void __init mount_block_root(char *name, int flags)
{
	struct page *page = alloc_page(GFP_KERNEL |
					__GFP_NOTRACK_FALSE_POSITIVE);
	char *fs_names = page_address(page);
	char *p;
#ifdef CONFIG_BLOCK
	char b[BDEVNAME_SIZE];
#else
	const char *b = name;
#endif

	get_fs_names(fs_names);
retry:
	for (p = fs_names; *p; p += strlen(p)+1) {
		int err = do_mount_root(name, p, flags, root_mount_data);
		switch (err) {
			case 0:
				goto out;
			case -EACCES:
			case -EINVAL:
				continue;
		}
	        /*
		 * Allow the user to distinguish between failed sys_open
		 * and bad superblock on root device.
		 * and give them a list of the available devices
		 */
#ifdef CONFIG_BLOCK
		__bdevname(ROOT_DEV, b);
#endif
		printk("VFS: Cannot open root device \"%s\" or %s: error %d\n",
				root_device_name, b, err);
		printk("Please append a correct \"root=\" boot option; here are the available partitions:\n");

		printk_all_partitions();
#ifdef CONFIG_DEBUG_BLOCK_EXT_DEVT
		printk("DEBUG_BLOCK_EXT_DEVT is enabled, you need to specify "
		       "explicit textual name for \"root=\" boot option.\n");
#endif
		panic("VFS: Unable to mount root fs on %s", b);
	}
	if (!(flags & MS_RDONLY)) {
		flags |= MS_RDONLY;
		goto retry;
	}

	printk("List of all partitions:\n");
	printk_all_partitions();
	printk("No filesystem could mount root, tried: ");
	for (p = fs_names; *p; p += strlen(p)+1)
		printk(" %s", p);
	printk("\n");
#ifdef CONFIG_BLOCK
	__bdevname(ROOT_DEV, b);
#endif
	panic("VFS: Unable to mount root fs on %s", b);
out:
	put_page(page);
}

int change_root(kdev_t new_root_dev,const char *put_old)
{
	kdev_t old_root_dev;
	struct vfsmount *vfsmnt;
	struct inode *old_root,*old_pwd,*inode;
	unsigned long old_fs;
	int error;

	old_root = current->fs->root;
	old_pwd = current->fs->pwd;
	old_root_dev = ROOT_DEV;
	if (!fs_may_mount(new_root_dev)) {
		printk(KERN_CRIT "New root is busy. Staying in initrd.\n");
		return -EBUSY;
	}
	ROOT_DEV = new_root_dev;
	do_mount_root();
	old_fs = get_fs();
	set_fs(get_ds());
        error = namei(put_old,&inode);
	if (error) inode = NULL;
	set_fs(old_fs);
	if (!error && (inode->i_count != 1 || inode->i_mount)) error = -EBUSY;
	if (!error && !S_ISDIR(inode->i_mode)) error = -ENOTDIR;
	iput(old_root); /* current->fs->root */
	iput(old_pwd); /* current->fs->pwd */
	if (error) {
		int umount_error;

		if (inode) iput(inode);
		printk(KERN_NOTICE "Trying to unmount old root ... ");
		old_root->i_mount = old_root;
			/* does this belong into do_mount_root ? */
		umount_error = do_umount(old_root_dev,1);
		if (umount_error) printk(KERN_ERR "error %d\n",umount_error);
		else {
			printk(KERN_NOTICE "okay\n");
			invalidate_buffers(old_root_dev);
		}
		return umount_error ? error : 0;
	}
	iput(old_root); /* sb->s_covered */
	remove_vfsmnt(old_root_dev);
	vfsmnt = add_vfsmnt(old_root_dev,"old_rootfs",put_old);
	if (!vfsmnt) printk(KERN_CRIT "Trouble: add_vfsmnt failed\n");
	else {
		vfsmnt->mnt_sb = old_root->i_sb;
		vfsmnt->mnt_sb->s_covered = inode;
		vfsmnt->mnt_flags = vfsmnt->mnt_sb->s_flags;
	}
	inode->i_mount = old_root;
	return 0;
}

void __init mount_block_root(char *name, int flags)
{
	char *fs_names = __getname();
	char *p;
#ifdef CONFIG_BLOCK
	char b[BDEVNAME_SIZE];
#else
	const char *b = name;
#endif

	get_fs_names(fs_names);
retry:
	for (p = fs_names; *p; p += strlen(p)+1) {
		int err = do_mount_root(name, p, flags, root_mount_data);
		switch (err) {
			case 0:
				goto out;
			case -EACCES:
				flags |= MS_RDONLY;
				goto retry;
			case -EINVAL:
				continue;
		}
	        /*
		 * Allow the user to distinguish between failed sys_open
		 * and bad superblock on root device.
		 * and give them a list of the available devices
		 */
#ifdef CONFIG_BLOCK
		__bdevname(ROOT_DEV, b);
#endif
		printk("VFS: Cannot open root device \"%s\" or %s\n",
				root_device_name, b);
		printk("Please append a correct \"root=\" boot option; here are the available partitions:\n");

		printk_all_partitions();
		panic("VFS: Unable to mount root fs on %s", b);
	}

	printk("List of all partitions:\n");
	printk_all_partitions();
	printk("No filesystem could mount root, tried: ");
	for (p = fs_names; *p; p += strlen(p)+1)
		printk(" %s", p);
	printk("\n");
#ifdef CONFIG_BLOCK
	__bdevname(ROOT_DEV, b);
#endif
	panic("VFS: Unable to mount root fs on %s", b);
out:
	putname(fs_names);
}

static int __init mount_ubi_rootfs(void)
{
	int flags = MS_SILENT;
	int err, tried = 0;

	while (tried < 2) {
		err = do_mount_root("ubi0:rootfs", "ubifs", flags, \
					root_mount_data);
		switch (err) {
			case -EACCES:
				flags |= MS_RDONLY;
				tried++;
			default:
				return err;
		}
	}

	return -EINVAL;
}

static int __init mount_nfs_root(void)
{
	char *root_dev, *root_data;
	unsigned int timeout;
	int try, err;

	err = nfs_root_data(&root_dev, &root_data);
	if (err != 0)
		return 0;

	/*
	 * The server or network may not be ready, so try several
	 * times.  Stop after a few tries in case the client wants
	 * to fall back to other boot methods.
	 */
	timeout = NFSROOT_TIMEOUT_MIN;
	for (try = 1; ; try++) {
		err = do_mount_root(root_dev, "nfs",
					root_mountflags, root_data);
		if (err == 0)
			return 1;
		if (try > NFSROOT_RETRY_MAX)
			break;

		/* Wait, in case the server refused us immediately */
		ssleep(timeout);
		timeout <<= 1;
		if (timeout > NFSROOT_TIMEOUT_MAX)
			timeout = NFSROOT_TIMEOUT_MAX;
	}
	return 0;
}
#endif

#if defined(CONFIG_BLK_DEV_RAM) || defined(CONFIG_BLK_DEV_FD)
void __init change_floppy(char *fmt, ...)
{
	struct termios termios;
	char buf[80];
	char c;
	int fd;
	va_list args;
	va_start(args, fmt);
	vsprintf(buf, fmt, args);
	va_end(args);
	fd = sys_open("/dev/root", O_RDWR | O_NDELAY, 0);
	if (fd >= 0) {
		sys_ioctl(fd, FDEJECT, 0);
		sys_close(fd);
	}
	printk(KERN_NOTICE "VFS: Insert %s and press ENTER\n", buf);
	fd = sys_open("/dev/console", O_RDWR, 0);
	if (fd >= 0) {
		sys_ioctl(fd, TCGETS, (long)&termios);
		termios.c_lflag &= ~ICANON;
		sys_ioctl(fd, TCSETSF, (long)&termios);
		sys_read(fd, &c, 1);
		termios.c_lflag |= ICANON;
		sys_ioctl(fd, TCSETSF, (long)&termios);
		sys_close(fd);
	}
}
#endif

void __init mount_root(void)
{
#ifdef CONFIG_ROOT_NFS
	if (ROOT_DEV == Root_NFS) {
		if (mount_nfs_root())
			return;

		printk(KERN_ERR "VFS: Unable to mount root fs via NFS, trying floppy.\n");
		ROOT_DEV = Root_FD0;
	}
#endif
#ifdef CONFIG_BLK_DEV_FD
	if (MAJOR(ROOT_DEV) == FLOPPY_MAJOR) {
		/* rd_doload is 2 for a dual initrd/ramload setup */
		if (rd_doload==2) {
			if (rd_load_disk(1)) {
				ROOT_DEV = Root_RAM1;
				root_device_name = NULL;
			}
		} else
			change_floppy("root floppy");
	}
#endif
#ifdef CONFIG_BLOCK
	create_dev("/dev/root", ROOT_DEV);
	mount_block_root("/dev/root", root_mountflags);
#endif
}

/*
 * Prepare the namespace - decide what/where to mount, load ramdisks, etc.
 */
void __init prepare_namespace(void)
{
	int is_floppy;

//.........这里部分代码省略.........

void mount_root(void)
{
	memset(super_blocks, 0, sizeof(super_blocks));
	do_mount_root();
}