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comparison toys/other/switch_root.c @ 664:c60ac785784f

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Add switch_root and fix infrastructure to understand name "switch_root".
author Rob Landley <rob@landley.net>
date Sat, 08 Sep 2012 01:27:54 -0500
parents
children 7e846e281e38
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663:60cbc87c4314 664:c60ac785784f
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 #include "toys.h"
21 #include <sys/vfs.h>
22
23 DEFINE_GLOBALS(
24 char *console;
25
26 dev_t rootdev;
27 )
28
29 #define TT this.switch_root
30
31 #define FLAG_h (1<<0)
32 #define FLAG_c (1<<1)
33
34 static int del_node(struct dirtree *node)
35 {
36 if (node->st.st_dev == TT.rootdev && dirtree_notdotdot(node)) {
37 int flag = 0;
38 if (S_ISDIR(node->st.st_mode)) {
39 if (node->data != -1) return DIRTREE_COMEAGAIN;
40 flag = AT_REMOVEDIR;
41 }
42 unlinkat(dirtree_parentfd(node), node->name, flag);
43 }
44
45 return 0;
46 }
47
48 void switch_root_main(void)
49 {
50 char *newroot = *toys.optargs, **cmdline = toys.optargs+1;
51 struct stat st1, st2;
52 struct statfs stfs;
53 int console = console; // gcc's "may be used" warnings are broken.
54
55 if (getpid() != 1) error_exit("not pid 1");
56
57 // Root filesystem we're leaving must be ramfs or tmpfs
58 if (statfs("/", &stfs) ||
59 (stfs.f_type != 0x858458f6 && stfs.f_type != 0x01021994))
60 {
61 error_msg("not ramfs");
62 goto panic;
63 }
64
65 // New directory must be different filesystem instance
66 if (chdir(newroot) || stat(".", &st1) || stat("/", &st2) ||
67 st1.st_dev == st2.st_dev)
68 {
69 error_msg("bad newroot '%s'", newroot);
70 goto panic;
71 }
72 TT.rootdev=st2.st_dev;
73
74 // init program must exist and be an executable file
75 if (stat("init", &st1) || !S_ISREG(st1.st_mode) || !(st1.st_mode&0100)) {
76 error_msg("bad init");
77 goto panic;
78 }
79
80 if (TT.console && -1 == (console = open(TT.console, O_RDWR))) {
81 perror_msg("bad console '%s'", TT.console);
82 goto panic;
83 }
84
85 // Ok, enough safety checks: wipe root partition.
86 dirtree_read("/", del_node);
87
88 if (TT.console) {
89 int i;
90 for (i=0; i<3; i++) if (console != i) dup2(console, i);
91 if (console>2) close(console);
92 }
93 execv(*cmdline, cmdline);
94 perror_msg("Failed to exec '%s'", *cmdline);
95 panic:
96 if (toys.optflags & FLAG_h) for (;;) wait(NULL);
97 }