diff options
| -rw-r--r-- | include/applets.h | 3 | ||||
| -rw-r--r-- | include/usage.h | 6 | ||||
| -rw-r--r-- | util-linux/Config.in | 22 | ||||
| -rw-r--r-- | util-linux/switch_root.c | 118 |
4 files changed, 149 insertions, 0 deletions
diff --git a/include/applets.h b/include/applets.h index a814ce1b1..883e55990 100644 --- a/include/applets.h +++ b/include/applets.h @@ -625,6 +625,9 @@ #ifdef CONFIG_SWAPONOFF APPLET(swapon, swap_on_off_main, _BB_DIR_SBIN, _BB_SUID_NEVER) #endif +#ifdef CONFIG_SWITCH_ROOT + APPLET(switch_root, switch_root_main, _BB_DIR_SBIN, _BB_SUID_NEVER) +#endif #ifdef CONFIG_SYNC APPLET(sync, sync_main, _BB_DIR_BIN, _BB_SUID_NEVER) #endif diff --git a/include/usage.h b/include/usage.h index bef6a4dd2..69c50b97b 100644 --- a/include/usage.h +++ b/include/usage.h @@ -2735,6 +2735,12 @@ "Options:\n" \ "\t-a\tStart swapping on all swap devices" +#define switch_root_trivial_usage \ + "NEW_ROOT NEW_INIT [ARGUMENTS_TO_INIT]" +#define switch_root_full_usage \ + "Use from PID 1 under initramfs to free initramfs, chroot to NEW_ROOT,\n" \ + "and exec NEW_INIT.\n" + #define sync_trivial_usage \ "" #define sync_full_usage \ diff --git a/util-linux/Config.in b/util-linux/Config.in index dc6d8fdad..fe71dac2c 100644 --- a/util-linux/Config.in +++ b/util-linux/Config.in @@ -288,6 +288,28 @@ config CONFIG_PIVOT_ROOT of wild and crazy things with your Linux system and is far more powerful than 'chroot'. + Note: This is for initrd in linux 2.4. Under initramfs (introduced + in linux 2.6) use switch_root instead. + +config CONFIG_SWITCH_ROOT + bool "switch_root" + default n + help + The switch_root utility is used from initramfs to select a new + root device. Under initramfs, you have to use this instead of + pivot_root. (Stop reading here if you don't care why.) + + Booting with initramfs extracts a gzipped cpio archive into rootfs + (which is a variant of ramfs/tmpfs). Because rootfs can't be moved + or unmounted*, pivot_root will not work from initramfs. Instead, + switch_root deletes everything out of rootfs (including itself), + does a mount --move that overmounts rootfs with the new root, and + then execs the specified init program. + + * Because the Linux kernel uses rootfs internally as the starting + and ending point for searching through the kernel's doubly linked + list of active mount points. That's why. + config CONFIG_RDATE bool "rdate" default n diff --git a/util-linux/switch_root.c b/util-linux/switch_root.c new file mode 100644 index 000000000..242699560 --- /dev/null +++ b/util-linux/switch_root.c @@ -0,0 +1,118 @@ +/* vi:set ts=4:*/ + +#include <dirent.h> +#include <fcntl.h> +#include <stdio.h> +#include <sys/mount.h> +#include <sys/stat.h> +#include <sys/types.h> +#include <sys/vfs.h> +#include <unistd.h> + +#include "busybox.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 (stat(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. + printf("rmdir %s\n",directory); // rmdir(directory); + } + + // It wasn't a directory. Zap it. + + } else printf("unlink %s\n",directory); //unlink(directory); +} + +int switch_root_main(int argc, char *argv[]) +{ + char *newroot, *console="/dev/console"; + struct stat st1, st2; + struct statfs stfs; + + // Parse args (-c console) + + bb_opt_complementally="-2"; + bb_getopt_ulflags(argc,argv,"c:",&console); + + // Change to new root directory and verify it's a different fs. + + newroot=argv[optind++]; + + if (chdir(newroot) || stat(".", &st1) || stat("/", &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 (stat("/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 + + if (mount(".", "/", NULL, MS_MOVE, NULL) || chdir("/")) + bb_error_msg_and_die("moving root"); + + // Reopen stdin/stdout/stderr to /dev/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+1); + bb_error_msg_and_die("Bad init '%s'",argv[optind]); +} |