switch_root.c revision fec3fd1f8ac1db9ed87b79bd3eb5e38aa835e881 
1/* switch_root.c - Switch from rootfs/initramfs to another filesystem
2 *
3 * Copyright 2005 Rob Landley <rob@landley.net>
4
5USE_SWITCH_ROOT(NEWTOY(switch_root, "<2c:h", TOYFLAG_SBIN))
6
7config SWITCH_ROOT
8  bool "switch_root"
9  default y
10  help
11    usage: switch_root [-c /dev/console] NEW_ROOT NEW_INIT...
12
13    Use from PID 1 under initramfs to free initramfs, chroot to NEW_ROOT,
14    and exec NEW_INIT.
15
16    -c	Redirect console to device in NEW_ROOT
17    -h	Hang instead of exiting on failure (avoids kernel panic)
18*/
19
20#define FOR_switch_root
21#include "toys.h"
22#include <sys/vfs.h>
23
24GLOBALS(
25  char *console;
26
27  dev_t rootdev;
28)
29
30static int del_node(struct dirtree *node)
31{
32  if (node->st.st_dev == TT.rootdev && dirtree_notdotdot(node)) {
33    int flag = 0;
34    if (S_ISDIR(node->st.st_mode)) {
35      if (!node->again) return DIRTREE_COMEAGAIN;
36      flag = AT_REMOVEDIR;
37    }
38    unlinkat(dirtree_parentfd(node), node->name, flag);
39  }
40
41  return 0;
42}
43
44void switch_root_main(void)
45{
46  char *newroot = *toys.optargs, **cmdline = toys.optargs+1;
47  struct stat st1, st2;
48  struct statfs stfs;
49  int console = console; // gcc's "may be used" warnings are broken.
50
51  if (getpid() != 1) error_exit("not pid 1");
52
53  // Root filesystem we're leaving must be ramfs or tmpfs
54  if (statfs("/", &stfs) ||
55    (stfs.f_type != 0x858458f6 && stfs.f_type != 0x01021994))
56  {
57    error_msg("not ramfs");
58    goto panic;
59  }
60
61  // New directory must be different filesystem instance
62  if (chdir(newroot) || stat(".", &st1) || stat("/", &st2) ||
63    st1.st_dev == st2.st_dev)
64  {
65    error_msg("bad newroot '%s'", newroot);
66    goto panic;
67  }
68  TT.rootdev=st2.st_dev;
69
70  // init program must exist and be an executable file
71  if (stat("init", &st1) || !S_ISREG(st1.st_mode) || !(st1.st_mode&0100)) {
72    error_msg("bad init");
73    goto panic;
74  }
75
76  if (TT.console && -1 == (console = open(TT.console, O_RDWR))) {
77    perror_msg("bad console '%s'", TT.console);
78    goto panic;
79  }
80
81  // Ok, enough safety checks: wipe root partition.
82  dirtree_read("/", del_node);
83
84  if (TT.console) {
85    int i;
86    for (i=0; i<3; i++) if (console != i) dup2(console, i);
87    if (console>2) close(console);
88  }
89  execv(*cmdline, cmdline);
90  perror_msg("Failed to exec '%s'", *cmdline);
91panic:
92  if (toys.optflags & FLAG_h) for (;;) wait(NULL);
93}
94