// SPDX-License-Identifier: GPL-2.0#include <linux/stringify.h>#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <stdio.h>#include <stdlib.h>#include <string.h>#include "fs.h" struct cgroupfs_cache_entry {	char	subsys[32];	char	mountpoint[PATH_MAX];}; /* just cache last used one */static struct cgroupfs_cache_entry *cached; int cgroupfs_find_mountpoint(char *buf, size_t maxlen, const char *subsys){	FILE *fp;	char *line = NULL;	size_t len = 0;	char *p, *path;	char mountpoint[PATH_MAX]; 	if (cached && !strcmp(cached->subsys, subsys)) {		if (strlen(cached->mountpoint) < maxlen) {			strcpy(buf, cached->mountpoint);			return 0;		}		return -1;	} 	fp = fopen("/proc/mounts", "r");	if (!fp)		return -1; 	/*	 * in order to handle split hierarchy, we need to scan /proc/mounts	 * and inspect every cgroupfs mount point to find one that has	 * the given subsystem.  If we found v1, just use it.  If not we can	 * use v2 path as a fallback.	 */	mountpoint[0] = '\0'; 	/*	 * The /proc/mounts has the follow format:	 *	 *   <devname> <mount point> <fs type> <options> ...	 *	 */	while (getline(&line, &len, fp) != -1) {		/* skip devname */		p = strchr(line, ' ');		if (p == NULL)			continue; 		/* save the mount point */		path = ++p;		p = strchr(p, ' ');		if (p == NULL)			continue; 		*p++ = '\0'; 		/* check filesystem type */		if (strncmp(p, "cgroup", 6))			continue; 		if (p[6] == '2') {			/* save cgroup v2 path */			strcpy(mountpoint, path);			continue;		} 		/* now we have cgroup v1, check the options for subsystem */		p += 7; 		p = strstr(p, subsys);		if (p == NULL)			continue; 		/* sanity check: it should be separated by a space or a comma */		if (!strchr(" ,", p[-1]) || !strchr(" ,", p[strlen(subsys)]))			continue; 		strcpy(mountpoint, path);		break;	}	free(line);	fclose(fp); 	if (!cached)		cached = calloc(1, sizeof(*cached)); 	if (cached) {		strncpy(cached->subsys, subsys, sizeof(cached->subsys) - 1);		strcpy(cached->mountpoint, mountpoint);	} 	if (mountpoint[0] && strlen(mountpoint) < maxlen) {		strcpy(buf, mountpoint);		return 0;	}	return -1;}