0f34a821a

Rob Landley

2005-10-27

SOURCE BUG Duration: 10s

Subject

Add a switch_root utility (like kconfig's utils/run_init.c, although not actuall using any of that code). This is needed because pivot_root doesn't work right under initramfs. (See the menuconfig help.)

SOURCE BUG

This commit was genuinely broken at the time (not related to our build system): scripts/config/mkconfigs.c (2005-08-01 - 2006-10-05 arasi) uretilen bbconfigopts.h icine .config satirlarini kacissiz, ham newline'larla gömüyordu - gecerli C degildi, busybox'un kendi bb_mkdep araci bile parse edemiyordu (7d219aab7 ile duzeltildi, mkconfigs shell scripte cevrildi)

→ Bu hatanin tam hikayesini ve duzeltme diffini gor

Binary

No binary (build failed)

Architecture & Compiler Flags

Architecture: x86_64-linux-gnu Compiler: gcc (Ubuntu 11.4.0-1ubuntu1~22.04.3) 11.4.0

—

Build Log

(log yok)

Commit Diff GitHub →

include/applets.h +3 -0 include/usage.h +6 -0 util-linux/Config.in +22 -0 util-linux/switch_root.c +118 -0

include/applets.h+3 -0

@@ -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

include/usage.h+6 -0

@@ -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 \

util-linux/Config.in+22 -0

@@ -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

util-linux/switch_root.c+118 -0

@@ -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]);
+	}