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Diffstat (limited to 'util-linux/switch_root.c')
-rw-r--r-- | util-linux/switch_root.c | 122 |
1 files changed, 122 insertions, 0 deletions
diff --git a/util-linux/switch_root.c b/util-linux/switch_root.c new file mode 100644 index 000000000..4c23f69da --- /dev/null +++ b/util-linux/switch_root.c @@ -0,0 +1,122 @@ +/* vi: set sw=4 ts=4: */ +/* Copyright 2005 Rob Landley <rob@landley.net> + * + * Switch from rootfs to another filesystem as the root of the mount tree. + * + * Licensed under GPL version 2, see file LICENSE in this tarball for details. + */ + +#include "busybox.h" +#include <sys/vfs.h> + + +// Make up for header deficiencies. + +#ifndef RAMFS_MAGIC +#define RAMFS_MAGIC 0x858458f6 +#endif + +#ifndef TMPFS_MAGIC +#define TMPFS_MAGIC 0x01021994 +#endif + +#ifndef MS_MOVE +#define MS_MOVE 8192 +#endif + +dev_t rootdev; + +// Recursively delete contents of rootfs. + +static void delete_contents(char *directory) +{ + DIR *dir; + struct dirent *d; + struct stat st; + + // Don't descend into other filesystems + if (lstat(directory, &st) || st.st_dev != rootdev) return; + + // Recursively delete the contents of directories. + if (S_ISDIR(st.st_mode)) { + if((dir = opendir(directory))) { + while ((d = readdir(dir))) { + char *newdir=d->d_name; + + // Skip . and .. + if(*newdir=='.' && (!newdir[1] || (newdir[1]=='.' && !newdir[2]))) + continue; + + // Recurse to delete contents + newdir = alloca(strlen(directory) + strlen(d->d_name) + 2); + sprintf(newdir, "%s/%s", directory, d->d_name); + delete_contents(newdir); + } + closedir(dir); + + // Directory should now be empty. Zap it. + rmdir(directory); + } + + // It wasn't a directory. Zap it. + + } else unlink(directory); +} + +int switch_root_main(int argc, char *argv[]) +{ + char *newroot, *console=NULL; + struct stat st1, st2; + struct statfs stfs; + + // Parse args (-c console) + + opt_complementary = "-2"; + getopt32(argc, argv, "c:", &console); + + // Change to new root directory and verify it's a different fs. + + newroot=argv[optind++]; + + if (chdir(newroot) || lstat(".", &st1) || lstat("/", &st2) || + st1.st_dev == st2.st_dev) + { + bb_error_msg_and_die("bad newroot %s", newroot); + } + rootdev=st2.st_dev; + + // Additional sanity checks: we're about to rm -rf /, so be REALLY SURE + // we mean it. (I could make this a CONFIG option, but I would get email + // from all the people who WILL eat their filesystemss.) + + if (lstat("/init", &st1) || !S_ISREG(st1.st_mode) || statfs("/", &stfs) || + (stfs.f_type != RAMFS_MAGIC && stfs.f_type != TMPFS_MAGIC) || + getpid() != 1) + { + bb_error_msg_and_die("not rootfs"); + } + + // Zap everything out of rootdev + + delete_contents("/"); + + // Overmount / with newdir and chroot into it. The chdir is needed to + // recalculate "." and ".." links. + + if (mount(".", "/", NULL, MS_MOVE, NULL) || chroot(".") || chdir("/")) + bb_error_msg_and_die("moving root"); + + // If a new console specified, redirect stdin/stdout/stderr to that. + + if (console) { + close(0); + if(open(console, O_RDWR) < 0) + bb_error_msg_and_die("bad console '%s'", console); + dup2(0, 1); + dup2(0, 2); + } + + // Exec real init. (This is why we must be pid 1.) + execv(argv[optind], argv+optind); + bb_error_msg_and_die("bad init '%s'", argv[optind]); +} |