpf/bpftool/main.h | 1 +
> > 3 files changed, 578 insertions(+)
> > create mode 100644 tools/bpf/bpftool/btf.c
> >
> > diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> > new file mode 100644
> > index 000000000000..afe5cb7bab0c
> > --- /dev/null
> > +++ b/tools/bpf/bpftool/btf.c
> > @@ -0,0 +1,576 @@
> > +// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +/* Copyright (C) 2019 Facebook */
> > +
> > +#include <errno.h>
> > +#include <fcntl.h>
> > +#include <linux/err.h>
> > +#include <stdbool.h>
> > +#include <stdio.h>
> > +#include <string.h>
> > +#include <unistd.h>
> > +#include <gelf.h>
> > +#include <bpf.h>
> > +#include <linux/btf.h>
> > +
> [.....]
> > +
> > +static int do_dump(int argc, char **argv)
> > +{
> > + struct btf *btf = NULL;
> > + __u32 root_type_ids[2];
> > + int root_type_cnt = 0;
> > + __u32 btf_id = -1;
> > + const char *src;
> > + int fd = -1;
> > + int err;
> > +
> > + if (!REQ_ARGS(2)) {
> > + usage();
> > + return -1;
> > + }
> > + src = GET_ARG();
> > +
> > + if (is_prefix(src, "map")) {
> > + struct bpf_map_info info = {};
> > + __u32 len = sizeof(info);
> > +
> > + if (!REQ_ARGS(2)) {
> > + usage();
> > + return -1;
> > + }
> > +
> > + fd = map_parse_fd_and_info(&argc, &argv, &info, &len);
> > + if (fd < 0)
> > + return -1;
> > +
> > + btf_id = info.btf_id;
> > + if (argc && is_prefix(*argv, "key")) {
> > + root_type_ids[root_type_cnt++] = info.btf_key_type_id;
> > + NEXT_ARG();
> > + } else if (argc && is_prefix(*argv, "value")) {
> > + root_type_ids[root_type_cnt++] = info.btf_value_type_id;
> > + NEXT_ARG();
> > + } else if (argc && is_prefix(*argv, "all")) {
> > + NEXT_ARG();
> > + } else if (argc && is_prefix(*argv, "kv")) {
> > + root_type_ids[root_type_cnt++] = info.btf_key_type_id;
> > + root_type_ids[root_type_cnt++] = info.btf_value_type_id;
> > + NEXT_ARG();
> > + } else {
> > + root_type_ids[root_type_cnt++] = info.btf_key_type_id;
> > + root_type_ids[root_type_cnt++] = info.btf_value_type_id;
> > + }
> > + } else if (is_prefix(src, "prog")) {
> > + struct bpf_prog_info info = {};
> > + __u32 len = sizeof(info);
> > +
> > + if (!REQ_ARGS(2)) {
> > + usage();
> > + return -1;
> > + }
> > +
> > + fd = prog_parse_fd(&argc, &argv);
> > + if (fd < 0)
> > + return -1;
> > +
> > + err = bpf_obj_get_info_by_fd(fd, &info, &len);
> > + if (err) {
> > + p_err("can't get prog info: %s", strerror(errno));
> > + goto done;
> > + }
> > +
> > + btf_id = info.btf_id;
> > + } else if (is_prefix(src, "id")) {
> > + char *endptr;
> > +
> > + btf_id = strtoul(*argv, &endptr, 0);
> > + if (*endptr) {
> > + p_err("can't parse %s as ID", **argv);
> > + return -1;
> > + }
> > + NEXT_ARG();
> > + } else if (is_prefix(src, "file")) {
> > + err = btf_load_from_elf(*argv, &btf);
> > + if (err)
> > + goto done;
> > + NEXT_ARG();
> > + }
>
> Another "else" branch here to handle wrong prefix? Otherwise, it will
> fall down to "can't find btf with ID (4294967295)" where "4294967295 ==
> -1) which is a little misleading for users.
Yep, makes sense, will add, not sure why I haven't done that in the
first place...
>
> > +
> > + if (!btf) {
> > + err = btf__get_from_id(btf_id, &btf);
> > + if (err) {
> > + p_err("get btf by id (%u): %s", btf_id, strerror(err));
> > + goto done;
> > + }
> > + if (!btf) {
> > + err = ENOENT;
> > + p_err("can't find btf with ID (%u)", btf_id);
> > + goto done;
> > + }
> > + }
> > +
> > + dump_btf_raw(btf, root_type_ids, root_type_cnt);
> > +
> > +done:
> > + close(fd);
> > + btf__free(btf);
> > + return err;
> > +}
> > +
> > +static int do_help(int argc, char **argv)
> > +{
> > + if (json_output) {
> > + jsonw_null(json_wtr);
> > + return 0;
> > + }
> > +
> > + fprintf(stderr,
> > + "Usage: %s btf dump BTF_SRC\n"
> > + " %s btf help\n"
> > + "\n"
> > + " BTF_SRC := { id BTF_ID | prog PROG | map MAP [{key | value | kv | all}] | elf FILE }\n"
>
> "elf FILE" is not consistent with implementation. The implementation
> uses "file FILE". I prefer to use "file FILE".
Oops, yep, it should be file.
>
> > + " " HELP_SPEC_MAP "\n"
> > + " " HELP_SPEC_PROGRAM "\n"
> > + " " HELP_SPEC_OPTIONS "\n"
> > + "",
> > + bin_name, bin_name);
> > +
> > + return 0;
> > +}
> > +
> > +static const struct cmd cmds[] = {
> > + { "help", do_help },
> > + { "dump", do_dump },
> > + { 0 }
> > +};
> > +
> > +int do_btf(int argc, char **argv)
> > +{
> > + return cmd_select(cmds, argc, argv, do_help);
> > +}
> > diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
> > index a9d5e9e6a732..eba56edd7c77 100644
> > --- a/tools/bpf/bpftool/main.c
> > +++ b/tools/bpf/bpftool/main.c
> > @@ -188,6 +188,7 @@ static const struct cmd cmds[] = {
> > { "perf", do_perf },
> > { "net", do_net },
> > { "feature", do_feature },
> > + { "btf", do_btf },
> > { "version", do_version },
> > { 0 }
> > };
> > diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
> > index 1ccc46169a19..3d63feb7f852 100644
> > --- a/tools/bpf/bpftool/main.h
> > +++ b/tools/bpf/bpftool/main.h
> > @@ -150,6 +150,7 @@ int do_perf(int argc, char **arg);
> > int do_net(int argc, char **arg);
> > int do_tracelog(int argc, char **arg);
> > int do_feature(int argc, char **argv);
> > +int do_btf(int argc, char **argv);
> >
> > int parse_u32_arg(int *argc, char ***argv, __u32 *val, const char *what);
> > int prog_parse_fd(int *argc, char ***argv);
> >
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