Merge branch 'bpftool-btf-support-dumping-a-single-type-from-file'

Daniel Xu says:

====================
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

=== Changelog ===

Changes in v5:
* Update bash-completion to support repeating root_id
* Update man page to mention root_id NAND map key/value/kv/all

Changes in v4:
* Support multiple instances of root_id

Changes in v3:
* Make `root_id` a top level btf-dump argument rather than attached to `file`
* Update bash completion script
* Refactor root_type_ids checking to after btf handle creation
* Update help messages and fix existing man page inconsistency

Changes in v2:
* Add early error check for invalid BTF ID
====================

Link: https://patch.msgid.link/cover.1734119028.git.dxu@dxuuu.xyz
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

1 files changed, 49 insertions, 2 deletions

diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index d005e4fd6128..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",
@@ -880,12 +882,14 @@ 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;
 	int fd = -1;
 	int err = 0;
+	int i;
 
 	if (!REQ_ARGS(2)) {
 		usage();
@@ -973,6 +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();
@@ -992,6 +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();
@@ -1017,6 +1053,17 @@ static int do_dump(int argc, char **argv)
 		}
 	}
 
+	/* Invalid root IDs causes half emitted boilerplate and then unclean
+	 * exit. It's an ugly user experience, so handle common error here.
+	 */
+	for (i = 0; i < root_type_cnt; i++) {
+		if (root_type_ids[i] >= btf__type_cnt(btf)) {
+			err = -EINVAL;
+			p_err("invalid root ID: %u", root_type_ids[i]);
+			goto done;
+		}
+	}
+
 	if (dump_c) {
 		if (json_output) {
 			p_err("JSON output for C-syntax dump is not supported");
@@ -1391,7 +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"