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/[e-mail]
Signed-off-by: Andrii Nakryiko <[e-mail]>

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

···
 =============
 
 | **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* }
···
     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*
+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
···
     (**raw**) or C-syntax (**c**) output formats are supported. With C-style
     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/bash-completion/bpftool

···
                         format)
                             COMPREPLY=( $( compgen -W "c raw" -- "$cur" ) )
                             ;;
+                        root_id)
+                            return 0;
+                            ;;
                         c)
-                            COMPREPLY=( $( compgen -W "unsorted" -- "$cur" ) )
+                            COMPREPLY=( $( compgen -W "unsorted root_id" -- "$cur" ) )
                             ;;
                         *)
                             # emit extra options
                             case ${words[3]} in
                                 id|file)
+                                    COMPREPLY=( $( compgen -W "root_id" -- "$cur" ) )
                                     _bpftool_once_attr 'format'
                                     ;;
                                 map|prog)
                                     if [[ ${words[3]} == "map" ]] && [[ $cword == 6 ]]; then
                                         COMPREPLY+=( $( compgen -W "key value kv all" -- "$cur" ) )
                                     fi
+                                    COMPREPLY=( $( compgen -W "root_id" -- "$cur" ) )
                                     _bpftool_once_attr 'format'
                                     ;;
                                 *)

tools/bpf/bpftool/btf.c

···
 #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",
···
 {
 	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();
···
 		goto done;
 	}
 
+	have_id_filtering = !!root_type_cnt;
+
 	while (argc) {
 		if (is_prefix(*argv, "format")) {
 			NEXT_ARG();
···
 				err = -EINVAL;
 				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;
···
 		if (!btf) {
 			err = -errno;
 			p_err("get btf by id (%u): %s", btf_id, strerror(errno));
+			goto done;
+		}
+	}
+
+	/* 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;
 		}
 	}
···
 
 	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"