Commit a812d92e authored by Daniel Xu's avatar Daniel Xu Committed by Andrii Nakryiko
Browse files

bpftool: btf: Support dumping a specific types from file 

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: default avatarDaniel Xu <dxu@dxuuu.xyz>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/04feb860c0a56a7da66f923551484e1483a72074.1734119028.git.dxu@dxuuu.xyz
parent 7f5819e1

tools/bpf/bpftool/Documentation/bpftool-btf.rst

+7 −2
Original line number Diff line number Diff line
@@ -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 +67,11 @@ 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

    (such as the "key", "value", or "kv" arguments when dumping BTF for a map).

    It can be passed multiple times to dump multiple types.



bpftool btf help

    Print short help message.

tools/bpf/bpftool/btf.c

+37 −2
Original line number Diff line number Diff line
@@ -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);

				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"