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@xxxxxxxxx> 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@xxxxxxxxx>
> > ---
> > .../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?
