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bpftool: btf: Support dumping a specific types from file

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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@dxuuu.xyz>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/04feb860c0a56a7da66f923551484e1483a72074.1734119028.git.dxu@dxuuu.xyz
This commit is contained in:
Daniel Xu 2024-12-13 12:44:11 -07:00 committed by Andrii Nakryiko
parent 7f5819e1ac
commit a812d92ed2
2 changed files with 44 additions and 4 deletions
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9
tools/bpf/bpftool/Documentation/bpftool-btf.rst
View File

@ -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.

39
tools/bpf/bpftool/btf.c
View File

@ -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"