src/tracefs-utils.c

// SPDX-License-Identifier: LGPL-2.1
/*
 * Copyright (C) 2008, 2009, 2010 Red Hat Inc, Steven Rostedt <srostedt@redhat.com>
 *
 * Updates:
 * Copyright (C) 2019, VMware, Tzvetomir Stoyanov <tz.stoyanov@gmail.com>
 *
 */
#include <stdlib.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <linux/limits.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>

#include <traceevent/event-utils.h>
#include "tracefs.h"
#include "tracefs-local.h"

#define TRACEFS_PATH "/sys/kernel/tracing"
#define DEBUGFS_PATH "/sys/kernel/debug"

#define _STR(x) #x
#define STR(x) _STR(x)

void __weak tracefs_warning(const char *fmt, ...)
{
	va_list ap;

	va_start(ap, fmt);
	tep_vwarning("libtracefs", fmt, ap);
	va_end(ap);
}

static int mount_tracefs(void)
{
	struct stat st;
	int ret;

	/* make sure debugfs exists */
	ret = stat(TRACEFS_PATH, &st);
	if (ret < 0)
		return -1;

	ret = mount("nodev", TRACEFS_PATH,
		    "tracefs", 0, NULL);

	return ret;
}

static int mount_debugfs(void)
{
	struct stat st;
	int ret;

	/* make sure debugfs exists */
	ret = stat(DEBUGFS_PATH, &st);
	if (ret < 0)
		return -1;

	ret = mount("nodev", DEBUGFS_PATH,
		    "debugfs", 0, NULL);

	return ret;
}

/**
 * trace_find_tracing_dir - Find tracing directory
 *
 * Returns string containing the full path to the system's tracing directory.
 * The string must be freed by free()
 */
__hidden char *trace_find_tracing_dir(void)
{
	char *debug_str = NULL;
	char fspath[PATH_MAX+1];
	char *tracing_dir;
	char type[100];
	int use_debug = 0;
	FILE *fp;

	fp = fopen("/proc/mounts", "r");
	if (!fp) {
		tracefs_warning("Can't open /proc/mounts for read");
		return NULL;
	}

	while (fscanf(fp, "%*s %"
		      STR(PATH_MAX)
		      "s %99s %*s %*d %*d\n",
		      fspath, type) == 2) {
		if (strcmp(type, "tracefs") == 0)
			break;
		if (!debug_str && strcmp(type, "debugfs") == 0) {
			debug_str = strdup(fspath);
			if (!debug_str) {
				fclose(fp);
				return NULL;
			}
		}
	}
	fclose(fp);

	if (strcmp(type, "tracefs") != 0) {
		if (mount_tracefs() < 0) {
			if (debug_str) {
				strncpy(fspath, debug_str, PATH_MAX);
				fspath[PATH_MAX] = 0;
			} else {
				if (mount_debugfs() < 0) {
					tracefs_warning("debugfs not mounted, please mount");
					free(debug_str);
					return NULL;
				}
				strcpy(fspath, DEBUGFS_PATH);
			}
			use_debug = 1;
		} else
			strcpy(fspath, TRACEFS_PATH);
	}
	free(debug_str);

	if (use_debug) {
		int ret;

		ret = asprintf(&tracing_dir, "%s/tracing", fspath);
		if (ret < 0)
			return NULL;
	} else {
		tracing_dir = strdup(fspath);
		if (!tracing_dir)
			return NULL;
	}

	return tracing_dir;
}

/**
 * tracefs_tracing_dir - Get tracing directory
 *
 * Returns string containing the full path to the system's tracing directory.
 * The returned string must *not* be freed.
 */
const char *tracefs_tracing_dir(void)
{
	static const char *tracing_dir;

	if (tracing_dir)
		return tracing_dir;

	tracing_dir = trace_find_tracing_dir();
	return tracing_dir;
}

/**
 * tracefs_get_tracing_file - Get tracing file
 * @name: tracing file name
 *
 * Returns string containing the full path to a tracing file in
 * the system's tracing directory.
 *
 * Must use tracefs_put_tracing_file() to free the returned string.
 */
char *tracefs_get_tracing_file(const char *name)
{
	static const char *tracing;
	char *file;
	int ret;

	if (!name)
		return NULL;

	if (!tracing) {
		tracing = trace_find_tracing_dir();
		if (!tracing)
			return NULL;
	}

	ret = asprintf(&file, "%s/%s", tracing, name);
	if (ret < 0)
		return NULL;

	return file;
}

/**
 * tracefs_put_tracing_file - Free tracing file or directory name
 *
 * Frees tracing file or directory, returned by
 * tracefs_get_tracing_file()API.
 */
void tracefs_put_tracing_file(char *name)
{
	free(name);
}

__hidden int str_read_file(const char *file, char **buffer, bool warn)
{
	char stbuf[BUFSIZ];
	char *buf = NULL;
	int size = 0;
	char *nbuf;
	int fd;
	int r;

	fd = open(file, O_RDONLY);
	if (fd < 0) {
		if (warn)
			tracefs_warning("File %s not found", file);
		return -1;
	}

	do {
		r = read(fd, stbuf, BUFSIZ);
		if (r <= 0)
			continue;
		nbuf = realloc(buf, size+r+1);
		if (!nbuf) {
			if (warn)
				tracefs_warning("Failed to allocate file buffer");
			size = -1;
			break;
		}
		buf = nbuf;
		memcpy(buf+size, stbuf, r);
		size += r;
	} while (r > 0);

	close(fd);
	if (r == 0 && size > 0) {
		buf[size] = '\0';
		*buffer = buf;
	} else
		free(buf);

	return size;
}