Revert "Revert "cgfsng: avoid tiny race window""

[mirror_lxc.git] / src / lxc / cgroups / cgfsng.c

/*
 * lxc: linux Container library
 *
 * Copyright © 2016 Canonical Ltd.
 *
 * Authors:
 * Serge Hallyn <serge.hallyn@ubuntu.com>
 * Christian Brauner <christian.brauner@ubuntu.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/*
 * cgfs-ng.c: this is a new, simplified implementation of a filesystem
 * cgroup backend.  The original cgfs.c was designed to be as flexible
 * as possible.  It would try to find cgroup filesystems no matter where
 * or how you had them mounted, and deduce the most usable mount for
 * each controller.
 *
 * This new implementation assumes that cgroup filesystems are mounted
 * under /sys/fs/cgroup/clist where clist is either the controller, or
 * a comman-separated list of controllers.
 */

#ifndef _GNU_SOURCE
#define _GNU_SOURCE 1
#endif
#include <ctype.h>
#include <dirent.h>
#include <errno.h>
#include <grp.h>
#include <linux/kdev_t.h>
#include <linux/types.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>

#include "caps.h"
#include "cgroup.h"
#include "cgroup_utils.h"
#include "commands.h"
#include "conf.h"
#include "config.h"
#include "log.h"
#include "macro.h"
#include "storage/storage.h"
#include "utils.h"

#ifndef HAVE_STRLCPY
#include "include/strlcpy.h"
#endif

#ifndef HAVE_STRLCAT
#include "include/strlcat.h"
#endif

lxc_log_define(cgfsng, cgroup);

static void free_string_list(char **clist)
{
        int i;

        if (!clist)
                return;

        for (i = 0; clist[i]; i++)
                free(clist[i]);

        free(clist);
}

/* Allocate a pointer, do not fail. */
static void *must_alloc(size_t sz)
{
        return must_realloc(NULL, sz);
}

/* Given a pointer to a null-terminated array of pointers, realloc to add one
 * entry, and point the new entry to NULL. Do not fail. Return the index to the
 * second-to-last entry - that is, the one which is now available for use
 * (keeping the list null-terminated).
 */
static int append_null_to_list(void ***list)
{
        int newentry = 0;

        if (*list)
                for (; (*list)[newentry]; newentry++)
                        ;

        *list = must_realloc(*list, (newentry + 2) * sizeof(void **));
        (*list)[newentry + 1] = NULL;
        return newentry;
}

/* Given a null-terminated array of strings, check whether @entry is one of the
 * strings.
 */
static bool string_in_list(char **list, const char *entry)
{
        int i;

        if (!list)
                return false;

        for (i = 0; list[i]; i++)
                if (strcmp(list[i], entry) == 0)
                        return true;

        return false;
}

/* Return a copy of @entry prepending "name=", i.e.  turn "systemd" into
 * "name=systemd". Do not fail.
 */
static char *cg_legacy_must_prefix_named(char *entry)
{
        size_t len;
        char *prefixed;

        len = strlen(entry);
        prefixed = must_alloc(len + 6);

        memcpy(prefixed, "name=", STRLITERALLEN("name="));
        memcpy(prefixed + STRLITERALLEN("name="), entry, len);
        prefixed[len + 5] = '\0';

        return prefixed;
}

/* Append an entry to the clist. Do not fail. @clist must be NULL the first time
 * we are called.
 *
 * We also handle named subsystems here. Any controller which is not a kernel
 * subsystem, we prefix "name=". Any which is both a kernel and named subsystem,
 * we refuse to use because we're not sure which we have here.
 * (TODO: We could work around this in some cases by just remounting to be
 * unambiguous, or by comparing mountpoint contents with current cgroup.)
 *
 * The last entry will always be NULL.
 */
static void must_append_controller(char **klist, char **nlist, char ***clist,
                                   char *entry)
{
        int newentry;
        char *copy;

        if (string_in_list(klist, entry) && string_in_list(nlist, entry)) {
                ERROR("Refusing to use ambiguous controller \"%s\"", entry);
                ERROR("It is both a named and kernel subsystem");
                return;
        }

        newentry = append_null_to_list((void ***)clist);

        if (strncmp(entry, "name=", 5) == 0)
                copy = must_copy_string(entry);
        else if (string_in_list(klist, entry))
                copy = must_copy_string(entry);
        else
                copy = cg_legacy_must_prefix_named(entry);

        (*clist)[newentry] = copy;
}

/* Given a handler's cgroup data, return the struct hierarchy for the controller
 * @c, or NULL if there is none.
 */
struct hierarchy *get_hierarchy(struct cgroup_ops *ops, const char *controller)
{
        int i;

        errno = ENOENT;

        if (!ops->hierarchies) {
                TRACE("There are no useable cgroup controllers");
                return NULL;
        }

        for (i = 0; ops->hierarchies[i]; i++) {
                if (!controller) {
                        /* This is the empty unified hierarchy. */
                        if (ops->hierarchies[i]->controllers &&
                            !ops->hierarchies[i]->controllers[0])
                                return ops->hierarchies[i];

                        continue;
                }

                if (string_in_list(ops->hierarchies[i]->controllers, controller))
                        return ops->hierarchies[i];
        }

        if (controller)
                WARN("There is no useable %s controller", controller);
        else
                WARN("There is no empty unified cgroup hierarchy");

        return NULL;
}

#define BATCH_SIZE 50
static void batch_realloc(char **mem, size_t oldlen, size_t newlen)
{
        int newbatches = (newlen / BATCH_SIZE) + 1;
        int oldbatches = (oldlen / BATCH_SIZE) + 1;

        if (!*mem || newbatches > oldbatches) {
                *mem = must_realloc(*mem, newbatches * BATCH_SIZE);
        }
}

static void append_line(char **dest, size_t oldlen, char *new, size_t newlen)
{
        size_t full = oldlen + newlen;

        batch_realloc(dest, oldlen, full + 1);

        memcpy(*dest + oldlen, new, newlen + 1);
}

/* Slurp in a whole file */
static char *read_file(const char *fnam)
{
        FILE *f;
        char *line = NULL, *buf = NULL;
        size_t len = 0, fulllen = 0;
        int linelen;

        f = fopen(fnam, "r");
        if (!f)
                return NULL;
        while ((linelen = getline(&line, &len, f)) != -1) {
                append_line(&buf, fulllen, line, linelen);
                fulllen += linelen;
        }
        fclose(f);
        free(line);
        return buf;
}

/* Taken over modified from the kernel sources. */
#define NBITS 32 /* bits in uint32_t */
#define DIV_ROUND_UP(n, d) (((n) + (d)-1) / (d))
#define BITS_TO_LONGS(nr) DIV_ROUND_UP(nr, NBITS)

static void set_bit(unsigned bit, uint32_t *bitarr)
{
        bitarr[bit / NBITS] |= (1 << (bit % NBITS));
}

static void clear_bit(unsigned bit, uint32_t *bitarr)
{
        bitarr[bit / NBITS] &= ~(1 << (bit % NBITS));
}

static bool is_set(unsigned bit, uint32_t *bitarr)
{
        return (bitarr[bit / NBITS] & (1 << (bit % NBITS))) != 0;
}

/* Create cpumask from cpulist aka turn:
 *
 *      0,2-3
 *
 * into bit array
 *
 *      1 0 1 1
 */
static uint32_t *lxc_cpumask(char *buf, size_t nbits)
{
        char *token;
        size_t arrlen;
        uint32_t *bitarr;

        arrlen = BITS_TO_LONGS(nbits);
        bitarr = calloc(arrlen, sizeof(uint32_t));
        if (!bitarr)
                return NULL;

        lxc_iterate_parts(token, buf, ",") {
                errno = 0;
                unsigned end, start;
                char *range;

                start = strtoul(token, NULL, 0);
                end = start;
                range = strchr(token, '-');
                if (range)
                        end = strtoul(range + 1, NULL, 0);

                if (!(start <= end)) {
                        free(bitarr);
                        return NULL;
                }

                if (end >= nbits) {
                        free(bitarr);
                        return NULL;
                }

                while (start <= end)
                        set_bit(start++, bitarr);
        }

        return bitarr;
}

/* Turn cpumask into simple, comma-separated cpulist. */
static char *lxc_cpumask_to_cpulist(uint32_t *bitarr, size_t nbits)
{
        int ret;
        size_t i;
        char **cpulist = NULL;
        char numstr[INTTYPE_TO_STRLEN(size_t)] = {0};

        for (i = 0; i <= nbits; i++) {
                if (!is_set(i, bitarr))
                        continue;

                ret = snprintf(numstr, sizeof(numstr), "%zu", i);
                if (ret < 0 || (size_t)ret >= sizeof(numstr)) {
                        lxc_free_array((void **)cpulist, free);
                        return NULL;
                }

                ret = lxc_append_string(&cpulist, numstr);
                if (ret < 0) {
                        lxc_free_array((void **)cpulist, free);
                        return NULL;
                }
        }

        if (!cpulist)
                return NULL;

        return lxc_string_join(",", (const char **)cpulist, false);
}

static ssize_t get_max_cpus(char *cpulist)
{
        char *c1, *c2;
        char *maxcpus = cpulist;
        size_t cpus = 0;

        c1 = strrchr(maxcpus, ',');
        if (c1)
                c1++;

        c2 = strrchr(maxcpus, '-');
        if (c2)
                c2++;

        if (!c1 && !c2)
                c1 = maxcpus;
        else if (c1 > c2)
                c2 = c1;
        else if (c1 < c2)
                c1 = c2;
        else if (!c1 && c2)
                c1 = c2;

        errno = 0;
        cpus = strtoul(c1, NULL, 0);
        if (errno != 0)
                return -1;

        return cpus;
}

#define __ISOL_CPUS "/sys/devices/system/cpu/isolated"
static bool cg_legacy_filter_and_set_cpus(char *path, bool am_initialized)
{
        int ret;
        ssize_t i;
        char *lastslash, *fpath, oldv;
        ssize_t maxisol = 0, maxposs = 0;
        char *cpulist = NULL, *isolcpus = NULL, *posscpus = NULL;
        uint32_t *isolmask = NULL, *possmask = NULL;
        bool bret = false, flipped_bit = false;

        lastslash = strrchr(path, '/');
        if (!lastslash) {
                ERROR("Failed to detect \"/\" in \"%s\"", path);
                return bret;
        }
        oldv = *lastslash;
        *lastslash = '\0';
        fpath = must_make_path(path, "cpuset.cpus", NULL);
        posscpus = read_file(fpath);
        if (!posscpus) {
                SYSERROR("Failed to read file \"%s\"", fpath);
                goto on_error;
        }

        /* Get maximum number of cpus found in possible cpuset. */
        maxposs = get_max_cpus(posscpus);
        if (maxposs < 0 || maxposs >= INT_MAX - 1)
                goto on_error;

        if (!file_exists(__ISOL_CPUS)) {
                /* This system doesn't expose isolated cpus. */
                DEBUG("The path \""__ISOL_CPUS"\" to read isolated cpus from does not exist");
                cpulist = posscpus;
                /* No isolated cpus but we weren't already initialized by
                 * someone. We should simply copy the parents cpuset.cpus
                 * values.
                 */
                if (!am_initialized) {
                        DEBUG("Copying cpu settings of parent cgroup");
                        goto copy_parent;
                }
                /* No isolated cpus but we were already initialized by someone.
                 * Nothing more to do for us.
                 */
                goto on_success;
        }

        isolcpus = read_file(__ISOL_CPUS);
        if (!isolcpus) {
                SYSERROR("Failed to read file \""__ISOL_CPUS"\"");
                goto on_error;
        }
        if (!isdigit(isolcpus[0])) {
                TRACE("No isolated cpus detected");
                cpulist = posscpus;
                /* No isolated cpus but we weren't already initialized by
                 * someone. We should simply copy the parents cpuset.cpus
                 * values.
                 */
                if (!am_initialized) {
                        DEBUG("Copying cpu settings of parent cgroup");
                        goto copy_parent;
                }
                /* No isolated cpus but we were already initialized by someone.
                 * Nothing more to do for us.
                 */
                goto on_success;
        }

        /* Get maximum number of cpus found in isolated cpuset. */
        maxisol = get_max_cpus(isolcpus);
        if (maxisol < 0 || maxisol >= INT_MAX - 1)
                goto on_error;

        if (maxposs < maxisol)
                maxposs = maxisol;
        maxposs++;

        possmask = lxc_cpumask(posscpus, maxposs);
        if (!possmask) {
                ERROR("Failed to create cpumask for possible cpus");
                goto on_error;
        }

        isolmask = lxc_cpumask(isolcpus, maxposs);
        if (!isolmask) {
                ERROR("Failed to create cpumask for isolated cpus");
                goto on_error;
        }

        for (i = 0; i <= maxposs; i++) {
                if (!is_set(i, isolmask) || !is_set(i, possmask))
                        continue;

                flipped_bit = true;
                clear_bit(i, possmask);
        }

        if (!flipped_bit) {
                DEBUG("No isolated cpus present in cpuset");
                goto on_success;
        }
        DEBUG("Removed isolated cpus from cpuset");

        cpulist = lxc_cpumask_to_cpulist(possmask, maxposs);
        if (!cpulist) {
                ERROR("Failed to create cpu list");
                goto on_error;
        }

copy_parent:
        *lastslash = oldv;
        free(fpath);
        fpath = must_make_path(path, "cpuset.cpus", NULL);
        ret = lxc_write_to_file(fpath, cpulist, strlen(cpulist), false, 0666);
        if (ret < 0) {
                SYSERROR("Failed to write cpu list to \"%s\"", fpath);
                goto on_error;
        }

on_success:
        bret = true;

on_error:
        free(fpath);

        free(isolcpus);
        free(isolmask);

        if (posscpus != cpulist)
                free(posscpus);
        free(possmask);

        free(cpulist);
        return bret;
}

/* Copy contents of parent(@path)/@file to @path/@file */
static bool copy_parent_file(char *path, char *file)
{
        int ret;
        char *fpath, *lastslash, oldv;
        int len = 0;
        char *value = NULL;

        lastslash = strrchr(path, '/');
        if (!lastslash) {
                ERROR("Failed to detect \"/\" in \"%s\"", path);
                return false;
        }
        oldv = *lastslash;
        *lastslash = '\0';
        fpath = must_make_path(path, file, NULL);
        len = lxc_read_from_file(fpath, NULL, 0);
        if (len <= 0)
                goto on_error;

        value = must_alloc(len + 1);
        ret = lxc_read_from_file(fpath, value, len);
        if (ret != len)
                goto on_error;
        free(fpath);

        *lastslash = oldv;
        fpath = must_make_path(path, file, NULL);
        ret = lxc_write_to_file(fpath, value, len, false, 0666);
        if (ret < 0)
                SYSERROR("Failed to write \"%s\" to file \"%s\"", value, fpath);
        free(fpath);
        free(value);
        return ret >= 0;

on_error:
        SYSERROR("Failed to read file \"%s\"", fpath);
        free(fpath);
        free(value);
        return false;
}

/* Initialize the cpuset hierarchy in first directory of @gname and set
 * cgroup.clone_children so that children inherit settings. Since the
 * h->base_path is populated by init or ourselves, we know it is already
 * initialized.
 */
static bool cg_legacy_handle_cpuset_hierarchy(struct hierarchy *h, char *cgname)
{
        int ret;
        char v;
        char *cgpath, *clonechildrenpath, *slash;

        if (!string_in_list(h->controllers, "cpuset"))
                return true;

        if (*cgname == '/')
                cgname++;
        slash = strchr(cgname, '/');
        if (slash)
                *slash = '\0';

        cgpath = must_make_path(h->mountpoint, h->container_base_path, cgname, NULL);
        if (slash)
                *slash = '/';

        ret = mkdir(cgpath, 0755);
        if (ret < 0) {
                if (errno != EEXIST) {
                        SYSERROR("Failed to create directory \"%s\"", cgpath);
                        free(cgpath);
                        return false;
                }
        }

        clonechildrenpath = must_make_path(cgpath, "cgroup.clone_children", NULL);
        /* unified hierarchy doesn't have clone_children */
        if (!file_exists(clonechildrenpath)) {
                free(clonechildrenpath);
                free(cgpath);
                return true;
        }

        ret = lxc_read_from_file(clonechildrenpath, &v, 1);
        if (ret < 0) {
                SYSERROR("Failed to read file \"%s\"", clonechildrenpath);
                free(clonechildrenpath);
                free(cgpath);
                return false;
        }

        /* Make sure any isolated cpus are removed from cpuset.cpus. */
        if (!cg_legacy_filter_and_set_cpus(cgpath, v == '1')) {
                SYSERROR("Failed to remove isolated cpus");
                free(clonechildrenpath);
                free(cgpath);
                return false;
        }

        /* Already set for us by someone else. */
        if (v == '1') {
                DEBUG("\"cgroup.clone_children\" was already set to \"1\"");
                free(clonechildrenpath);
                free(cgpath);
                return true;
        }

        /* copy parent's settings */
        if (!copy_parent_file(cgpath, "cpuset.mems")) {
                SYSERROR("Failed to copy \"cpuset.mems\" settings");
                free(cgpath);
                free(clonechildrenpath);
                return false;
        }
        free(cgpath);

        ret = lxc_write_to_file(clonechildrenpath, "1", 1, false, 0666);
        if (ret < 0) {
                /* Set clone_children so children inherit our settings */
                SYSERROR("Failed to write 1 to \"%s\"", clonechildrenpath);
                free(clonechildrenpath);
                return false;
        }
        free(clonechildrenpath);
        return true;
}

/* Given two null-terminated lists of strings, return true if any string is in
 * both.
 */
static bool controller_lists_intersect(char **l1, char **l2)
{
        int i;

        if (!l1 || !l2)
                return false;

        for (i = 0; l1[i]; i++) {
                if (string_in_list(l2, l1[i]))
                        return true;
        }

        return false;
}

/* For a null-terminated list of controllers @clist, return true if any of those
 * controllers is already listed the null-terminated list of hierarchies @hlist.
 * Realistically, if one is present, all must be present.
 */
static bool controller_list_is_dup(struct hierarchy **hlist, char **clist)
{
        int i;

        if (!hlist)
                return false;

        for (i = 0; hlist[i]; i++)
                if (controller_lists_intersect(hlist[i]->controllers, clist))
                        return true;

        return false;
}

/* Return true if the controller @entry is found in the null-terminated list of
 * hierarchies @hlist.
 */
static bool controller_found(struct hierarchy **hlist, char *entry)
{
        int i;

        if (!hlist)
                return false;

        for (i = 0; hlist[i]; i++)
                if (string_in_list(hlist[i]->controllers, entry))
                        return true;

        return false;
}

/* Return true if all of the controllers which we require have been found.  The
 * required list is  freezer and anything in lxc.cgroup.use.
 */
static bool all_controllers_found(struct cgroup_ops *ops)
{
        char **cur;
        struct hierarchy **hlist = ops->hierarchies;

        if (!controller_found(hlist, "freezer")) {
                ERROR("No freezer controller mountpoint found");
                return false;
        }

        if (!ops->cgroup_use)
                return true;

        for (cur = ops->cgroup_use; cur && *cur; cur++)
                if (!controller_found(hlist, *cur)) {
                        ERROR("No %s controller mountpoint found", *cur);
                        return false;
                }

        return true;
}

/* Get the controllers from a mountinfo line There are other ways we could get
 * this info. For lxcfs, field 3 is /cgroup/controller-list. For cgroupfs, we
 * could parse the mount options. But we simply assume that the mountpoint must
 * be /sys/fs/cgroup/controller-list
 */
static char **cg_hybrid_get_controllers(char **klist, char **nlist, char *line,
                                        int type)
{
        /* The fourth field is /sys/fs/cgroup/comma-delimited-controller-list
         * for legacy hierarchies.
         */
        int i;
        char *dup, *p2, *tok;
        char *p = line, *sep = ",";
        char **aret = NULL;

        for (i = 0; i < 4; i++) {
                p = strchr(p, ' ');
                if (!p)
                        return NULL;
                p++;
        }

        /* Note, if we change how mountinfo works, then our caller will need to
         * verify /sys/fs/cgroup/ in this field.
         */
        if (strncmp(p, "/sys/fs/cgroup/", 15) != 0) {
                ERROR("Found hierarchy not under /sys/fs/cgroup: \"%s\"", p);
                return NULL;
        }

        p += 15;
        p2 = strchr(p, ' ');
        if (!p2) {
                ERROR("Corrupt mountinfo");
                return NULL;
        }
        *p2 = '\0';

        if (type == CGROUP_SUPER_MAGIC) {
                /* strdup() here for v1 hierarchies. Otherwise
                 * lxc_iterate_parts() will destroy mountpoints such as
                 * "/sys/fs/cgroup/cpu,cpuacct".
                 */
                dup = strdup(p);
                if (!dup)
                        return NULL;

                lxc_iterate_parts(tok, dup, sep) {
                        must_append_controller(klist, nlist, &aret, tok);
                }

                free(dup);
        }
        *p2 = ' ';

        return aret;
}

static char **cg_unified_make_empty_controller(void)
{
        int newentry;
        char **aret = NULL;

        newentry = append_null_to_list((void ***)&aret);
        aret[newentry] = NULL;
        return aret;
}

static char **cg_unified_get_controllers(const char *file)
{
        char *buf, *tok;
        char *sep = " \t\n";
        char **aret = NULL;

        buf = read_file(file);
        if (!buf)
                return NULL;

        lxc_iterate_parts(tok, buf, sep) {
                int newentry;
                char *copy;

                newentry = append_null_to_list((void ***)&aret);
                copy = must_copy_string(tok);
                aret[newentry] = copy;
        }

        free(buf);
        return aret;
}

static struct hierarchy *add_hierarchy(struct hierarchy ***h, char **clist, char *mountpoint,
                                       char *container_base_path, int type)
{
        struct hierarchy *new;
        int newentry;

        new = must_alloc(sizeof(*new));
        new->controllers = clist;
        new->mountpoint = mountpoint;
        new->container_base_path = container_base_path;
        new->container_full_path = NULL;
        new->monitor_full_path = NULL;
        new->version = type;

        newentry = append_null_to_list((void ***)h);
        (*h)[newentry] = new;
        return new;
}

/* Get a copy of the mountpoint from @line, which is a line from
 * /proc/self/mountinfo.
 */
static char *cg_hybrid_get_mountpoint(char *line)
{
        int i;
        size_t len;
        char *p2;
        char *p = line, *sret = NULL;

        for (i = 0; i < 4; i++) {
                p = strchr(p, ' ');
                if (!p)
                        return NULL;
                p++;
        }

        if (strncmp(p, "/sys/fs/cgroup/", 15) != 0)
                return NULL;

        p2 = strchr(p + 15, ' ');
        if (!p2)
                return NULL;
        *p2 = '\0';

        len = strlen(p);
        sret = must_alloc(len + 1);
        memcpy(sret, p, len);
        sret[len] = '\0';
        return sret;
}

/* Given a multi-line string, return a null-terminated copy of the current line. */
static char *copy_to_eol(char *p)
{
        char *p2 = strchr(p, '\n'), *sret;
        size_t len;

        if (!p2)
                return NULL;

        len = p2 - p;
        sret = must_alloc(len + 1);
        memcpy(sret, p, len);
        sret[len] = '\0';
        return sret;
}

/* cgline: pointer to character after the first ':' in a line in a \n-terminated
 * /proc/self/cgroup file. Check whether controller c is present.
 */
static bool controller_in_clist(char *cgline, char *c)
{
        char *tok, *eol, *tmp;
        size_t len;

        eol = strchr(cgline, ':');
        if (!eol)
                return false;

        len = eol - cgline;
        tmp = alloca(len + 1);
        memcpy(tmp, cgline, len);
        tmp[len] = '\0';

        lxc_iterate_parts(tok, tmp, ",") {
                if (strcmp(tok, c) == 0)
                        return true;
        }

        return false;
}

/* @basecginfo is a copy of /proc/$$/cgroup. Return the current cgroup for
 * @controller.
 */
static char *cg_hybrid_get_current_cgroup(char *basecginfo, char *controller,
                                          int type)
{
        char *p = basecginfo;

        for (;;) {
                bool is_cgv2_base_cgroup = false;

                /* cgroup v2 entry in "/proc/<pid>/cgroup": "0::/some/path" */
                if ((type == CGROUP2_SUPER_MAGIC) && (*p == '0'))
                        is_cgv2_base_cgroup = true;

                p = strchr(p, ':');
                if (!p)
                        return NULL;
                p++;

                if (is_cgv2_base_cgroup || (controller && controller_in_clist(p, controller))) {
                        p = strchr(p, ':');
                        if (!p)
                                return NULL;
                        p++;
                        return copy_to_eol(p);
                }

                p = strchr(p, '\n');
                if (!p)
                        return NULL;
                p++;
        }
}

static void must_append_string(char ***list, char *entry)
{
        int newentry;
        char *copy;

        newentry = append_null_to_list((void ***)list);
        copy = must_copy_string(entry);
        (*list)[newentry] = copy;
}

static int get_existing_subsystems(char ***klist, char ***nlist)
{
        FILE *f;
        char *line = NULL;
        size_t len = 0;

        f = fopen("/proc/self/cgroup", "r");
        if (!f)
                return -1;

        while (getline(&line, &len, f) != -1) {
                char *p, *p2, *tok;
                p = strchr(line, ':');
                if (!p)
                        continue;
                p++;
                p2 = strchr(p, ':');
                if (!p2)
                        continue;
                *p2 = '\0';

                /* If the kernel has cgroup v2 support, then /proc/self/cgroup
                 * contains an entry of the form:
                 *
                 *      0::/some/path
                 *
                 * In this case we use "cgroup2" as controller name.
                 */
                if ((p2 - p) == 0) {
                        must_append_string(klist, "cgroup2");
                        continue;
                }

                lxc_iterate_parts(tok, p, ",") {
                        if (strncmp(tok, "name=", 5) == 0)
                                must_append_string(nlist, tok);
                        else
                                must_append_string(klist, tok);
                }
        }

        free(line);
        fclose(f);
        return 0;
}

static void trim(char *s)
{
        size_t len;

        len = strlen(s);
        while ((len > 1) && (s[len - 1] == '\n'))
                s[--len] = '\0';
}

static void lxc_cgfsng_print_hierarchies(struct cgroup_ops *ops)
{
        int i;
        struct hierarchy **it;

        if (!ops->hierarchies) {
                TRACE("  No hierarchies found");
                return;
        }

        TRACE("  Hierarchies:");
        for (i = 0, it = ops->hierarchies; it && *it; it++, i++) {
                int j;
                char **cit;

                TRACE("  %d: base_cgroup: %s", i, (*it)->container_base_path ? (*it)->container_base_path : "(null)");
                TRACE("      mountpoint:  %s", (*it)->mountpoint ? (*it)->mountpoint : "(null)");
                TRACE("      controllers:");
                for (j = 0, cit = (*it)->controllers; cit && *cit; cit++, j++)
                        TRACE("      %d: %s", j, *cit);
        }
}

static void lxc_cgfsng_print_basecg_debuginfo(char *basecginfo, char **klist,
                                              char **nlist)
{
        int k;
        char **it;

        TRACE("basecginfo is:");
        TRACE("%s", basecginfo);

        for (k = 0, it = klist; it && *it; it++, k++)
                TRACE("kernel subsystem %d: %s", k, *it);

        for (k = 0, it = nlist; it && *it; it++, k++)
                TRACE("named subsystem %d: %s", k, *it);
}

static int cgroup_rmdir(struct hierarchy **hierarchies,
                        const char *container_cgroup)
{
        int i;

        if (!container_cgroup || !hierarchies)
                return 0;

        for (i = 0; hierarchies[i]; i++) {
                int ret;
                struct hierarchy *h = hierarchies[i];

                if (!h->container_full_path)
                        continue;

                ret = recursive_destroy(h->container_full_path);
                if (ret < 0)
                        WARN("Failed to destroy \"%s\"", h->container_full_path);

                free(h->container_full_path);
                h->container_full_path = NULL;
        }

        return 0;
}

struct generic_userns_exec_data {
        struct hierarchy **hierarchies;
        const char *container_cgroup;
        struct lxc_conf *conf;
        uid_t origuid; /* target uid in parent namespace */
        char *path;
};

static int cgroup_rmdir_wrapper(void *data)
{
        int ret;
        struct generic_userns_exec_data *arg = data;
        uid_t nsuid = (arg->conf->root_nsuid_map != NULL) ? 0 : arg->conf->init_uid;
        gid_t nsgid = (arg->conf->root_nsgid_map != NULL) ? 0 : arg->conf->init_gid;

        ret = setresgid(nsgid, nsgid, nsgid);
        if (ret < 0) {
                SYSERROR("Failed to setresgid(%d, %d, %d)", (int)nsgid,
                         (int)nsgid, (int)nsgid);
                return -1;
        }

        ret = setresuid(nsuid, nsuid, nsuid);
        if (ret < 0) {
                SYSERROR("Failed to setresuid(%d, %d, %d)", (int)nsuid,
                         (int)nsuid, (int)nsuid);
                return -1;
        }

        ret = setgroups(0, NULL);
        if (ret < 0 && errno != EPERM) {
                SYSERROR("Failed to setgroups(0, NULL)");
                return -1;
        }

        return cgroup_rmdir(arg->hierarchies, arg->container_cgroup);
}

__cgfsng_ops static void cgfsng_payload_destroy(struct cgroup_ops *ops,
                                                struct lxc_handler *handler)
{
        int ret;
        struct generic_userns_exec_data wrap;

        wrap.origuid = 0;
        wrap.container_cgroup = ops->container_cgroup;
        wrap.hierarchies = ops->hierarchies;
        wrap.conf = handler->conf;

        if (handler->conf && !lxc_list_empty(&handler->conf->id_map))
                ret = userns_exec_1(handler->conf, cgroup_rmdir_wrapper, &wrap,
                                    "cgroup_rmdir_wrapper");
        else
                ret = cgroup_rmdir(ops->hierarchies, ops->container_cgroup);
        if (ret < 0) {
                WARN("Failed to destroy cgroups");
                return;
        }
}

__cgfsng_ops static void cgfsng_monitor_destroy(struct cgroup_ops *ops,
                                                struct lxc_handler *handler)
{
        int len;
        char *pivot_path;
        struct lxc_conf *conf = handler->conf;
        char pidstr[INTTYPE_TO_STRLEN(pid_t)];

        if (!ops->hierarchies)
                return;

        len = snprintf(pidstr, sizeof(pidstr), "%d", handler->monitor_pid);
        if (len < 0 || (size_t)len >= sizeof(pidstr))
                return;

        for (int i = 0; ops->hierarchies[i]; i++) {
                int ret;
                struct hierarchy *h = ops->hierarchies[i];

                if (!h->monitor_full_path)
                        continue;

                if (conf && conf->cgroup_meta.dir)
                        pivot_path = must_make_path(h->mountpoint,
                                                    h->container_base_path,
                                                    conf->cgroup_meta.dir,
                                                    PIVOT_CGROUP,
                                                    "cgroup.procs", NULL);
                else
                        pivot_path = must_make_path(h->mountpoint,
                                                    h->container_base_path,
                                                    PIVOT_CGROUP,
                                                    "cgroup.procs", NULL);

                ret = mkdir_p(pivot_path, 0755);
                if (ret < 0 && errno != EEXIST)
                        goto next;

                /* Move ourselves into the pivot cgroup to delete our own
                 * cgroup.
                 */
                ret = lxc_write_to_file(pivot_path, pidstr, len, false, 0666);
                if (ret != 0)
                        goto next;

                ret = recursive_destroy(h->monitor_full_path);
                if (ret < 0)
                        WARN("Failed to destroy \"%s\"", h->monitor_full_path);

        next:
                free(pivot_path);
        }
}

static bool cg_unified_create_cgroup(struct hierarchy *h, char *cgname)
{
        size_t i, parts_len;
        char **it;
        size_t full_len = 0;
        char *add_controllers = NULL, *cgroup = NULL;
        char **parts = NULL;
        bool bret = false;

        if (h->version != CGROUP2_SUPER_MAGIC)
                return true;

        if (!h->controllers)
                return true;

        /* For now we simply enable all controllers that we have detected by
         * creating a string like "+memory +pids +cpu +io".
         * TODO: In the near future we might want to support "-<controller>"
         * etc. but whether supporting semantics like this make sense will need
         * some thinking.
         */
        for (it = h->controllers; it && *it; it++) {
                full_len += strlen(*it) + 2;
                add_controllers = must_realloc(add_controllers, full_len + 1);

                if (h->controllers[0] == *it)
                        add_controllers[0] = '\0';

                (void)strlcat(add_controllers, "+", full_len + 1);
                (void)strlcat(add_controllers, *it, full_len + 1);

                if ((it + 1) && *(it + 1))
                        (void)strlcat(add_controllers, " ", full_len + 1);
        }

        parts = lxc_string_split(cgname, '/');
        if (!parts)
                goto on_error;

        parts_len = lxc_array_len((void **)parts);
        if (parts_len > 0)
                parts_len--;

        cgroup = must_make_path(h->mountpoint, h->container_base_path, NULL);
        for (i = 0; i < parts_len; i++) {
                int ret;
                char *target;

                cgroup = must_append_path(cgroup, parts[i], NULL);
                target = must_make_path(cgroup, "cgroup.subtree_control", NULL);
                ret = lxc_write_to_file(target, add_controllers, full_len, false, 0666);
                free(target);
                if (ret < 0) {
                        SYSERROR("Could not enable \"%s\" controllers in the "
                                 "unified cgroup \"%s\"", add_controllers, cgroup);
                        goto on_error;
                }
        }

        bret = true;

on_error:
        lxc_free_array((void **)parts, free);
        free(add_controllers);
        free(cgroup);
        return bret;
}

static int mkdir_eexist_on_last(const char *dir, mode_t mode)
{
        const char *tmp = dir;
        const char *orig = dir;
        size_t orig_len;

        orig_len = strlen(dir);
        do {
                int ret;
                size_t cur_len;
                char *makeme;

                dir = tmp + strspn(tmp, "/");
                tmp = dir + strcspn(dir, "/");

                errno = ENOMEM;
                cur_len = dir - orig;
                makeme = strndup(orig, cur_len);
                if (!makeme)
                        return -1;

                ret = mkdir(makeme, mode);
                if (ret < 0) {
                        if ((errno != EEXIST) || (orig_len == cur_len)) {
                                SYSERROR("Failed to create directory \"%s\"", makeme);
                                free(makeme);
                                return -1;
                        }
                }
                free(makeme);

        } while (tmp != dir);

        return 0;
}

static bool monitor_create_path_for_hierarchy(struct hierarchy *h, char *cgname)
{
        int ret;

        h->monitor_full_path = must_make_path(h->mountpoint, h->container_base_path, cgname, NULL);
        ret = mkdir_eexist_on_last(h->monitor_full_path, 0755);
        if (ret < 0) {
                ERROR("Failed to create cgroup \"%s\"", h->monitor_full_path);
                return false;
        }

        if (!cg_legacy_handle_cpuset_hierarchy(h, cgname)) {
                ERROR("Failed to handle legacy cpuset controller");
                return false;
        }

        return cg_unified_create_cgroup(h, cgname);
}

static bool container_create_path_for_hierarchy(struct hierarchy *h, char *cgname)
{
        int ret;

        h->container_full_path = must_make_path(h->mountpoint, h->container_base_path, cgname, NULL);
        ret = mkdir_eexist_on_last(h->container_full_path, 0755);
        if (ret < 0) {
                ERROR("Failed to create cgroup \"%s\"", h->container_full_path);
                return false;
        }

        if (!cg_legacy_handle_cpuset_hierarchy(h, cgname)) {
                ERROR("Failed to handle legacy cpuset controller");
                return false;
        }

        return cg_unified_create_cgroup(h, cgname);
}

static void remove_path_for_hierarchy(struct hierarchy *h, char *cgname, bool monitor)
{
        int ret;
        char *full_path;

        if (monitor)
                full_path = h->monitor_full_path;
        else
                full_path = h->container_full_path;

        ret = rmdir(full_path);
        if (ret < 0)
                SYSERROR("Failed to rmdir(\"%s\") from failed creation attempt", full_path);

        free(full_path);

        if (monitor)
                h->monitor_full_path = NULL;
        else
                h->container_full_path = NULL;
}

__cgfsng_ops static inline bool cgfsng_monitor_create(struct cgroup_ops *ops,
                                                        struct lxc_handler *handler)
{
        char *monitor_cgroup, *offset, *tmp;
        int i, idx = 0;
        size_t len;
        bool bret = false;
        struct lxc_conf *conf = handler->conf;

        if (!conf)
                return bret;

        if (conf->cgroup_meta.dir)
                tmp = lxc_string_join("/",
                                      (const char *[]){conf->cgroup_meta.dir,
                                                       ops->monitor_pattern,
                                                       handler->name, NULL},
                                      false);
        else
                tmp = must_make_path(ops->monitor_pattern, handler->name, NULL);
        if (!tmp)
                return bret;

        len = strlen(tmp) + 5; /* leave room for -NNN\0 */
        monitor_cgroup = must_alloc(len);
        (void)strlcpy(monitor_cgroup, tmp, len);
        free(tmp);
        offset = monitor_cgroup + len - 5;

        do {
                if (idx) {
                        int ret = snprintf(offset, 5, "-%d", idx);
                        if (ret < 0 || (size_t)ret >= 5)
                                goto on_error;
                }

                for (i = 0; ops->hierarchies[i]; i++) {
                        if (!monitor_create_path_for_hierarchy(ops->hierarchies[i], monitor_cgroup)) {
                                ERROR("Failed to create cgroup \"%s\"", ops->hierarchies[i]->monitor_full_path);
                                free(ops->hierarchies[i]->container_full_path);
                                ops->hierarchies[i]->container_full_path = NULL;

                                for (int j = 0; j < i; j++)
                                        remove_path_for_hierarchy(ops->hierarchies[j], monitor_cgroup, true);

                                idx++;
                                break;
                        }
                }
        } while (ops->hierarchies[i] && idx > 0 && idx < 1000);

        if (idx < 1000) {
                bret = true;
                INFO("The monitor process uses \"%s\" as cgroup", monitor_cgroup);
        }

on_error:
        free(monitor_cgroup);

        return bret;
}

/* Try to create the same cgroup in all hierarchies. Start with cgroup_pattern;
 * next cgroup_pattern-1, -2, ..., -999.
 */
__cgfsng_ops static inline bool cgfsng_payload_create(struct cgroup_ops *ops,
                                                        struct lxc_handler *handler)
{
        int i;
        size_t len;
        char *container_cgroup, *offset, *tmp;
        int idx = 0;
        struct lxc_conf *conf = handler->conf;

        if (ops->container_cgroup) {
                WARN("cgfsng_create called a second time: %s", ops->container_cgroup);
                return false;
        }

        if (!conf)
                return false;

        if (conf->cgroup_meta.dir)
                tmp = lxc_string_join("/", (const char *[]){conf->cgroup_meta.dir, handler->name, NULL}, false);
        else
                tmp = lxc_string_replace("%n", handler->name, ops->cgroup_pattern);
        if (!tmp) {
                ERROR("Failed expanding cgroup name pattern");
                return false;
        }

        len = strlen(tmp) + 5; /* leave room for -NNN\0 */
        container_cgroup = must_alloc(len);
        (void)strlcpy(container_cgroup, tmp, len);
        free(tmp);
        offset = container_cgroup + len - 5;

again:
        if (idx == 1000) {
                ERROR("Too many conflicting cgroup names");
                goto out_free;
        }

        if (idx) {
                int ret;

                ret = snprintf(offset, 5, "-%d", idx);
                if (ret < 0 || (size_t)ret >= 5) {
                        FILE *f = fopen("/dev/null", "w");
                        if (f) {
                                fprintf(f, "Workaround for GCC7 bug: "
                                           "https://gcc.gnu.org/bugzilla/"
                                           "show_bug.cgi?id=78969");
                                fclose(f);
                        }
                }
        }

        for (i = 0; ops->hierarchies[i]; i++) {
                if (!container_create_path_for_hierarchy(ops->hierarchies[i], container_cgroup)) {
                        ERROR("Failed to create cgroup \"%s\"", ops->hierarchies[i]->container_full_path);
                        free(ops->hierarchies[i]->container_full_path);
                        ops->hierarchies[i]->container_full_path = NULL;
                        for (int j = 0; j < i; j++)
                                remove_path_for_hierarchy(ops->hierarchies[j], container_cgroup, false);
                        idx++;
                        goto again;
                }
        }

        ops->container_cgroup = container_cgroup;
        INFO("The container uses \"%s\" as cgroup", container_cgroup);

        return true;

out_free:
        free(container_cgroup);

        return false;
}

__cgfsng_ops static bool __do_cgroup_enter(struct cgroup_ops *ops, pid_t pid,
                                             bool monitor)
{
        int len;
        char pidstr[INTTYPE_TO_STRLEN(pid_t)];

        len = snprintf(pidstr, sizeof(pidstr), "%d", pid);
        if (len < 0 || (size_t)len >= sizeof(pidstr))
                return false;

        for (int i = 0; ops->hierarchies[i]; i++) {
                int ret;
                char *path;

                if (monitor)
                        path = must_make_path(ops->hierarchies[i]->monitor_full_path,
                                              "cgroup.procs", NULL);
                else
                        path = must_make_path(ops->hierarchies[i]->container_full_path,
                                              "cgroup.procs", NULL);
                ret = lxc_write_to_file(path, pidstr, len, false, 0666);
                if (ret != 0) {
                        SYSERROR("Failed to enter cgroup \"%s\"", path);
                        free(path);
                        return false;
                }
                free(path);
        }

        return true;
}

__cgfsng_ops static bool cgfsng_monitor_enter(struct cgroup_ops *ops, pid_t pid)
{
        return __do_cgroup_enter(ops, pid, true);
}

static bool cgfsng_payload_enter(struct cgroup_ops *ops, pid_t pid)
{
        return __do_cgroup_enter(ops, pid, false);
}

static int chowmod(char *path, uid_t chown_uid, gid_t chown_gid,
                   mode_t chmod_mode)
{
        int ret;

        ret = chown(path, chown_uid, chown_gid);
        if (ret < 0) {
                SYSWARN("Failed to chown(%s, %d, %d)", path, (int)chown_uid, (int)chown_gid);
                return -1;
        }

        ret = chmod(path, chmod_mode);
        if (ret < 0) {
                SYSWARN("Failed to chmod(%s, %d)", path, (int)chmod_mode);
                return -1;
        }

        return 0;
}

/* chgrp the container cgroups to container group.  We leave
 * the container owner as cgroup owner.  So we must make the
 * directories 775 so that the container can create sub-cgroups.
 *
 * Also chown the tasks and cgroup.procs files.  Those may not
 * exist depending on kernel version.
 */
static int chown_cgroup_wrapper(void *data)
{
        int i, ret;
        uid_t destuid;
        struct generic_userns_exec_data *arg = data;
        uid_t nsuid = (arg->conf->root_nsuid_map != NULL) ? 0 : arg->conf->init_uid;
        gid_t nsgid = (arg->conf->root_nsgid_map != NULL) ? 0 : arg->conf->init_gid;

        ret = setresgid(nsgid, nsgid, nsgid);
        if (ret < 0) {
                SYSERROR("Failed to setresgid(%d, %d, %d)",
                         (int)nsgid, (int)nsgid, (int)nsgid);
                return -1;
        }

        ret = setresuid(nsuid, nsuid, nsuid);
        if (ret < 0) {
                SYSERROR("Failed to setresuid(%d, %d, %d)",
                         (int)nsuid, (int)nsuid, (int)nsuid);
                return -1;
        }

        ret = setgroups(0, NULL);
        if (ret < 0 && errno != EPERM) {
                SYSERROR("Failed to setgroups(0, NULL)");
                return -1;
        }

        destuid = get_ns_uid(arg->origuid);
        if (destuid == LXC_INVALID_UID)
                destuid = 0;

        for (i = 0; arg->hierarchies[i]; i++) {
                char *fullpath;
                char *path = arg->hierarchies[i]->container_full_path;

                ret = chowmod(path, destuid, nsgid, 0775);
                if (ret < 0)
                        return -1;

                /* Failures to chown() these are inconvenient but not
                 * detrimental We leave these owned by the container launcher,
                 * so that container root can write to the files to attach.  We
                 * chmod() them 664 so that container systemd can write to the
                 * files (which systemd in wily insists on doing).
                 */

                if (arg->hierarchies[i]->version == CGROUP_SUPER_MAGIC) {
                        fullpath = must_make_path(path, "tasks", NULL);
                        (void)chowmod(fullpath, destuid, nsgid, 0664);
                        free(fullpath);
                }

                fullpath = must_make_path(path, "cgroup.procs", NULL);
                (void)chowmod(fullpath, destuid, nsgid, 0664);
                free(fullpath);

                if (arg->hierarchies[i]->version != CGROUP2_SUPER_MAGIC)
                        continue;

                fullpath = must_make_path(path, "cgroup.subtree_control", NULL);
                (void)chowmod(fullpath, destuid, nsgid, 0664);
                free(fullpath);

                fullpath = must_make_path(path, "cgroup.threads", NULL);
                (void)chowmod(fullpath, destuid, nsgid, 0664);
                free(fullpath);
        }

        return 0;
}

__cgfsng_ops static bool cgfsng_chown(struct cgroup_ops *ops,
                                        struct lxc_conf *conf)
{
        struct generic_userns_exec_data wrap;

        if (lxc_list_empty(&conf->id_map))
                return true;

        wrap.origuid = geteuid();
        wrap.path = NULL;
        wrap.hierarchies = ops->hierarchies;
        wrap.conf = conf;

        if (userns_exec_1(conf, chown_cgroup_wrapper, &wrap,
                          "chown_cgroup_wrapper") < 0) {
                ERROR("Error requesting cgroup chown in new user namespace");
                return false;
        }

        return true;
}

/* cgroup-full:* is done, no need to create subdirs */
static bool cg_mount_needs_subdirs(int type)
{
        if (type >= LXC_AUTO_CGROUP_FULL_RO)
                return false;

        return true;
}

/* After $rootfs/sys/fs/container/controller/the/cg/path has been created,
 * remount controller ro if needed and bindmount the cgroupfs onto
 * controll/the/cg/path.
 */
static int cg_legacy_mount_controllers(int type, struct hierarchy *h,
                                       char *controllerpath, char *cgpath,
                                       const char *container_cgroup)
{
        int ret, remount_flags;
        char *sourcepath;
        int flags = MS_BIND;

        if (type == LXC_AUTO_CGROUP_RO || type == LXC_AUTO_CGROUP_MIXED) {
                ret = mount(controllerpath, controllerpath, "cgroup", MS_BIND, NULL);
                if (ret < 0) {
                        SYSERROR("Failed to bind mount \"%s\" onto \"%s\"",
                                 controllerpath, controllerpath);
                        return -1;
                }

                remount_flags = add_required_remount_flags(controllerpath,
                                                           controllerpath,
                                                           flags | MS_REMOUNT);
                ret = mount(controllerpath, controllerpath, "cgroup",
                            remount_flags | MS_REMOUNT | MS_BIND | MS_RDONLY,
                            NULL);
                if (ret < 0) {
                        SYSERROR("Failed to remount \"%s\" ro", controllerpath);
                        return -1;
                }

                INFO("Remounted %s read-only", controllerpath);
        }

        sourcepath = must_make_path(h->mountpoint, h->container_base_path,
                                    container_cgroup, NULL);
        if (type == LXC_AUTO_CGROUP_RO)
                flags |= MS_RDONLY;

        ret = mount(sourcepath, cgpath, "cgroup", flags, NULL);
        if (ret < 0) {
                SYSERROR("Failed to mount \"%s\" onto \"%s\"", h->controllers[0], cgpath);
                free(sourcepath);
                return -1;
        }
        INFO("Mounted \"%s\" onto \"%s\"", h->controllers[0], cgpath);

        if (flags & MS_RDONLY) {
                remount_flags = add_required_remount_flags(sourcepath, cgpath,
                                                           flags | MS_REMOUNT);
                ret = mount(sourcepath, cgpath, "cgroup", remount_flags, NULL);
                if (ret < 0) {
                        SYSERROR("Failed to remount \"%s\" ro", cgpath);
                        free(sourcepath);
                        return -1;
                }
                INFO("Remounted %s read-only", cgpath);
        }

        free(sourcepath);
        INFO("Completed second stage cgroup automounts for \"%s\"", cgpath);
        return 0;
}

/* __cg_mount_direct
 *
 * Mount cgroup hierarchies directly without using bind-mounts. The main
 * uses-cases are mounting cgroup hierarchies in cgroup namespaces and mounting
 * cgroups for the LXC_AUTO_CGROUP_FULL option.
 */
static int __cg_mount_direct(int type, struct hierarchy *h,
                             const char *controllerpath)
{
         int ret;
         char *controllers = NULL;
         char *fstype = "cgroup2";
         unsigned long flags = 0;

         flags |= MS_NOSUID;
         flags |= MS_NOEXEC;
         flags |= MS_NODEV;
         flags |= MS_RELATIME;

         if (type == LXC_AUTO_CGROUP_RO || type == LXC_AUTO_CGROUP_FULL_RO)
                 flags |= MS_RDONLY;

         if (h->version != CGROUP2_SUPER_MAGIC) {
                 controllers = lxc_string_join(",", (const char **)h->controllers, false);
                 if (!controllers)
                         return -ENOMEM;
                 fstype = "cgroup";
        }

        ret = mount("cgroup", controllerpath, fstype, flags, controllers);
        free(controllers);
        if (ret < 0) {
                SYSERROR("Failed to mount \"%s\" with cgroup filesystem type %s", controllerpath, fstype);
                return -1;
        }

        DEBUG("Mounted \"%s\" with cgroup filesystem type %s", controllerpath, fstype);
        return 0;
}

static inline int cg_mount_in_cgroup_namespace(int type, struct hierarchy *h,
                                               const char *controllerpath)
{
        return __cg_mount_direct(type, h, controllerpath);
}

static inline int cg_mount_cgroup_full(int type, struct hierarchy *h,
                                       const char *controllerpath)
{
        if (type < LXC_AUTO_CGROUP_FULL_RO || type > LXC_AUTO_CGROUP_FULL_MIXED)
                return 0;

        return __cg_mount_direct(type, h, controllerpath);
}

__cgfsng_ops static bool cgfsng_mount(struct cgroup_ops *ops,
                                        struct lxc_handler *handler,
                                        const char *root, int type)
{
        int i, ret;
        char *tmpfspath = NULL;
        bool has_cgns = false, retval = false, wants_force_mount = false;

        if ((type & LXC_AUTO_CGROUP_MASK) == 0)
                return true;

        if (type & LXC_AUTO_CGROUP_FORCE) {
                type &= ~LXC_AUTO_CGROUP_FORCE;
                wants_force_mount = true;
        }

        if (!wants_force_mount){
                if (!lxc_list_empty(&handler->conf->keepcaps))
                        wants_force_mount = !in_caplist(CAP_SYS_ADMIN, &handler->conf->keepcaps);
                else
                        wants_force_mount = in_caplist(CAP_SYS_ADMIN, &handler->conf->caps);
        }

        has_cgns = cgns_supported();
        if (has_cgns && !wants_force_mount)
                return true;

        if (type == LXC_AUTO_CGROUP_NOSPEC)
                type = LXC_AUTO_CGROUP_MIXED;
        else if (type == LXC_AUTO_CGROUP_FULL_NOSPEC)
                type = LXC_AUTO_CGROUP_FULL_MIXED;

        /* Mount tmpfs */
        tmpfspath = must_make_path(root, "/sys/fs/cgroup", NULL);
        ret = safe_mount(NULL, tmpfspath, "tmpfs",
                         MS_NOSUID | MS_NODEV | MS_NOEXEC | MS_RELATIME,
                         "size=10240k,mode=755", root);
        if (ret < 0)
                goto on_error;

        for (i = 0; ops->hierarchies[i]; i++) {
                char *controllerpath, *path2;
                struct hierarchy *h = ops->hierarchies[i];
                char *controller = strrchr(h->mountpoint, '/');

                if (!controller)
                        continue;
                controller++;

                controllerpath = must_make_path(tmpfspath, controller, NULL);
                if (dir_exists(controllerpath)) {
                        free(controllerpath);
                        continue;
                }

                ret = mkdir(controllerpath, 0755);
                if (ret < 0) {
                        SYSERROR("Error creating cgroup path: %s", controllerpath);
                        free(controllerpath);
                        goto on_error;
                }

                if (has_cgns && wants_force_mount) {
                        /* If cgroup namespaces are supported but the container
                         * will not have CAP_SYS_ADMIN after it has started we
                         * need to mount the cgroups manually.
                         */
                        ret = cg_mount_in_cgroup_namespace(type, h, controllerpath);
                        free(controllerpath);
                        if (ret < 0)
                                goto on_error;

                        continue;
                }

                ret = cg_mount_cgroup_full(type, h, controllerpath);
                if (ret < 0) {
                        free(controllerpath);
                        goto on_error;
                }

                if (!cg_mount_needs_subdirs(type)) {
                        free(controllerpath);
                        continue;
                }

                path2 = must_make_path(controllerpath, h->container_base_path,
                                       ops->container_cgroup, NULL);
                ret = mkdir_p(path2, 0755);
                if (ret < 0) {
                        free(controllerpath);
                        free(path2);
                        goto on_error;
                }

                ret = cg_legacy_mount_controllers(type, h, controllerpath,
                                                  path2, ops->container_cgroup);
                free(controllerpath);
                free(path2);
                if (ret < 0)
                        goto on_error;
        }
        retval = true;

on_error:
        free(tmpfspath);
        return retval;
}

static int recursive_count_nrtasks(char *dirname)
{
        struct dirent *direntp;
        DIR *dir;
        int count = 0, ret;
        char *path;

        dir = opendir(dirname);
        if (!dir)
                return 0;

        while ((direntp = readdir(dir))) {
                struct stat mystat;

                if (!strcmp(direntp->d_name, ".") ||
                    !strcmp(direntp->d_name, ".."))
                        continue;

                path = must_make_path(dirname, direntp->d_name, NULL);

                if (lstat(path, &mystat))
                        goto next;

                if (!S_ISDIR(mystat.st_mode))
                        goto next;

                count += recursive_count_nrtasks(path);
        next:
                free(path);
        }

        path = must_make_path(dirname, "cgroup.procs", NULL);
        ret = lxc_count_file_lines(path);
        if (ret != -1)
                count += ret;
        free(path);

        (void)closedir(dir);

        return count;
}

__cgfsng_ops static int cgfsng_nrtasks(struct cgroup_ops *ops)
{
        int count;
        char *path;

        if (!ops->container_cgroup || !ops->hierarchies)
                return -1;

        path = must_make_path(ops->hierarchies[0]->container_full_path, NULL);
        count = recursive_count_nrtasks(path);
        free(path);
        return count;
}

/* Only root needs to escape to the cgroup of its init. */
__cgfsng_ops static bool cgfsng_escape(const struct cgroup_ops *ops,
                                         struct lxc_conf *conf)
{
        int i;

        if (conf->cgroup_meta.relative || geteuid())
                return true;

        for (i = 0; ops->hierarchies[i]; i++) {
                int ret;
                char *fullpath;

                fullpath = must_make_path(ops->hierarchies[i]->mountpoint,
                                          ops->hierarchies[i]->container_base_path,
                                          "cgroup.procs", NULL);
                ret = lxc_write_to_file(fullpath, "0", 2, false, 0666);
                if (ret != 0) {
                        SYSERROR("Failed to escape to cgroup \"%s\"", fullpath);
                        free(fullpath);
                        return false;
                }
                free(fullpath);
        }

        return true;
}

__cgfsng_ops static int cgfsng_num_hierarchies(struct cgroup_ops *ops)
{
        int i;

        for (i = 0; ops->hierarchies[i]; i++)
                ;

        return i;
}

__cgfsng_ops static bool cgfsng_get_hierarchies(struct cgroup_ops *ops, int n, char ***out)
{
        int i;

        /* sanity check n */
        for (i = 0; i < n; i++)
                if (!ops->hierarchies[i])
                        return false;

        *out = ops->hierarchies[i]->controllers;

        return true;
}

#define THAWED "THAWED"
#define THAWED_LEN (strlen(THAWED))

/* TODO: If the unified cgroup hierarchy grows a freezer controller this needs
 * to be adapted.
 */
__cgfsng_ops static bool cgfsng_unfreeze(struct cgroup_ops *ops)
{
        int ret;
        char *fullpath;
        struct hierarchy *h;

        h = get_hierarchy(ops, "freezer");
        if (!h)
                return false;

        fullpath = must_make_path(h->container_full_path, "freezer.state", NULL);
        ret = lxc_write_to_file(fullpath, THAWED, THAWED_LEN, false, 0666);
        free(fullpath);
        if (ret < 0)
                return false;

        return true;
}

__cgfsng_ops static const char *cgfsng_get_cgroup(struct cgroup_ops *ops,
                                                    const char *controller)
{
        struct hierarchy *h;

        h = get_hierarchy(ops, controller);
        if (!h) {
                WARN("Failed to find hierarchy for controller \"%s\"",
                     controller ? controller : "(null)");
                return NULL;
        }

        return h->container_full_path ? h->container_full_path + strlen(h->mountpoint) : NULL;
}

/* Given a cgroup path returned from lxc_cmd_get_cgroup_path, build a full path,
 * which must be freed by the caller.
 */
static inline char *build_full_cgpath_from_monitorpath(struct hierarchy *h,
                                                       const char *inpath,
                                                       const char *filename)
{
        return must_make_path(h->mountpoint, inpath, filename, NULL);
}

/* Technically, we're always at a delegation boundary here (This is especially
 * true when cgroup namespaces are available.). The reasoning is that in order
 * for us to have been able to start a container in the first place the root
 * cgroup must have been a leaf node. Now, either the container's init system
 * has populated the cgroup and kept it as a leaf node or it has created
 * subtrees. In the former case we will simply attach to the leaf node we
 * created when we started the container in the latter case we create our own
 * cgroup for the attaching process.
 */
static int __cg_unified_attach(const struct hierarchy *h, const char *name,
                               const char *lxcpath, const char *pidstr,
                               size_t pidstr_len, const char *controller)
{
        int ret;
        size_t len;
        int fret = -1, idx = 0;
        char *base_path = NULL, *container_cgroup = NULL, *full_path = NULL;

        container_cgroup = lxc_cmd_get_cgroup_path(name, lxcpath, controller);
        /* not running */
        if (!container_cgroup)
                return 0;

        base_path = must_make_path(h->mountpoint, container_cgroup, NULL);
        full_path = must_make_path(base_path, "cgroup.procs", NULL);
        /* cgroup is populated */
        ret = lxc_write_to_file(full_path, pidstr, pidstr_len, false, 0666);
        if (ret < 0 && errno != EBUSY)
                goto on_error;

        if (ret == 0)
                goto on_success;

        free(full_path);

        len = strlen(base_path) + STRLITERALLEN("/lxc-1000") +
              STRLITERALLEN("/cgroup-procs");
        full_path = must_alloc(len + 1);
        do {
                if (idx)
                        ret = snprintf(full_path, len + 1, "%s/lxc-%d",
                                       base_path, idx);
                else
                        ret = snprintf(full_path, len + 1, "%s/lxc", base_path);
                if (ret < 0 || (size_t)ret >= len + 1)
                        goto on_error;

                ret = mkdir_p(full_path, 0755);
                if (ret < 0 && errno != EEXIST)
                        goto on_error;

                (void)strlcat(full_path, "/cgroup.procs", len + 1);
                ret = lxc_write_to_file(full_path, pidstr, len, false, 0666);
                if (ret == 0)
                        goto on_success;

                /* this is a non-leaf node */
                if (errno != EBUSY)
                        goto on_error;

        } while (++idx > 0 && idx < 1000);

on_success:
        if (idx < 1000)
                fret = 0;

on_error:
        free(base_path);
        free(container_cgroup);
        free(full_path);

        return fret;
}

__cgfsng_ops static bool cgfsng_attach(struct cgroup_ops *ops, const char *name,
                                         const char *lxcpath, pid_t pid)
{
        int i, len, ret;
        char pidstr[INTTYPE_TO_STRLEN(pid_t)];

        len = snprintf(pidstr, sizeof(pidstr), "%d", pid);
        if (len < 0 || (size_t)len >= sizeof(pidstr))
                return false;

        for (i = 0; ops->hierarchies[i]; i++) {
                char *path;
                char *fullpath = NULL;
                struct hierarchy *h = ops->hierarchies[i];

                if (h->version == CGROUP2_SUPER_MAGIC) {
                        ret = __cg_unified_attach(h, name, lxcpath, pidstr, len,
                                                  h->controllers[0]);
                        if (ret < 0)
                                return false;

                        continue;
                }

                path = lxc_cmd_get_cgroup_path(name, lxcpath, h->controllers[0]);
                /* not running */
                if (!path)
                        continue;

                fullpath = build_full_cgpath_from_monitorpath(h, path, "cgroup.procs");
                free(path);
                ret = lxc_write_to_file(fullpath, pidstr, len, false, 0666);
                if (ret < 0) {
                        SYSERROR("Failed to attach %d to %s", (int)pid, fullpath);
                        free(fullpath);
                        return false;
                }
                free(fullpath);
        }

        return true;
}

/* Called externally (i.e. from 'lxc-cgroup') to query cgroup limits.  Here we
 * don't have a cgroup_data set up, so we ask the running container through the
 * commands API for the cgroup path.
 */
__cgfsng_ops static int cgfsng_get(struct cgroup_ops *ops, const char *filename,
                                     char *value, size_t len, const char *name,
                                     const char *lxcpath)
{
        int ret = -1;
        size_t controller_len;
        char *controller, *p, *path;
        struct hierarchy *h;

        controller_len = strlen(filename);
        controller = alloca(controller_len + 1);
        (void)strlcpy(controller, filename, controller_len + 1);

        p = strchr(controller, '.');
        if (p)
                *p = '\0';

        path = lxc_cmd_get_cgroup_path(name, lxcpath, controller);
        /* not running */
        if (!path)
                return -1;

        h = get_hierarchy(ops, controller);
        if (h) {
                char *fullpath;

                fullpath = build_full_cgpath_from_monitorpath(h, path, filename);
                ret = lxc_read_from_file(fullpath, value, len);
                free(fullpath);
        }
        free(path);

        return ret;
}

/* Called externally (i.e. from 'lxc-cgroup') to set new cgroup limits.  Here we
 * don't have a cgroup_data set up, so we ask the running container through the
 * commands API for the cgroup path.
 */
__cgfsng_ops static int cgfsng_set(struct cgroup_ops *ops,
                                     const char *filename, const char *value,
                                     const char *name, const char *lxcpath)
{
        int ret = -1;
        size_t controller_len;
        char *controller, *p, *path;
        struct hierarchy *h;

        controller_len = strlen(filename);
        controller = alloca(controller_len + 1);
        (void)strlcpy(controller, filename, controller_len + 1);

        p = strchr(controller, '.');
        if (p)
                *p = '\0';

        path = lxc_cmd_get_cgroup_path(name, lxcpath, controller);
        /* not running */
        if (!path)
                return -1;

        h = get_hierarchy(ops, controller);
        if (h) {
                char *fullpath;

                fullpath = build_full_cgpath_from_monitorpath(h, path, filename);
                ret = lxc_write_to_file(fullpath, value, strlen(value), false, 0666);
                free(fullpath);
        }
        free(path);

        return ret;
}

/* take devices cgroup line
 *    /dev/foo rwx
 * and convert it to a valid
 *    type major:minor mode
 * line. Return <0 on error. Dest is a preallocated buffer long enough to hold
 * the output.
 */
static int convert_devpath(const char *invalue, char *dest)
{
        int n_parts;
        char *p, *path, type;
        unsigned long minor, major;
        struct stat sb;
        int ret = -EINVAL;
        char *mode = NULL;

        path = must_copy_string(invalue);

        /* Read path followed by mode. Ignore any trailing text.
         * A '    # comment' would be legal. Technically other text is not
         * legal, we could check for that if we cared to.
         */
        for (n_parts = 1, p = path; *p && n_parts < 3; p++) {
                if (*p != ' ')
                        continue;
                *p = '\0';

                if (n_parts != 1)
                        break;
                p++;
                n_parts++;

                while (*p == ' ')
                        p++;

                mode = p;

                if (*p == '\0')
                        goto out;
        }

        if (n_parts == 1)
                goto out;

        ret = stat(path, &sb);
        if (ret < 0)
                goto out;

        mode_t m = sb.st_mode & S_IFMT;
        switch (m) {
        case S_IFBLK:
                type = 'b';
                break;
        case S_IFCHR:
                type = 'c';
                break;
        default:
                ERROR("Unsupported device type %i for \"%s\"", m, path);
                ret = -EINVAL;
                goto out;
        }

        major = MAJOR(sb.st_rdev);
        minor = MINOR(sb.st_rdev);
        ret = snprintf(dest, 50, "%c %lu:%lu %s", type, major, minor, mode);
        if (ret < 0 || ret >= 50) {
                ERROR("Error on configuration value \"%c %lu:%lu %s\" (max 50 "
                      "chars)", type, major, minor, mode);
                ret = -ENAMETOOLONG;
                goto out;
        }
        ret = 0;

out:
        free(path);
        return ret;
}

/* Called from setup_limits - here we have the container's cgroup_data because
 * we created the cgroups.
 */
static int cg_legacy_set_data(struct cgroup_ops *ops, const char *filename,
                              const char *value)
{
        size_t len;
        char *fullpath, *p;
        /* "b|c <2^64-1>:<2^64-1> r|w|m" = 47 chars max */
        char converted_value[50];
        struct hierarchy *h;
        int ret = 0;
        char *controller = NULL;

        len = strlen(filename);
        controller = alloca(len + 1);
        (void)strlcpy(controller, filename, len + 1);

        p = strchr(controller, '.');
        if (p)
                *p = '\0';

        if (strcmp("devices.allow", filename) == 0 && value[0] == '/') {
                ret = convert_devpath(value, converted_value);
                if (ret < 0)
                        return ret;
                value = converted_value;
        }

        h = get_hierarchy(ops, controller);
        if (!h) {
                ERROR("Failed to setup limits for the \"%s\" controller. "
                      "The controller seems to be unused by \"cgfsng\" cgroup "
                      "driver or not enabled on the cgroup hierarchy",
                      controller);
                errno = ENOENT;
                return -ENOENT;
        }

        fullpath = must_make_path(h->container_full_path, filename, NULL);
        ret = lxc_write_to_file(fullpath, value, strlen(value), false, 0666);
        free(fullpath);
        return ret;
}

static bool __cg_legacy_setup_limits(struct cgroup_ops *ops,
                                     struct lxc_list *cgroup_settings,
                                     bool do_devices)
{
        struct lxc_list *iterator, *next, *sorted_cgroup_settings;
        struct lxc_cgroup *cg;
        bool ret = false;

        if (lxc_list_empty(cgroup_settings))
                return true;

        sorted_cgroup_settings = sort_cgroup_settings(cgroup_settings);
        if (!sorted_cgroup_settings)
                return false;

        lxc_list_for_each(iterator, sorted_cgroup_settings) {
                cg = iterator->elem;

                if (do_devices == !strncmp("devices", cg->subsystem, 7)) {
                        if (cg_legacy_set_data(ops, cg->subsystem, cg->value)) {
                                if (do_devices && (errno == EACCES || errno == EPERM)) {
                                        WARN("Failed to set \"%s\" to \"%s\"",
                                             cg->subsystem, cg->value);
                                        continue;
                                }
                                WARN("Failed to set \"%s\" to \"%s\"",
                                     cg->subsystem, cg->value);
                                goto out;
                        }
                        DEBUG("Set controller \"%s\" set to \"%s\"",
                              cg->subsystem, cg->value);
                }
        }

        ret = true;
        INFO("Limits for the legacy cgroup hierarchies have been setup");
out:
        lxc_list_for_each_safe(iterator, sorted_cgroup_settings, next) {
                lxc_list_del(iterator);
                free(iterator);
        }
        free(sorted_cgroup_settings);
        return ret;
}

static bool __cg_unified_setup_limits(struct cgroup_ops *ops,
                                      struct lxc_list *cgroup_settings)
{
        struct lxc_list *iterator;
        struct hierarchy *h = ops->unified;

        if (lxc_list_empty(cgroup_settings))
                return true;

        if (!h)
                return false;

        lxc_list_for_each(iterator, cgroup_settings) {
                int ret;
                char *fullpath;
                struct lxc_cgroup *cg = iterator->elem;

                fullpath = must_make_path(h->container_full_path, cg->subsystem, NULL);
                ret = lxc_write_to_file(fullpath, cg->value, strlen(cg->value), false, 0666);
                free(fullpath);
                if (ret < 0) {
                        SYSERROR("Failed to set \"%s\" to \"%s\"",
                                 cg->subsystem, cg->value);
                        return false;
                }
                TRACE("Set \"%s\" to \"%s\"", cg->subsystem, cg->value);
        }

        INFO("Limits for the unified cgroup hierarchy have been setup");
        return true;
}

__cgfsng_ops static bool cgfsng_setup_limits(struct cgroup_ops *ops,
                                               struct lxc_conf *conf,
                                               bool do_devices)
{
        bool bret;

        bret = __cg_legacy_setup_limits(ops, &conf->cgroup, do_devices);
        if (!bret)
                return false;

        return __cg_unified_setup_limits(ops, &conf->cgroup2);
}

static bool cgroup_use_wants_controllers(const struct cgroup_ops *ops,
                                       char **controllers)
{
        char **cur_ctrl, **cur_use;

        if (!ops->cgroup_use)
                return true;

        for (cur_ctrl = controllers; cur_ctrl && *cur_ctrl; cur_ctrl++) {
                bool found = false;

                for (cur_use = ops->cgroup_use; cur_use && *cur_use; cur_use++) {
                        if (strcmp(*cur_use, *cur_ctrl) != 0)
                                continue;

                        found = true;
                        break;
                }

                if (found)
                        continue;

                return false;
        }

        return true;
}

/* At startup, parse_hierarchies finds all the info we need about cgroup
 * mountpoints and current cgroups, and stores it in @d.
 */
static bool cg_hybrid_init(struct cgroup_ops *ops, bool relative)
{
        int ret;
        char *basecginfo;
        FILE *f;
        size_t len = 0;
        char *line = NULL;
        char **klist = NULL, **nlist = NULL;

        /* Root spawned containers escape the current cgroup, so use init's
         * cgroups as our base in that case.
         */
        if (!relative && (geteuid() == 0))
                basecginfo = read_file("/proc/1/cgroup");
        else
                basecginfo = read_file("/proc/self/cgroup");
        if (!basecginfo)
                return false;

        ret = get_existing_subsystems(&klist, &nlist);
        if (ret < 0) {
                ERROR("Failed to retrieve available legacy cgroup controllers");
                free(basecginfo);
                return false;
        }

        f = fopen("/proc/self/mountinfo", "r");
        if (!f) {
                ERROR("Failed to open \"/proc/self/mountinfo\"");
                free(basecginfo);
                return false;
        }

        lxc_cgfsng_print_basecg_debuginfo(basecginfo, klist, nlist);

        while (getline(&line, &len, f) != -1) {
                int type;
                bool writeable;
                struct hierarchy *new;
                char *base_cgroup = NULL, *mountpoint = NULL;
                char **controller_list = NULL;

                type = get_cgroup_version(line);
                if (type == 0)
                        continue;

                if (type == CGROUP2_SUPER_MAGIC && ops->unified)
                        continue;

                if (ops->cgroup_layout == CGROUP_LAYOUT_UNKNOWN) {
                        if (type == CGROUP2_SUPER_MAGIC)
                                ops->cgroup_layout = CGROUP_LAYOUT_UNIFIED;
                        else if (type == CGROUP_SUPER_MAGIC)
                                ops->cgroup_layout = CGROUP_LAYOUT_LEGACY;
                } else if (ops->cgroup_layout == CGROUP_LAYOUT_UNIFIED) {
                        if (type == CGROUP_SUPER_MAGIC)
                                ops->cgroup_layout = CGROUP_LAYOUT_HYBRID;
                } else if (ops->cgroup_layout == CGROUP_LAYOUT_LEGACY) {
                        if (type == CGROUP2_SUPER_MAGIC)
                                ops->cgroup_layout = CGROUP_LAYOUT_HYBRID;
                }

                controller_list = cg_hybrid_get_controllers(klist, nlist, line, type);
                if (!controller_list && type == CGROUP_SUPER_MAGIC)
                        continue;

                if (type == CGROUP_SUPER_MAGIC)
                        if (controller_list_is_dup(ops->hierarchies, controller_list))
                                goto next;

                mountpoint = cg_hybrid_get_mountpoint(line);
                if (!mountpoint) {
                        ERROR("Failed parsing mountpoint from \"%s\"", line);
                        goto next;
                }

                if (type == CGROUP_SUPER_MAGIC)
                        base_cgroup = cg_hybrid_get_current_cgroup(basecginfo, controller_list[0], CGROUP_SUPER_MAGIC);
                else
                        base_cgroup = cg_hybrid_get_current_cgroup(basecginfo, NULL, CGROUP2_SUPER_MAGIC);
                if (!base_cgroup) {
                        ERROR("Failed to find current cgroup");
                        goto next;
                }

                trim(base_cgroup);
                prune_init_scope(base_cgroup);
                if (type == CGROUP2_SUPER_MAGIC)
                        writeable = test_writeable_v2(mountpoint, base_cgroup);
                else
                        writeable = test_writeable_v1(mountpoint, base_cgroup);
                if (!writeable)
                        goto next;

                if (type == CGROUP2_SUPER_MAGIC) {
                        char *cgv2_ctrl_path;

                        cgv2_ctrl_path = must_make_path(mountpoint, base_cgroup,
                                                        "cgroup.controllers",
                                                        NULL);

                        controller_list = cg_unified_get_controllers(cgv2_ctrl_path);
                        free(cgv2_ctrl_path);
                        if (!controller_list) {
                                controller_list = cg_unified_make_empty_controller();
                                TRACE("No controllers are enabled for "
                                      "delegation in the unified hierarchy");
                        }
                }

                /* Exclude all controllers that cgroup use does not want. */
                if (!cgroup_use_wants_controllers(ops, controller_list))
                        goto next;

                new = add_hierarchy(&ops->hierarchies, controller_list, mountpoint, base_cgroup, type);
                if (type == CGROUP2_SUPER_MAGIC && !ops->unified)
                        ops->unified = new;

                continue;

        next:
                free_string_list(controller_list);
                free(mountpoint);
                free(base_cgroup);
        }

        free_string_list(klist);
        free_string_list(nlist);

        free(basecginfo);

        fclose(f);
        free(line);

        TRACE("Writable cgroup hierarchies:");
        lxc_cgfsng_print_hierarchies(ops);

        /* verify that all controllers in cgroup.use and all crucial
         * controllers are accounted for
         */
        if (!all_controllers_found(ops))
                return false;

        return true;
}

static int cg_is_pure_unified(void)
{

        int ret;
        struct statfs fs;

        ret = statfs("/sys/fs/cgroup", &fs);
        if (ret < 0)
                return -ENOMEDIUM;

        if (is_fs_type(&fs, CGROUP2_SUPER_MAGIC))
                return CGROUP2_SUPER_MAGIC;

        return 0;
}

/* Get current cgroup from /proc/self/cgroup for the cgroupfs v2 hierarchy. */
static char *cg_unified_get_current_cgroup(bool relative)
{
        char *basecginfo, *base_cgroup;
        char *copy = NULL;

        if (!relative && (geteuid() == 0))
                basecginfo = read_file("/proc/1/cgroup");
        else
                basecginfo = read_file("/proc/self/cgroup");
        if (!basecginfo)
                return NULL;

        base_cgroup = strstr(basecginfo, "0::/");
        if (!base_cgroup)
                goto cleanup_on_err;

        base_cgroup = base_cgroup + 3;
        copy = copy_to_eol(base_cgroup);
        if (!copy)
                goto cleanup_on_err;

cleanup_on_err:
        free(basecginfo);
        if (copy)
                trim(copy);

        return copy;
}

static int cg_unified_init(struct cgroup_ops *ops, bool relative)
{
        int ret;
        char *mountpoint, *subtree_path;
        char **delegatable;
        char *base_cgroup = NULL;

        ret = cg_is_pure_unified();
        if (ret == -ENOMEDIUM)
                return -ENOMEDIUM;

        if (ret != CGROUP2_SUPER_MAGIC)
                return 0;

        base_cgroup = cg_unified_get_current_cgroup(relative);
        if (!base_cgroup)
                return -EINVAL;
        prune_init_scope(base_cgroup);

        /* We assume that we have already been given controllers to delegate
         * further down the hierarchy. If not it is up to the user to delegate
         * them to us.
         */
        mountpoint = must_copy_string("/sys/fs/cgroup");
        subtree_path = must_make_path(mountpoint, base_cgroup,
                                      "cgroup.subtree_control", NULL);
        delegatable = cg_unified_get_controllers(subtree_path);
        free(subtree_path);
        if (!delegatable)
                delegatable = cg_unified_make_empty_controller();
        if (!delegatable[0])
                TRACE("No controllers are enabled for delegation");

        /* TODO: If the user requested specific controllers via lxc.cgroup.use
         * we should verify here. The reason I'm not doing it right is that I'm
         * not convinced that lxc.cgroup.use will be the future since it is a
         * global property. I much rather have an option that lets you request
         * controllers per container.
         */

        add_hierarchy(&ops->hierarchies, delegatable, mountpoint, base_cgroup, CGROUP2_SUPER_MAGIC);

        ops->cgroup_layout = CGROUP_LAYOUT_UNIFIED;
        return CGROUP2_SUPER_MAGIC;
}

static bool cg_init(struct cgroup_ops *ops, struct lxc_conf *conf)
{
        int ret;
        const char *tmp;
        bool relative = conf->cgroup_meta.relative;

        tmp = lxc_global_config_value("lxc.cgroup.use");
        if (tmp) {
                char *chop, *cur, *pin;

                pin = must_copy_string(tmp);
                chop = pin;

                lxc_iterate_parts(cur, chop, ",") {
                        must_append_string(&ops->cgroup_use, cur);
                }

                free(pin);
        }

        ret = cg_unified_init(ops, relative);
        if (ret < 0)
                return false;

        if (ret == CGROUP2_SUPER_MAGIC)
                return true;

        return cg_hybrid_init(ops, relative);
}

__cgfsng_ops static bool cgfsng_data_init(struct cgroup_ops *ops)
{
        const char *cgroup_pattern;

        /* copy system-wide cgroup information */
        cgroup_pattern = lxc_global_config_value("lxc.cgroup.pattern");
        if (!cgroup_pattern) {
                /* lxc.cgroup.pattern is only NULL on error. */
                ERROR("Failed to retrieve cgroup pattern");
                return false;
        }
        ops->cgroup_pattern = must_copy_string(cgroup_pattern);
        ops->monitor_pattern = MONITOR_CGROUP;

        return true;
}

struct cgroup_ops *cgfsng_ops_init(struct lxc_conf *conf)
{
        struct cgroup_ops *cgfsng_ops;

        cgfsng_ops = malloc(sizeof(struct cgroup_ops));
        if (!cgfsng_ops)
                return NULL;

        memset(cgfsng_ops, 0, sizeof(struct cgroup_ops));
        cgfsng_ops->cgroup_layout = CGROUP_LAYOUT_UNKNOWN;

        if (!cg_init(cgfsng_ops, conf)) {
                free(cgfsng_ops);
                return NULL;
        }

        cgfsng_ops->data_init = cgfsng_data_init;
        cgfsng_ops->payload_destroy = cgfsng_payload_destroy;
        cgfsng_ops->monitor_destroy = cgfsng_monitor_destroy;
        cgfsng_ops->monitor_create = cgfsng_monitor_create;
        cgfsng_ops->monitor_enter = cgfsng_monitor_enter;
        cgfsng_ops->payload_create = cgfsng_payload_create;
        cgfsng_ops->payload_enter = cgfsng_payload_enter;
        cgfsng_ops->escape = cgfsng_escape;
        cgfsng_ops->num_hierarchies = cgfsng_num_hierarchies;
        cgfsng_ops->get_hierarchies = cgfsng_get_hierarchies;
        cgfsng_ops->get_cgroup = cgfsng_get_cgroup;
        cgfsng_ops->get = cgfsng_get;
        cgfsng_ops->set = cgfsng_set;
        cgfsng_ops->unfreeze = cgfsng_unfreeze;
        cgfsng_ops->setup_limits = cgfsng_setup_limits;
        cgfsng_ops->driver = "cgfsng";
        cgfsng_ops->version = "1.0.0";
        cgfsng_ops->attach = cgfsng_attach;
        cgfsng_ops->chown = cgfsng_chown;
        cgfsng_ops->mount = cgfsng_mount;
        cgfsng_ops->nrtasks = cgfsng_nrtasks;

        return cgfsng_ops;
}