btf_module_ids.c

// SPDX-License-Identifier: GPL-2.0+

#include <stdlib.h>
#include <errno.h>
#include <stdio.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <getopt.h>

#include <bpf/libbpf.h>
#include <bpf/bpf.h>
#include <bpf/btf.h> /* Notice libbpf BTF include */

#include <linux/err.h>

static const struct option long_options[] = {
	{ "debug",		no_argument,		NULL,	'd' },
	{ "module-name",	required_argument,	NULL,	'm' },
	{ 0, 0, NULL, 0 }
};

static char module_name[128] = "tun"; /* Default module to lookup */

int print_all_levels(enum libbpf_print_level level,
		     const char *format, va_list args)
{
	return vfprintf(stderr, format, args);
}

#define pr_err(fmt, ...) \
	fprintf(stderr, "%s:%d - " fmt, __FILE__, __LINE__, ##__VA_ARGS__)

static inline __u64 ptr_to_u64(const void *ptr)
{
	return (__u64) (unsigned long) ptr;
}

static inline void *u64_to_ptr(__u64 val)
{
	return (void *)(unsigned long)val;
}

static inline const void *u64_to_const_ptr(__u64 val)
{
	return (const void *)(unsigned long)val;
}

int __btf_obj_id_via_fd(int fd)
{
	struct bpf_btf_info info;
	__u32 len = sizeof(info);
	int err;

	memset(&info, 0, sizeof(info));

	err = bpf_obj_get_info_by_fd(fd, &info, &len); /* Privileged op */
	if (err) {
		pr_err("ERR(%d): Can't get BTF object info on FD(%d): %s\n",
		       errno, fd, strerror(errno));
		return 0;
	}

	return info.id;
}

char * __btf_obj_name_via_fd(int fd)
{
	struct bpf_btf_info info;
	__u32 len = sizeof(info);
	char name[128];
	int err;

	memset(&info, 0, sizeof(info));
	memset(name, 0, sizeof(name));

	info.name_len = sizeof(name);
	info.name = ptr_to_u64(name);

	err = bpf_obj_get_info_by_fd(fd, &info, &len); /* Privileged op */
	if (err) {
		pr_err("ERR(%d): Can't get BTF object info on FD(%d): %s\n",
		       errno, fd, strerror(errno));
		return 0;
	}

	/* Caller must call free() */
	return strndup(name, sizeof(name));
}

int __btf_obj_info_via_fd(int fd, struct bpf_btf_info *info)
{
#define SZ 128
	__u32 len = sizeof(*info);
	char *name;
	int err;

	if (!info)
		return -1;

	/* Caller must call free() */
	name = malloc(SZ);
	if (!name)
		return -ENOMEM;

	memset(name, 0, SZ);
	memset(info, 0, sizeof(*info));

	info->name_len = SZ;
	info->name = ptr_to_u64(name);

	err = bpf_obj_get_info_by_fd(fd, info, &len); /* Privileged op */
	if (err) {
		pr_err("ERR(%d): Can't get BTF object info on FD(%d): %s\n",
		       errno, fd, strerror(errno));
		free(name);
		return 0;
	}

	return info->id;
#undef SZ
}

struct btf *open_vmlinux_btf(void)
{
	struct btf* btf_obj;
	int fd;

	//btf_obj = btf_load_vmlinux_from_kernel();
	btf_obj = btf__load_vmlinux_btf();

	/* *** DOES NOT WORK ***
	 *
	 * The struct btf object returned by btf__load_vmlinux_btf() doesn't
	 * have a file descriptor set we can use.
	 */
	fd = btf__fd(btf_obj);
	if (fd < 0)
		pr_err("WARN: BTF-obj miss FD(%d)\n", fd);

	return btf_obj;
}

int walk_all_ids(void)
{
	__u32 lookup_id, id = 0;
	char *name;
	int err;
	int fd;

	while (true) {
		err = bpf_btf_get_next_id(id, &id);
		if (err) {
			if (errno == ENOENT) {
				err = 0;
				pr_err("No more IDs (last id:%d)\n", id);
				break;
			}
			pr_err("can't get next BTF object: %s%s\n",
			       strerror(errno),
			       errno == EINVAL ? " -- kernel too old?" : "");
			err = -1;
			break;
		}

		fd = bpf_btf_get_fd_by_id(id);
		if (fd < 0) {
			if (errno == ENOENT)
				continue;
			pr_err("can't get BTF object by id (%u): %s",
			       id, strerror(errno));
			err = -1;
			break;
		}

		lookup_id = __btf_obj_id_via_fd(fd);
		name = __btf_obj_name_via_fd(fd);
		printf("Walk id:%d lookup_id:%d name:%s\t\t(FD:%d)\n",
		       id, lookup_id, name, fd);
		free(name);
		close(fd);
	}

	return err;
}

/**
 * find_btf_id_by_name - walks BTFs by incremental ID to find name match
 *
 * @btf_name: Match against this BTF name
 * @btf_size: Ptr to return BTF kernel raw data_size (for subsequent calls)
 *
 * Returns:
 *  Negative number on errors.
 *  Positive number is BTF obj ID.
 *
 */
int find_btf_id_by_name(const char *btf_name, int *btf_size)
{
	struct bpf_btf_info info;
	__u32 id = 0, id2;
	char *name;
	int err;
	int fd;

	while (true) {
		err = bpf_btf_get_next_id(id, &id);
		if (err) {
			if (errno == ENOENT) {
				err = 0;
				pr_err("No more IDs (last id:%d)\n", id);
				break;
			}
			pr_err("can't get next BTF object: %s%s\n",
			       strerror(errno),
			       errno == EINVAL ? " -- kernel too old?" : "");
			err = -1;
			break;
		}

		fd = bpf_btf_get_fd_by_id(id);
		if (fd < 0) {
			if (errno == ENOENT)
				continue;
			pr_err("can't get BTF object by id (%u): %s",
			       id, strerror(errno));
			err = -1;
			break;
		}

		id2 = __btf_obj_info_via_fd(fd, &info);
		if (id2 <= 0) {
			err = -2;
			break;
		}

		if (info.name_len == 0) /* Skip non/empty names */
			continue;

		name = u64_to_ptr(info.name);
		if (strncmp(name, btf_name, 127) == 0) {

			if (btf_size)
				*btf_size = info.btf_size;

			free(name);
			return id;
		}

		//printf("Walk id:%d lookup_id:%d name:%s\t\t(len:%d)\n",
		//       id, id2, name, info.name_len);

		free(name);
		close(fd);
	}

	return err;
}


int main(int argc, char **argv)
{
//	struct btf *vmlinux_btf;
	int opt, longindex = 0;
	int module_btf_id;
	int module_btf_sz;
        int err = 0;


	/* Parse commands line args */
	while ((opt = getopt_long(argc, argv, "dm:",
				  long_options, &longindex)) != -1) {
		switch (opt) {
		case 'd':
			libbpf_set_print(print_all_levels);
			break;
		case 'm': /* --module */
			strncpy(module_name, optarg, sizeof(module_name) - 1);
			break;
		default:
			pr_err("Unrecognized option '%s'\n", argv[optind - 1]);
			return EXIT_FAILURE;
		}
	}
	argc -= optind;
	argv += optind;

//	vmlinux_btf = open_vmlinux_btf();

//	err = walk_all_ids();

	module_btf_id = find_btf_id_by_name(module_name, &module_btf_sz);
	if (module_btf_id > 0) {
		printf("Found BTF object id:%d for module name:%s (data sz:%d)\n",
		       module_btf_id, module_name, module_btf_sz);
	} else {
		pr_err("WARN(%d) - no BTF object ID found for module name: %s\n",
		       module_btf_id, module_name);
	}

//	btf__free(vmlinux_btf);
	if (err)
		return EXIT_FAILURE;
	return EXIT_SUCCESS;
}