1 /* switch_root.c - Switch from rootfs/initramfs to another filesystem
2 *
3 * Copyright 2005 Rob Landley <rob@landley.net>
4
5 USE_SWITCH_ROOT(NEWTOY(switch_root, "<2c:h", TOYFLAG_SBIN))
6
7 config 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
GLOBALS(char * console;dev_t rootdev;)24 GLOBALS(
25 char *console;
26
27 dev_t rootdev;
28 )
29
30 static 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
switch_root_main(void)44 void 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);
91 panic:
92 if (toys.optflags & FLAG_h) for (;;) wait(NULL);
93 }
94