linux-kernel - [PATCH bpf-next v3 3/4] bpftool: btf: Support dumping a single type from file

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Message-ID: <3bc17d33161961409dc77a5de29761bf2bed4980.1733787798.git.dxu@dxuuu.xyz>
Date: Mon,  9 Dec 2024 16:44:34 -0700
From: Daniel Xu <dxu@...uu.xyz>
To: hawk@...nel.org,
	john.fastabend@...il.com,
	ast@...nel.org,
	qmo@...nel.org,
	davem@...emloft.net,
	daniel@...earbox.net,
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Cc: martin.lau@...ux.dev,
	eddyz87@...il.com,
	song@...nel.org,
	yonghong.song@...ux.dev,
	kpsingh@...nel.org,
	sdf@...ichev.me,
	haoluo@...gle.com,
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	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
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Subject: [PATCH bpf-next v3 3/4] bpftool: btf: Support dumping a single type 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 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");
+				err = -EINVAL;
+				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;
+			}
+			root_type_ids[root_type_cnt++] = root_id;
+			NEXT_ARG();
 		} else if (is_prefix(*argv, "unsorted")) {
 			sort_dump_c = false;
 			NEXT_ARG();
@@ -1403,7 +1422,7 @@ 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"
-- 
2.46.0