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 #include <sys/wait.h>
  18
  19 #include <errno.h>
  20 #include <stdio.h>
  21 #include <unistd.h>
  22 #include <string.h>
  23
  24 #include "libfstools.h"
  25
  26 /* this is a raw syscall - man 2 pivot_root */
  27 extern int pivot_root(const char *new_root, const char *put_old);
  28
  29 /**
  30  * mount_move - move mounted point to the new location
  31  *
  32  * @oldroot: directory that is current location of mount point
  33  * @newroot: new directory for the mount point
  34  */
  35 int
  36 mount_move(const char *oldroot, const char *newroot, const char *dir)
  37 {
  38 #ifndef MS_MOVE
  39 #define MS_MOVE (1 << 13)
  40 #endif
  41         struct stat s;
  42         char olddir[64];
  43         char newdir[64];
  44         int ret;
  45
  46         snprintf(olddir, sizeof(olddir), "%s%s", oldroot, dir);
  47         snprintf(newdir, sizeof(newdir), "%s%s", newroot, dir);
  48
  49         if (stat(olddir, &s) || !S_ISDIR(s.st_mode))
  50                 return -1;
  51
  52         if (stat(newdir, &s) || !S_ISDIR(s.st_mode))
  53                 return -1;
  54
  55         ret = mount(olddir, newdir, NULL, MS_NOATIME | MS_MOVE, NULL);
  56
  57 /*      if (ret)
  58                 ULOG_ERR("failed %s %s: %m\n", olddir, newdir);*/
  59
  60         return ret;
  61 }
  62
  63 int
  64 pivot(char *new, char *old)
  65 {
  66         char pivotdir[64];
  67         int ret;
  68
  69         if (mount_move("", new, "/proc"))
  70                 return -1;
  71
  72         snprintf(pivotdir, sizeof(pivotdir), "%s%s", new, old);
  73
  74         ret = pivot_root(new, pivotdir);
  75
  76         if (ret < 0) {
  77                 ULOG_ERR("pivot_root failed %s %s: %m\n", new, pivotdir);
  78                 return -1;
  79         }
  80
  81         mount_move(old, "", "/dev");
  82         mount_move(old, "", "/tmp");
  83         mount_move(old, "", "/sys");
  84         mount_move(old, "", "/overlay");
  85
  86         return 0;
  87 }
  88
  89 /**
  90  * fopivot - switch to overlay using passed dir as upper one
  91  *
  92  * @rw_root: writable directory that will be used as upper dir
  93  * @ro_root: directory where old root will be put
  94  */
  95 int
  96 fopivot(char *rw_root, char *ro_root)
  97 {
  98         char overlay[64], mount_options[64], upperdir[64], workdir[64], upgrade[64], upgrade_dest[64];
  99         struct stat st;
 100
 101         if (find_filesystem("overlay")) {
 102                 ULOG_ERR("BUG: no suitable fs found\n");
 103                 return -1;
 104         }
 105
 106         snprintf(overlay, sizeof(overlay), "overlayfs:%s", rw_root);
 107         snprintf(upperdir, sizeof(upperdir), "%s/upper", rw_root);
 108         snprintf(workdir, sizeof(workdir), "%s/work", rw_root);
 109         snprintf(upgrade, sizeof(upgrade), "%s/sysupgrade.tgz", rw_root);
 110         snprintf(upgrade_dest, sizeof(upgrade_dest), "%s/sysupgrade.tgz", upperdir);
 111         snprintf(mount_options, sizeof(mount_options), "lowerdir=/,upperdir=%s,workdir=%s",
 112                  upperdir, workdir);
 113
 114         /*
 115          * Overlay FS v23 and later requires both a upper and
 116          * a work directory, both on the same filesystem, but
 117          * not part of the same subtree.
 118          * We can't really deal with these constraints without
 119          * creating two new subdirectories in /overlay.
 120          */
 121         if (mkdir(upperdir, 0755) == -1 && errno != EEXIST)
 122                 return -1;
 123
 124         if (mkdir(workdir, 0755) == -1 && errno != EEXIST)
 125                 return -1;
 126
 127         if (stat(upgrade, &st) == 0)
 128                 rename(upgrade, upgrade_dest);
 129
 130         if (mount(overlay, "/mnt", "overlay", MS_NOATIME, mount_options)) {
 131                 ULOG_ERR("mount failed: %m, options %s\n", mount_options);
 132                 return -1;
 133         }
 134
 135         return pivot("/mnt", ro_root);
 136 }
 137
 138 /**
 139  * ramoverlay - use RAM to store filesystem changes on top of RO root
 140  */
 141 int
 142 ramoverlay(void)
 143 {
 144         mkdir("/tmp/root", 0755);
 145         mount("tmpfs", "/tmp/root", "tmpfs", MS_NOATIME, "mode=0755");
 146
 147         return fopivot("/tmp/root", "/rom");
 148 }