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 int
  29 mount_move(char *oldroot, char *newroot, char *dir)
  30 {
  31 #ifndef MS_MOVE
  32 #define MS_MOVE (1 << 13)
  33 #endif
  34         struct stat s;
  35         char olddir[64];
  36         char newdir[64];
  37         int ret;
  38
  39         snprintf(olddir, sizeof(olddir), "%s%s", oldroot, dir);
  40         snprintf(newdir, sizeof(newdir), "%s%s", newroot, dir);
  41
  42         if (stat(olddir, &s) || !S_ISDIR(s.st_mode))
  43                 return -1;
  44
  45         if (stat(newdir, &s) || !S_ISDIR(s.st_mode))
  46                 return -1;
  47
  48         ret = mount(olddir, newdir, NULL, MS_NOATIME | MS_MOVE, NULL);
  49
  50 /*      if (ret)
  51                 fprintf(stderr, "failed %s %s: %s\n", olddir, newdir, strerror(errno));*/
  52
  53         return ret;
  54 }
  55
  56 int
  57 pivot(char *new, char *old)
  58 {
  59         char pivotdir[64];
  60         int ret;
  61
  62         if (mount_move("", new, "/proc"))
  63                 return -1;
  64
  65         snprintf(pivotdir, sizeof(pivotdir), "%s%s", new, old);
  66
  67         ret = pivot_root(new, pivotdir);
  68
  69         if (ret < 0) {
  70                 fprintf(stderr, "pivot_root failed %s %s: %s\n", new, pivotdir, strerror(errno));
  71                 return -1;
  72         }
  73
  74         mount_move(old, "", "/dev");
  75         mount_move(old, "", "/tmp");
  76         mount_move(old, "", "/sys");
  77         mount_move(old, "", "/overlay");
  78
  79         return 0;
  80 }
  81
  82 int
  83 fopivot(char *rw_root, char *ro_root)
  84 {
  85         char overlay[64], lowerdir[64];
  86
  87         if (find_filesystem("overlay")) {
  88                 fprintf(stderr, "BUG: no suitable fs found\n");
  89                 return -1;
  90         }
  91
  92         snprintf(overlay, sizeof(overlay), "overlayfs:%s", rw_root);
  93
  94         /*
  95          * First, try to mount without a workdir, for overlayfs v22 and before.
  96          * If it fails, it means that we are probably using a v23 and
  97          * later versions that require a workdir
  98          */
  99         snprintf(lowerdir, sizeof(lowerdir), "lowerdir=/,upperdir=%s", rw_root);
 100         if (mount(overlay, "/mnt", "overlayfs", MS_NOATIME, lowerdir)) {
 101                 char upperdir[64], workdir[64];
 102
 103                 snprintf(upperdir, sizeof(upperdir), "%s/upper", rw_root);
 104                 snprintf(workdir, sizeof(workdir), "%s/work", rw_root);
 105                 snprintf(lowerdir, sizeof(lowerdir), "lowerdir=/,upperdir=%s,workdir=%s",
 106                          upperdir, workdir);
 107
 108                 /*
 109                  * Overlay FS v23 and later requires both a upper and
 110                  * a work directory, both on the same filesystem, but
 111                  * not part of the same subtree.
 112                  * We can't really deal with these constraints without
 113                  * creating two new subdirectories in /overlay.
 114                  */
 115                 mkdir(upperdir, 0755);
 116                 mkdir(workdir, 0755);
 117
 118                 /* Mainlined overlayfs has been renamed to "overlay", try that first */
 119                 if (mount(overlay, "/mnt", "overlay", MS_NOATIME, lowerdir)) {
 120                         if (mount(overlay, "/mnt", "overlayfs", MS_NOATIME, lowerdir)) {
 121                                 fprintf(stderr, "mount failed: %s, options %s\n",
 122                                         strerror(errno), lowerdir);
 123                                 return -1;
 124                         }
 125                 }
 126         }
 127
 128         return pivot("/mnt", ro_root);
 129 }
 130
 131 int
 132 ramoverlay(void)
 133 {
 134         mkdir("/tmp/root", 0755);
 135         mount("tmpfs", "/tmp/root", "tmpfs", MS_NOATIME, "mode=0755");
 136
 137         return fopivot("/tmp/root", "/rom");
 138 }