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/*
* Copyright (C) 2014 John Crispin <blogic@openwrt.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License version 2.1
* as published by the Free Software Foundation
*
* This program 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 General Public License for more details.
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mount.h>
#include <errno.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include "libfstools.h"
/* this is a raw syscall - man 2 pivot_root */
extern int pivot_root(const char *new_root, const char *put_old);
/**
* mount_move - move mounted point to the new location
*
* @oldroot: directory that is current location of mount point
* @newroot: new directory for the mount point
*/
int
mount_move(const char *oldroot, const char *newroot, const char *dir)
{
#ifndef MS_MOVE
#define MS_MOVE (1 << 13)
#endif
struct stat s;
char olddir[64];
char newdir[64];
int ret;
snprintf(olddir, sizeof(olddir), "%s%s", oldroot, dir);
snprintf(newdir, sizeof(newdir), "%s%s", newroot, dir);
if (stat(olddir, &s) || !S_ISDIR(s.st_mode))
return -1;
if (stat(newdir, &s) || !S_ISDIR(s.st_mode))
return -1;
ret = mount(olddir, newdir, NULL, MS_NOATIME | MS_MOVE, NULL);
/* if (ret)
ULOG_ERR("failed %s %s: %s\n", olddir, newdir, strerror(errno));*/
return ret;
}
int
pivot(char *new, char *old)
{
char pivotdir[64];
int ret;
if (mount_move("", new, "/proc"))
return -1;
snprintf(pivotdir, sizeof(pivotdir), "%s%s", new, old);
ret = pivot_root(new, pivotdir);
if (ret < 0) {
ULOG_ERR("pivot_root failed %s %s: %s\n", new, pivotdir, strerror(errno));
return -1;
}
mount_move(old, "", "/dev");
mount_move(old, "", "/tmp");
mount_move(old, "", "/sys");
mount_move(old, "", "/overlay");
return 0;
}
/**
* fopivot - switch to overlay using passed dir as upper one
*
* @rw_root: writable directory that will be used as upper dir
* @ro_root: directory where old root will be put
*/
int
fopivot(char *rw_root, char *ro_root)
{
char overlay[64], mount_options[64];
if (find_filesystem("overlay")) {
ULOG_ERR("BUG: no suitable fs found\n");
return -1;
}
snprintf(overlay, sizeof(overlay), "overlayfs:%s", rw_root);
/*
* First, try to mount without a workdir, for overlayfs v22 and before.
* If it fails, it means that we are probably using a v23 and
* later versions that require a workdir
*/
snprintf(mount_options, sizeof(mount_options), "lowerdir=/,upperdir=%s", rw_root);
if (mount(overlay, "/mnt", "overlayfs", MS_NOATIME, mount_options)) {
char upperdir[64], workdir[64], upgrade[64], upgrade_dest[64];
struct stat st;
snprintf(upperdir, sizeof(upperdir), "%s/upper", rw_root);
snprintf(workdir, sizeof(workdir), "%s/work", rw_root);
snprintf(upgrade, sizeof(upgrade), "%s/sysupgrade.tgz", rw_root);
snprintf(upgrade_dest, sizeof(upgrade_dest), "%s/sysupgrade.tgz", upperdir);
snprintf(mount_options, sizeof(mount_options), "lowerdir=/,upperdir=%s,workdir=%s",
upperdir, workdir);
/*
* Overlay FS v23 and later requires both a upper and
* a work directory, both on the same filesystem, but
* not part of the same subtree.
* We can't really deal with these constraints without
* creating two new subdirectories in /overlay.
*/
mkdir(upperdir, 0755);
mkdir(workdir, 0755);
if (stat(upgrade, &st) == 0)
rename(upgrade, upgrade_dest);
/* Mainlined overlayfs has been renamed to "overlay", try that first */
if (mount(overlay, "/mnt", "overlay", MS_NOATIME, mount_options)) {
if (mount(overlay, "/mnt", "overlayfs", MS_NOATIME, mount_options)) {
ULOG_ERR("mount failed: %s, options %s\n",
strerror(errno), mount_options);
return -1;
}
}
}
return pivot("/mnt", ro_root);
}
/**
* ramoverlay - use RAM to store filesystem changes on top of RO root
*/
int
ramoverlay(void)
{
mkdir("/tmp/root", 0755);
mount("tmpfs", "/tmp/root", "tmpfs", MS_NOATIME, "mode=0755");
return fopivot("/tmp/root", "/rom");
}
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