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Message-ID: <7fa902e5-0916-4bc9-b1e0-2729903d3de0@kernel.org>
Date: Fri, 13 Dec 2024 15:17:36 +0000
From: Quentin Monnet <qmo@...nel.org>
To: Daniel Xu <dxu@...uu.xyz>, hawk@...nel.org, kuba@...nel.org,
andrii@...nel.org, john.fastabend@...il.com, ast@...nel.org,
daniel@...earbox.net, davem@...emloft.net
Cc: martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org,
yonghong.song@...ux.dev, kpsingh@...nel.org, sdf@...ichev.me,
haoluo@...gle.com, jolsa@...nel.org, bpf@...r.kernel.org,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
andrii.nakryiko@...il.com, antony@...nome.org, toke@...nel.org
Subject: Re: [PATCH bpf-next v4 3/4] bpftool: btf: Support dumping a specific
types from file
2024-12-12 18:24 UTC-0700 ~ Daniel Xu <dxu@...uu.xyz>
> Some projects, for example xdp-tools [0], prefer to check in a minimized
> vmlinux.h rather than the complete file which can get rather large.
>
> However, when you try to add a minimized version of a complex struct (eg
> struct xfrm_state), things can get quite complex if you're trying to
> manually untangle and deduplicate the dependencies.
>
> This commit teaches bpftool to do a minimized dump of a specific types by
> providing a optional root_id argument(s).
>
> Example usage:
>
> $ ./bpftool btf dump file ~/dev/linux/vmlinux | rg "STRUCT 'xfrm_state'"
> [12643] STRUCT 'xfrm_state' size=912 vlen=58
>
> $ ./bpftool btf dump file ~/dev/linux/vmlinux root_id 12643 format c
> #ifndef __VMLINUX_H__
> #define __VMLINUX_H__
>
> [..]
>
> struct xfrm_type_offload;
>
> struct xfrm_sec_ctx;
>
> struct xfrm_state {
> possible_net_t xs_net;
> union {
> struct hlist_node gclist;
> struct hlist_node bydst;
> };
> union {
> struct hlist_node dev_gclist;
> struct hlist_node bysrc;
> };
> struct hlist_node byspi;
> [..]
>
> [0]: https://github.com/xdp-project/xdp-tools/blob/master/headers/bpf/vmlinux.h
>
> Signed-off-by: Daniel Xu <dxu@...uu.xyz>
> ---
> .../bpf/bpftool/Documentation/bpftool-btf.rst | 8 +++-
> tools/bpf/bpftool/btf.c | 39 ++++++++++++++++++-
> 2 files changed, 43 insertions(+), 4 deletions(-)
>
> diff --git a/tools/bpf/bpftool/Documentation/bpftool-btf.rst b/tools/bpf/bpftool/Documentation/bpftool-btf.rst
> index 245569f43035..dbe6d6d94e4c 100644
> --- a/tools/bpf/bpftool/Documentation/bpftool-btf.rst
> +++ b/tools/bpf/bpftool/Documentation/bpftool-btf.rst
> @@ -24,7 +24,7 @@ BTF COMMANDS
> =============
>
> | **bpftool** **btf** { **show** | **list** } [**id** *BTF_ID*]
> -| **bpftool** **btf dump** *BTF_SRC* [**format** *FORMAT*]
> +| **bpftool** **btf dump** *BTF_SRC* [**format** *FORMAT*] [**root_id** *ROOT_ID*]
> | **bpftool** **btf help**
> |
> | *BTF_SRC* := { **id** *BTF_ID* | **prog** *PROG* | **map** *MAP* [{**key** | **value** | **kv** | **all**}] | **file** *FILE* }
> @@ -43,7 +43,7 @@ bpftool btf { show | list } [id *BTF_ID*]
> that hold open file descriptors (FDs) against BTF objects. On such kernels
> bpftool will automatically emit this information as well.
>
> -bpftool btf dump *BTF_SRC* [format *FORMAT*]
> +bpftool btf dump *BTF_SRC* [format *FORMAT*] [root_id *ROOT_ID*]
> Dump BTF entries from a given *BTF_SRC*.
>
> When **id** is specified, BTF object with that ID will be loaded and all
> @@ -67,6 +67,10 @@ bpftool btf dump *BTF_SRC* [format *FORMAT*]
> formatting, the output is sorted by default. Use the **unsorted** option
> to avoid sorting the output.
>
> + **root_id** option can be used to filter a dump to a single type and all
> + its dependent types. It cannot be used with any other types of filtering.
> + It can be passed multiple times to dump multiple types.
> +
> bpftool btf help
> Print short help message.
>
> diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> index 3e995faf9efa..2636655ac180 100644
> --- a/tools/bpf/bpftool/btf.c
> +++ b/tools/bpf/bpftool/btf.c
> @@ -27,6 +27,8 @@
> #define KFUNC_DECL_TAG "bpf_kfunc"
> #define FASTCALL_DECL_TAG "bpf_fastcall"
>
> +#define MAX_ROOT_IDS 16
> +
> static const char * const btf_kind_str[NR_BTF_KINDS] = {
> [BTF_KIND_UNKN] = "UNKNOWN",
> [BTF_KIND_INT] = "INT",
> @@ -880,7 +882,8 @@ static int do_dump(int argc, char **argv)
> {
> bool dump_c = false, sort_dump_c = true;
> struct btf *btf = NULL, *base = NULL;
> - __u32 root_type_ids[2];
> + __u32 root_type_ids[MAX_ROOT_IDS];
> + bool have_id_filtering;
> int root_type_cnt = 0;
> __u32 btf_id = -1;
> const char *src;
> @@ -974,6 +977,8 @@ static int do_dump(int argc, char **argv)
> goto done;
> }
>
> + have_id_filtering = !!root_type_cnt;
> +
> while (argc) {
> if (is_prefix(*argv, "format")) {
> NEXT_ARG();
> @@ -993,6 +998,36 @@ static int do_dump(int argc, char **argv)
> goto done;
> }
> NEXT_ARG();
> + } else if (is_prefix(*argv, "root_id")) {
> + __u32 root_id;
> + char *end;
> +
> + if (have_id_filtering) {
> + p_err("cannot use root_id with other type filtering");
> + err = -EINVAL;
> + goto done;
> + } else if (root_type_cnt == MAX_ROOT_IDS) {
> + p_err("only %d root_id are supported", MAX_ROOT_IDS);
I doubt users will often reach this limit, but if they do, the message
can be confusing, because MAX_ROOT_IDS also accounts for root_type_ids[]
cells used when we pass map arguments ("key" or "value" or "kv"), so you
could pass 15 "root_id" on the command line and get a message telling
only 16 are supported.
Maybe add a counter to tell how many were defined from the rest of the
command line, and adjust the value in the error message?
> + err = -E2BIG;
> + goto done;
> + }
> +
> + NEXT_ARG();
> + root_id = strtoul(*argv, &end, 0);
> + if (*end) {
> + err = -1;
> + p_err("can't parse %s as root ID", *argv);
> + goto done;
> + }
> + for (i = 0; i < root_type_cnt; i++) {
> + if (root_type_ids[i] == root_id) {
> + err = -EINVAL;
> + p_err("duplicate root_id %d supplied", root_id);
> + goto done;
> + }
> + }
> + root_type_ids[root_type_cnt++] = root_id;
> + NEXT_ARG();
> } else if (is_prefix(*argv, "unsorted")) {
> sort_dump_c = false;
> NEXT_ARG();
> @@ -1403,7 +1438,7 @@ static int do_help(int argc, char **argv)
>
> fprintf(stderr,
> "Usage: %1$s %2$s { show | list } [id BTF_ID]\n"
> - " %1$s %2$s dump BTF_SRC [format FORMAT]\n"
> + " %1$s %2$s dump BTF_SRC [format FORMAT] [root_id ROOT_ID]\n"
> " %1$s %2$s help\n"
> "\n"
> " BTF_SRC := { id BTF_ID | prog PROG | map MAP [{key | value | kv | all}] | file FILE }\n"
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