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Message-ID: <CAEf4BzZOL5f4m=y6P0RF5=QtcegEDNXKXPav4uqVy97VN0kLOQ@mail.gmail.com>
Date: Thu, 12 Dec 2024 16:12:00 -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 Thu, Dec 12, 2024 at 3:41 PM Daniel Xu <dxu@...uu.xyz> wrote:
>
> On Thu, Dec 12, 2024 at 11:09:34AM GMT, Andrii Nakryiko wrote:
> > 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?
>
> That's a good point. I added this check b/c I didn't think it would
> make sense to allow `root_id` filtering in combination with map dump
> filtering (which uses same root_type_ids param):
>
> map MAP [{key | value | kv | all}]
>
> But code can easily be tweaked to still block combination but allow
> multiple `root_id`s when used alone. 16 seems sufficient to me.
>
> Do you think it'd be more bpftool-y to require "root_id" each time or to
> just take a comma separated value?
root_id 123 root_id 345 root_id 789
definitely more bpftool-y
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