mirror of
https://github.com/topjohnwu/ndk-busybox.git
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125 lines
2.8 KiB
C
125 lines
2.8 KiB
C
/* vi: set sw=4 ts=4: */
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/* Copyright 2005 Rob Landley <rob@landley.net>
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*
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* Switch from rootfs to another filesystem as the root of the mount tree.
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*
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* Licensed under GPL version 2, see file LICENSE in this tarball for details.
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*/
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#include "libbb.h"
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#include <sys/vfs.h>
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// Make up for header deficiencies.
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#ifndef RAMFS_MAGIC
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#define RAMFS_MAGIC 0x858458f6
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#endif
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#ifndef TMPFS_MAGIC
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#define TMPFS_MAGIC 0x01021994
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#endif
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#ifndef MS_MOVE
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#define MS_MOVE 8192
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#endif
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static dev_t rootdev;
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// Recursively delete contents of rootfs.
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static void delete_contents(const char *directory)
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{
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DIR *dir;
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struct dirent *d;
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struct stat st;
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// Don't descend into other filesystems
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if (lstat(directory, &st) || st.st_dev != rootdev) return;
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// Recursively delete the contents of directories.
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if (S_ISDIR(st.st_mode)) {
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dir = opendir(directory);
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if (dir) {
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while ((d = readdir(dir))) {
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char *newdir = d->d_name;
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// Skip . and ..
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if (*newdir=='.' && (!newdir[1] || (newdir[1]=='.' && !newdir[2])))
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continue;
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// Recurse to delete contents
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newdir = alloca(strlen(directory) + strlen(d->d_name) + 2);
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sprintf(newdir, "%s/%s", directory, d->d_name);
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delete_contents(newdir);
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}
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closedir(dir);
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// Directory should now be empty. Zap it.
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rmdir(directory);
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}
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// It wasn't a directory. Zap it.
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} else unlink(directory);
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}
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int switch_root_main(int argc, char **argv);
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int switch_root_main(int argc, char **argv)
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{
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char *newroot, *console = NULL;
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struct stat st1, st2;
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struct statfs stfs;
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// Parse args (-c console)
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opt_complementary = "-2";
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getopt32(argc, argv, "c:", &console);
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argv += optind;
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// Change to new root directory and verify it's a different fs.
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newroot = *argv++;
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xchdir(newroot);
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if (lstat(".", &st1) || lstat("/", &st2) || st1.st_dev == st2.st_dev) {
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bb_error_msg_and_die("bad newroot %s", newroot);
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}
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rootdev = st2.st_dev;
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// Additional sanity checks: we're about to rm -rf /, so be REALLY SURE
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// we mean it. (I could make this a CONFIG option, but I would get email
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// from all the people who WILL eat their filesystems.)
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if (lstat("/init", &st1) || !S_ISREG(st1.st_mode) || statfs("/", &stfs) ||
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(stfs.f_type != RAMFS_MAGIC && stfs.f_type != TMPFS_MAGIC) ||
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getpid() != 1)
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{
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bb_error_msg_and_die("not rootfs");
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}
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// Zap everything out of rootdev
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delete_contents("/");
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// Overmount / with newdir and chroot into it. The chdir is needed to
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// recalculate "." and ".." links.
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if (mount(".", "/", NULL, MS_MOVE, NULL) || chroot("."))
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bb_error_msg_and_die("error moving root");
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xchdir("/");
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// If a new console specified, redirect stdin/stdout/stderr to that.
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if (console) {
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close(0);
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xopen(console, O_RDWR);
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dup2(0, 1);
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dup2(0, 2);
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}
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// Exec real init. (This is why we must be pid 1.)
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execv(argv[0], argv);
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bb_perror_msg_and_die("bad init %s", argv[0]);
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}
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