libfstools/mount.c

   1 /*
   2  * Copyright (C) 2014 John Crispin <blogic@openwrt.org>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU Lesser General Public License version 2.1
   6  * as published by the Free Software Foundation
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  * GNU General Public License for more details.
  12  */
  13
  14 #include <sys/types.h>
  15 #include <sys/stat.h>
  16 #include <sys/mount.h>
  17
  18 #include <errno.h>
  19 #include <stdio.h>
  20 #include <unistd.h>
  21 #include <string.h>
  22
  23 #include "libfstools.h"
  24
  25 /* this is a raw syscall - man 2 pivot_root */
  26 extern int pivot_root(const char *new_root, const char *put_old);
  27
  28 /**
  29  * mount_move - move mounted point to the new location
  30  *
  31  * @oldroot: directory that is current location of mount point
  32  * @newroot: new directory for the mount point
  33  */
  34 int
  35 mount_move(const char *oldroot, const char *newroot, const char *dir)
  36 {
  37 #ifndef MS_MOVE
  38 #define MS_MOVE (1 << 13)
  39 #endif
  40         struct stat s;
  41         char olddir[64];
  42         char newdir[64];
  43         int ret;
  44
  45         snprintf(olddir, sizeof(olddir), "%s%s", oldroot, dir);
  46         snprintf(newdir, sizeof(newdir), "%s%s", newroot, dir);
  47
  48         if (stat(olddir, &s) || !S_ISDIR(s.st_mode))
  49                 return -1;
  50
  51         if (stat(newdir, &s) || !S_ISDIR(s.st_mode))
  52                 return -1;
  53
  54         ret = mount(olddir, newdir, NULL, MS_NOATIME | MS_MOVE, NULL);
  55
  56 /*      if (ret)
  57                 ULOG_ERR("failed %s %s: %s\n", olddir, newdir, strerror(errno));*/
  58
  59         return ret;
  60 }
  61
  62 int
  63 pivot(char *new, char *old)
  64 {
  65         char pivotdir[64];
  66         int ret;
  67
  68         if (mount_move("", new, "/proc"))
  69                 return -1;
  70
  71         snprintf(pivotdir, sizeof(pivotdir), "%s%s", new, old);
  72
  73         ret = pivot_root(new, pivotdir);
  74
  75         if (ret < 0) {
  76                 ULOG_ERR("pivot_root failed %s %s: %s\n", new, pivotdir, strerror(errno));
  77                 return -1;
  78         }
  79
  80         mount_move(old, "", "/dev");
  81         mount_move(old, "", "/tmp");
  82         mount_move(old, "", "/sys");
  83         mount_move(old, "", "/overlay");
  84
  85         return 0;
  86 }
  87
  88 /**
  89  * fopivot - switch to overlay using passed dir as upper one
  90  *
  91  * @rw_root: writable directory that will be used as upper dir
  92  * @ro_root: directory where old root will be put
  93  */
  94 int
  95 fopivot(char *rw_root, char *ro_root)
  96 {
  97         char overlay[64], mount_options[64];
  98
  99         if (find_filesystem("overlay")) {
 100                 ULOG_ERR("BUG: no suitable fs found\n");
 101                 return -1;
 102         }
 103
 104         snprintf(overlay, sizeof(overlay), "overlayfs:%s", rw_root);
 105
 106         /*
 107          * First, try to mount without a workdir, for overlayfs v22 and before.
 108          * If it fails, it means that we are probably using a v23 and
 109          * later versions that require a workdir
 110          */
 111         snprintf(mount_options, sizeof(mount_options), "lowerdir=/,upperdir=%s", rw_root);
 112         if (mount(overlay, "/mnt", "overlayfs", MS_NOATIME, mount_options)) {
 113                 char upperdir[64], workdir[64], upgrade[64], upgrade_dest[64];
 114                 struct stat st;
 115
 116                 snprintf(upperdir, sizeof(upperdir), "%s/upper", rw_root);
 117                 snprintf(workdir, sizeof(workdir), "%s/work", rw_root);
 118                 snprintf(upgrade, sizeof(upgrade), "%s/sysupgrade.tgz", rw_root);
 119                 snprintf(upgrade_dest, sizeof(upgrade_dest), "%s/sysupgrade.tgz", upperdir);
 120                 snprintf(mount_options, sizeof(mount_options), "lowerdir=/,upperdir=%s,workdir=%s",
 121                          upperdir, workdir);
 122
 123                 /*
 124                  * Overlay FS v23 and later requires both a upper and
 125                  * a work directory, both on the same filesystem, but
 126                  * not part of the same subtree.
 127                  * We can't really deal with these constraints without
 128                  * creating two new subdirectories in /overlay.
 129                  */
 130                 mkdir(upperdir, 0755);
 131                 mkdir(workdir, 0755);
 132
 133                 if (stat(upgrade, &st) == 0)
 134                     rename(upgrade, upgrade_dest);
 135
 136                 /* Mainlined overlayfs has been renamed to "overlay", try that first */
 137                 if (mount(overlay, "/mnt", "overlay", MS_NOATIME, mount_options)) {
 138                         if (mount(overlay, "/mnt", "overlayfs", MS_NOATIME, mount_options)) {
 139                                 ULOG_ERR("mount failed: %s, options %s\n",
 140                                          strerror(errno), mount_options);
 141                                 return -1;
 142                         }
 143                 }
 144         }
 145
 146         return pivot("/mnt", ro_root);
 147 }
 148
 149 /**
 150  * ramoverlay - use RAM to store filesystem changes on top of RO root
 151  */
 152 int
 153 ramoverlay(void)
 154 {
 155         mkdir("/tmp/root", 0755);
 156         mount("tmpfs", "/tmp/root", "tmpfs", MS_NOATIME, "mode=0755");
 157
 158         return fopivot("/tmp/root", "/rom");
 159 }