src/lxc/cgroups/cgroup_utils.c

   1 /*
   2  * lxc: linux Container library
   3  *
   4  * Copyright © 2017 Canonical Ltd.
   5  *
   6  * Authors:
   7  * Serge Hallyn <serge.hallyn@ubuntu.com>
   8  * Christian Brauner <christian.brauner@ubuntu.com>
   9  *
  10  * This library is free software; you can redistribute it and/or
  11  * modify it under the terms of the GNU Lesser General Public
  12  * License as published by the Free Software Foundation; either
  13  * version 2.1 of the License, or (at your option) any later version.
  14  *
  15  * This library is distributed in the hope that it will be useful,
  16  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  17  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  18  * Lesser General Public License for more details.
  19  *
  20  * You should have received a copy of the GNU Lesser General Public
  21  * License along with this library; if not, write to the Free Software
  22  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  23  */
  24
  25 #ifndef _GNU_SOURCE
  26 #define _GNU_SOURCE 1
  27 #endif
  28 #include <stdbool.h>
  29 #include <stdlib.h>
  30 #include <string.h>
  31 #include <unistd.h>
  32
  33 #include "cgroup_utils.h"
  34 #include "config.h"
  35 #include "macro.h"
  36 #include "memory_utils.h"
  37 #include "utils.h"
  38
  39 int get_cgroup_version(char *line)
  40 {
  41         if (is_cgroupfs_v1(line))
  42                 return CGROUP_SUPER_MAGIC;
  43
  44         if (is_cgroupfs_v2(line))
  45                 return CGROUP2_SUPER_MAGIC;
  46
  47         return 0;
  48 }
  49
  50 bool is_cgroupfs_v1(char *line)
  51 {
  52         char *p = strstr(line, " - ");
  53         if (!p)
  54                 return false;
  55         return strncmp(p, " - cgroup ", 10) == 0;
  56 }
  57
  58 bool is_cgroupfs_v2(char *line)
  59 {
  60         char *p = strstr(line, " - ");
  61         if (!p)
  62                 return false;
  63
  64         return strncmp(p, " - cgroup2 ", 11) == 0;
  65 }
  66
  67 bool test_writeable_v1(char *mountpoint, char *path)
  68 {
  69         __do_free char *fullpath = must_make_path(mountpoint, path, NULL);
  70         return (access(fullpath, W_OK) == 0);
  71 }
  72
  73 bool test_writeable_v2(char *mountpoint, char *path)
  74 {
  75         /* In order to move ourselves into an appropriate sub-cgroup we need to
  76          * have write access to the parent cgroup's "cgroup.procs" file, i.e. we
  77          * need to have write access to the our current cgroups's "cgroup.procs"
  78          * file.
  79          */
  80         int ret;
  81         __do_free char *cgroup_path = NULL, *cgroup_procs_file = NULL,
  82                        *cgroup_threads_file = NULL;
  83
  84         cgroup_path = must_make_path(mountpoint, path, NULL);
  85         cgroup_procs_file = must_make_path(cgroup_path, "cgroup.procs", NULL);
  86
  87         ret = access(cgroup_path, W_OK);
  88         if (ret < 0)
  89                 return false;
  90
  91         ret = access(cgroup_procs_file, W_OK);
  92         if (ret < 0)
  93                 return false;
  94
  95         /* Newer versions of cgroup2 now also require write access to the
  96          * "cgroup.threads" file.
  97          */
  98         cgroup_threads_file = must_make_path(cgroup_path, "cgroup.threads", NULL);
  99         if (!file_exists(cgroup_threads_file))
 100                 return true;
 101
 102         return (access(cgroup_threads_file, W_OK) == 0);
 103 }