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annotate 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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664
c60ac785784f Add switch_root and fix infrastructure to understand name "switch_root".
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1 /* switch_root.c - Switch from rootfs/initramfs to another filesystem
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2 *
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3 * Copyright 2005 Rob Landley <rob@landley.net>
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4
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5 USE_SWITCH_ROOT(NEWTOY(switch_root, "<2c:h", TOYFLAG_SBIN))
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6
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7 config SWITCH_ROOT
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8 bool "switch_root"
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9 default y
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10 help
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11 usage: switch_root [-c /dev/console] NEW_ROOT NEW_INIT...
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12
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13 Use from PID 1 under initramfs to free initramfs, chroot to NEW_ROOT,
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14 and exec NEW_INIT.
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15
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16 -c Redirect console to device in NEW_ROOT
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17 -h Hang instead of exiting on failure (avoids kernel panic)
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18 */
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19
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20 #include "toys.h"
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21 #include <sys/vfs.h>
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22
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23 DEFINE_GLOBALS(
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24 char *console;
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25
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26 dev_t rootdev;
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27 )
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28
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29 #define TT this.switch_root
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30
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31 #define FLAG_h (1<<0)
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32 #define FLAG_c (1<<1)
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33
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34 static int del_node(struct dirtree *node)
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35 {
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36 if (node->st.st_dev == TT.rootdev && dirtree_notdotdot(node)) {
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37 int flag = 0;
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38 if (S_ISDIR(node->st.st_mode)) {
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39 if (node->data != -1) return DIRTREE_COMEAGAIN;
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40 flag = AT_REMOVEDIR;
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41 }
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42 unlinkat(dirtree_parentfd(node), node->name, flag);
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43 }
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44
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45 return 0;
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46 }
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47
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48 void switch_root_main(void)
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49 {
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50 char *newroot = *toys.optargs, **cmdline = toys.optargs+1;
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51 struct stat st1, st2;
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52 struct statfs stfs;
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53 int console = console; // gcc's "may be used" warnings are broken.
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54
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55 if (getpid() != 1) error_exit("not pid 1");
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56
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57 // Root filesystem we're leaving must be ramfs or tmpfs
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58 if (statfs("/", &stfs) ||
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59 (stfs.f_type != 0x858458f6 && stfs.f_type != 0x01021994))
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60 {
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61 error_msg("not ramfs");
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62 goto panic;
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63 }
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64
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65 // New directory must be different filesystem instance
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66 if (chdir(newroot) || stat(".", &st1) || stat("/", &st2) ||
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67 st1.st_dev == st2.st_dev)
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68 {
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69 error_msg("bad newroot '%s'", newroot);
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70 goto panic;
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71 }
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72 TT.rootdev=st2.st_dev;
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73
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74 // init program must exist and be an executable file
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75 if (stat("init", &st1) || !S_ISREG(st1.st_mode) || !(st1.st_mode&0100)) {
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76 error_msg("bad init");
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77 goto panic;
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78 }
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79
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80 if (TT.console && -1 == (console = open(TT.console, O_RDWR))) {
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81 perror_msg("bad console '%s'", TT.console);
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82 goto panic;
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83 }
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84
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85 // Ok, enough safety checks: wipe root partition.
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86 dirtree_read("/", del_node);
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87
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88 if (TT.console) {
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89 int i;
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90 for (i=0; i<3; i++) if (console != i) dup2(console, i);
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91 if (console>2) close(console);
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92 }
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93 execv(*cmdline, cmdline);
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94 perror_msg("Failed to exec '%s'", *cmdline);
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95 panic:
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96 if (toys.optflags & FLAG_h) for (;;) wait(NULL);
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97 }