source: trunk/mindi-busybox/util-linux/switch_root.c @ 956

Last change on this file since 956 was 821, checked in by bruno, 13 years ago

Addition of busybox 1.2.1 as a mindi-busybox new package
This should avoid delivering binary files in mindi not built there (Fedora and Debian are quite serious about that)

File size: 2.9 KB
Line 
1/* vi:set ts=4:*/
2/* Copyright 2005 Rob Landley <rob@landley.net>
3 *
4 * Switch from rootfs to another filesystem as the root of the mount tree.
5 *
6 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
7 */
8
9#include "busybox.h"
10#include <fcntl.h>
11#include <string.h>
12#include <sys/vfs.h>
13#include <unistd.h>
14
15
16// Make up for header deficiencies.
17
18#ifndef RAMFS_MAGIC
19#define RAMFS_MAGIC     0x858458f6
20#endif
21
22#ifndef TMPFS_MAGIC
23#define TMPFS_MAGIC     0x01021994
24#endif
25
26#ifndef MS_MOVE
27#define MS_MOVE         8192
28#endif
29
30dev_t rootdev;
31
32// Recursively delete contents of rootfs.
33
34static void delete_contents(char *directory)
35{
36    DIR *dir;
37    struct dirent *d;
38    struct stat st;
39
40    // Don't descend into other filesystems
41    if (lstat(directory,&st) || st.st_dev != rootdev) return;
42
43    // Recursively delete the contents of directories.
44    if (S_ISDIR(st.st_mode)) {
45        if((dir = opendir(directory))) {
46            while ((d = readdir(dir))) {
47                char *newdir=d->d_name;
48
49                // Skip . and ..
50                if(*newdir=='.' && (!newdir[1] || (newdir[1]=='.' && !newdir[2])))
51                    continue;
52
53                // Recurse to delete contents
54                newdir = alloca(strlen(directory) + strlen(d->d_name) + 2);
55                sprintf(newdir, "%s/%s", directory, d->d_name);
56                delete_contents(newdir);
57            }
58            closedir(dir);
59
60            // Directory should now be empty.  Zap it.
61            rmdir(directory);
62        }
63
64    // It wasn't a directory.  Zap it.
65
66    } else unlink(directory);
67}
68
69int switch_root_main(int argc, char *argv[])
70{
71    char *newroot, *console=NULL;
72    struct stat st1, st2;
73    struct statfs stfs;
74
75    // Parse args (-c console)
76
77    bb_opt_complementally="-2";
78    bb_getopt_ulflags(argc,argv,"c:",&console);
79
80    // Change to new root directory and verify it's a different fs.
81
82    newroot=argv[optind++];
83
84    if (chdir(newroot) || lstat(".", &st1) || lstat("/", &st2) ||
85        st1.st_dev == st2.st_dev)
86    {
87        bb_error_msg_and_die("bad newroot %s",newroot);
88    }
89    rootdev=st2.st_dev;
90
91    // Additional sanity checks: we're about to rm -rf /,  so be REALLY SURE
92    // we mean it.  (I could make this a CONFIG option, but I would get email
93    // from all the people who WILL eat their filesystemss.)
94
95    if (lstat("/init", &st1) || !S_ISREG(st1.st_mode) || statfs("/", &stfs) ||
96        (stfs.f_type != RAMFS_MAGIC && stfs.f_type != TMPFS_MAGIC) ||
97        getpid() != 1)
98    {
99        bb_error_msg_and_die("not rootfs");
100    }
101
102    // Zap everything out of rootdev
103
104    delete_contents("/");
105
106    // Overmount / with newdir and chroot into it.  The chdir is needed to
107    // recalculate "." and ".." links.
108
109    if (mount(".", "/", NULL, MS_MOVE, NULL) || chroot(".") || chdir("/"))
110        bb_error_msg_and_die("moving root");
111
112    // If a new console specified, redirect stdin/stdout/stderr to that.
113
114    if (console) {
115        close(0);
116        if(open(console, O_RDWR) < 0)
117            bb_error_msg_and_die("Bad console '%s'",console);
118        dup2(0, 1);
119        dup2(0, 2);
120    }
121
122    // Exec real init.  (This is why we must be pid 1.)
123    execv(argv[optind],argv+optind);
124    bb_error_msg_and_die("Bad init '%s'",argv[optind]);
125}
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