On Fri, Dec 13, 2024 at 04:55:34PM GMT, Quentin Monnet wrote:
> 2024-12-13 09:45 UTC-0700 ~ Daniel Xu <dxu@xxxxxxxxx>
> > Hi Quentin,
> >
> > On Fri, Dec 13, 2024 at 03:17:36PM GMT, Quentin Monnet wrote:
> >> 2024-12-12 18:24 UTC-0700 ~ Daniel Xu <dxu@xxxxxxxxx>
> >>> 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@xxxxxxxxx>
> >>> ---
> >>> .../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?
> >
> > The above `if (have_id_filtering)` check prevents mixing key/value/kv
> > map args with root_id. That ought to prevent overcounting, right?
>
> Ah, you're right, you even mentioned it in the docs, sorry. All good on
> that side, then.
>
> Regarding the restriction, would you mind making the mention from the
> man page a bit more explicit, please? Something along:
>
> [...] It cannot be used with any other types of filtering, such as
> the "key", "value", or "kv" arguments when dumping BTF for a map.
> **root_id** can be passed multiple times...
Ack, will do.
