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Message-ID: <CAEf4BzaA9_up=3npADgJv8pCVg4eVzsWevef69c3PkdyuWNXDQ@mail.gmail.com>
Date: Thu, 12 Dec 2024 11:09:34 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Daniel Xu <dxu@...uu.xyz>
Cc: hawk@...nel.org, john.fastabend@...il.com, ast@...nel.org, qmo@...nel.org,
davem@...emloft.net, daniel@...earbox.net, andrii@...nel.org, kuba@...nel.org,
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, antony@...nome.org,
toke@...nel.org
Subject: Re: [PATCH bpf-next v3 3/4] bpftool: btf: Support dumping a single
type from file
On Mon, Dec 9, 2024 at 3:45 PM Daniel Xu <dxu@...uu.xyz> wrote:
>
> 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 single type by
> providing an optional root_id argument.
>
> 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 | 7 +++++--
> tools/bpf/bpftool/btf.c | 21 ++++++++++++++++++-
> 2 files changed, 25 insertions(+), 3 deletions(-)
>
> diff --git a/tools/bpf/bpftool/Documentation/bpftool-btf.rst b/tools/bpf/bpftool/Documentation/bpftool-btf.rst
> index 245569f43035..4899b2c10777 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 +67,9 @@ 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.
> +
> bpftool btf help
> Print short help message.
>
> diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> index 3e995faf9efa..18b037a1414b 100644
> --- a/tools/bpf/bpftool/btf.c
> +++ b/tools/bpf/bpftool/btf.c
> @@ -993,6 +993,25 @@ 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 (root_type_cnt) {
> + p_err("cannot use root_id with other type filtering");
this is a confusing error if the user just wanted to provide two
root_id arguments... Also, why don't we allow multiple root_ids?
I'd bump root_type_ids[] to have something like 16 elements or
something (though we can always do dynamic realloc as well, probably),
and allow multiple types to be specified.
Thoughts?
> + err = -EINVAL;
> + 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;
> + }
> + root_type_ids[root_type_cnt++] = root_id;
> + NEXT_ARG();
> } else if (is_prefix(*argv, "unsorted")) {
> sort_dump_c = false;
> NEXT_ARG();
> @@ -1403,7 +1422,7 @@ 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"
> --
> 2.46.0
>
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