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32 results

i2o_block.c

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  • namespace.c 35.25 KiB
    /*
     *  linux/fs/namespace.c
     *
     * (C) Copyright Al Viro 2000, 2001
     *	Released under GPL v2.
     *
     * Based on code from fs/super.c, copyright Linus Torvalds and others.
     * Heavily rewritten.
     */
    
    #include <linux/config.h>
    #include <linux/syscalls.h>
    #include <linux/slab.h>
    #include <linux/sched.h>
    #include <linux/smp_lock.h>
    #include <linux/init.h>
    #include <linux/quotaops.h>
    #include <linux/acct.h>
    #include <linux/module.h>
    #include <linux/seq_file.h>
    #include <linux/namespace.h>
    #include <linux/namei.h>
    #include <linux/security.h>
    #include <linux/mount.h>
    #include <asm/uaccess.h>
    #include <asm/unistd.h>
    
    extern int __init init_rootfs(void);
    
    #ifdef CONFIG_SYSFS
    extern int __init sysfs_init(void);
    #else
    static inline int sysfs_init(void)
    {
    	return 0;
    }
    #endif
    
    /* spinlock for vfsmount related operations, inplace of dcache_lock */
     __cacheline_aligned_in_smp DEFINE_SPINLOCK(vfsmount_lock);
    
    static struct list_head *mount_hashtable;
    static int hash_mask __read_mostly, hash_bits __read_mostly;
    static kmem_cache_t *mnt_cache; 
    
    static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
    {
    	unsigned long tmp = ((unsigned long) mnt / L1_CACHE_BYTES);
    	tmp += ((unsigned long) dentry / L1_CACHE_BYTES);
    	tmp = tmp + (tmp >> hash_bits);
    	return tmp & hash_mask;
    }
    
    struct vfsmount *alloc_vfsmnt(const char *name)
    {
    	struct vfsmount *mnt = kmem_cache_alloc(mnt_cache, GFP_KERNEL); 
    	if (mnt) {
    		memset(mnt, 0, sizeof(struct vfsmount));
    		atomic_set(&mnt->mnt_count,1);
    		INIT_LIST_HEAD(&mnt->mnt_hash);
    		INIT_LIST_HEAD(&mnt->mnt_child);
    		INIT_LIST_HEAD(&mnt->mnt_mounts);
    		INIT_LIST_HEAD(&mnt->mnt_list);
    		INIT_LIST_HEAD(&mnt->mnt_expire);
    		if (name) {
    			int size = strlen(name)+1;
    			char *newname = kmalloc(size, GFP_KERNEL);
    			if (newname) {
    				memcpy(newname, name, size);
    				mnt->mnt_devname = newname;
    			}
    		}
    	}
    	return mnt;
    }
    
    void free_vfsmnt(struct vfsmount *mnt)
    {
    	kfree(mnt->mnt_devname);
    	kmem_cache_free(mnt_cache, mnt);
    }
    
    /*
     * Now, lookup_mnt increments the ref count before returning
     * the vfsmount struct.
     */
    struct vfsmount *lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
    {
    	struct list_head * head = mount_hashtable + hash(mnt, dentry);
    	struct list_head * tmp = head;
    	struct vfsmount *p, *found = NULL;
    
    	spin_lock(&vfsmount_lock);
    	for (;;) {
    		tmp = tmp->next;
    		p = NULL;
    		if (tmp == head)
    			break;
    		p = list_entry(tmp, struct vfsmount, mnt_hash);
    		if (p->mnt_parent == mnt && p->mnt_mountpoint == dentry) {
    			found = mntget(p);
    			break;
    		}
    	}
    	spin_unlock(&vfsmount_lock);
    	return found;
    }
    
    static inline int check_mnt(struct vfsmount *mnt)
    {
    	return mnt->mnt_namespace == current->namespace;
    }
    
    static void detach_mnt(struct vfsmount *mnt, struct nameidata *old_nd)
    {
    	old_nd->dentry = mnt->mnt_mountpoint;
    	old_nd->mnt = mnt->mnt_parent;
    	mnt->mnt_parent = mnt;
    	mnt->mnt_mountpoint = mnt->mnt_root;
    	list_del_init(&mnt->mnt_child);
    	list_del_init(&mnt->mnt_hash);
    	old_nd->dentry->d_mounted--;
    }
    
    static void attach_mnt(struct vfsmount *mnt, struct nameidata *nd)
    {
    	mnt->mnt_parent = mntget(nd->mnt);
    	mnt->mnt_mountpoint = dget(nd->dentry);
    	list_add(&mnt->mnt_hash, mount_hashtable+hash(nd->mnt, nd->dentry));
    	list_add_tail(&mnt->mnt_child, &nd->mnt->mnt_mounts);
    	nd->dentry->d_mounted++;
    }
    
    static struct vfsmount *next_mnt(struct vfsmount *p, struct vfsmount *root)
    {
    	struct list_head *next = p->mnt_mounts.next;
    	if (next == &p->mnt_mounts) {
    		while (1) {
    			if (p == root)
    				return NULL;
    			next = p->mnt_child.next;
    			if (next != &p->mnt_parent->mnt_mounts)
    				break;
    			p = p->mnt_parent;
    		}
    	}
    	return list_entry(next, struct vfsmount, mnt_child);
    }
    
    static struct vfsmount *
    clone_mnt(struct vfsmount *old, struct dentry *root)
    {
    	struct super_block *sb = old->mnt_sb;
    	struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
    
    	if (mnt) {
    		mnt->mnt_flags = old->mnt_flags;
    		atomic_inc(&sb->s_active);
    		mnt->mnt_sb = sb;
    		mnt->mnt_root = dget(root);
    		mnt->mnt_mountpoint = mnt->mnt_root;
    		mnt->mnt_parent = mnt;
    		mnt->mnt_namespace = current->namespace;
    
    		/* stick the duplicate mount on the same expiry list
    		 * as the original if that was on one */
    		spin_lock(&vfsmount_lock);
    		if (!list_empty(&old->mnt_expire))
    			list_add(&mnt->mnt_expire, &old->mnt_expire);
    		spin_unlock(&vfsmount_lock);
    	}
    	return mnt;
    }
    
    static inline void __mntput(struct vfsmount *mnt)
    {
    	struct super_block *sb = mnt->mnt_sb;
    	dput(mnt->mnt_root);
    	free_vfsmnt(mnt);
    	deactivate_super(sb);
    }
    
    void mntput_no_expire(struct vfsmount *mnt)
    {
    repeat:
    	if (atomic_dec_and_lock(&mnt->mnt_count, &vfsmount_lock)) {
    		if (likely(!mnt->mnt_pinned)) {
    			spin_unlock(&vfsmount_lock);
    			__mntput(mnt);
    			return;
    		}
    		atomic_add(mnt->mnt_pinned + 1, &mnt->mnt_count);
    		mnt->mnt_pinned = 0;
    		spin_unlock(&vfsmount_lock);
    		acct_auto_close_mnt(mnt);
    		security_sb_umount_close(mnt);
    		goto repeat;
    	}
    }
    
    EXPORT_SYMBOL(mntput_no_expire);
    
    void mnt_pin(struct vfsmount *mnt)
    {
    	spin_lock(&vfsmount_lock);
    	mnt->mnt_pinned++;
    	spin_unlock(&vfsmount_lock);
    }
    
    EXPORT_SYMBOL(mnt_pin);
    
    void mnt_unpin(struct vfsmount *mnt)
    {
    	spin_lock(&vfsmount_lock);
    	if (mnt->mnt_pinned) {
    		atomic_inc(&mnt->mnt_count);
    		mnt->mnt_pinned--;
    	}
    	spin_unlock(&vfsmount_lock);
    }
    
    EXPORT_SYMBOL(mnt_unpin);
    
    /* iterator */
    static void *m_start(struct seq_file *m, loff_t *pos)
    {
    	struct namespace *n = m->private;
    	struct list_head *p;
    	loff_t l = *pos;
    
    	down_read(&n->sem);
    	list_for_each(p, &n->list)
    		if (!l--)
    			return list_entry(p, struct vfsmount, mnt_list);
    	return NULL;
    }
    
    static void *m_next(struct seq_file *m, void *v, loff_t *pos)
    {
    	struct namespace *n = m->private;
    	struct list_head *p = ((struct vfsmount *)v)->mnt_list.next;
    	(*pos)++;
    	return p==&n->list ? NULL : list_entry(p, struct vfsmount, mnt_list);
    }
    
    static void m_stop(struct seq_file *m, void *v)
    {
    	struct namespace *n = m->private;
    	up_read(&n->sem);
    }
    
    static inline void mangle(struct seq_file *m, const char *s)
    {
    	seq_escape(m, s, " \t\n\\");
    }
    
    static int show_vfsmnt(struct seq_file *m, void *v)
    {
    	struct vfsmount *mnt = v;
    	int err = 0;
    	static struct proc_fs_info {
    		int flag;
    		char *str;
    	} fs_info[] = {
    		{ MS_SYNCHRONOUS, ",sync" },
    		{ MS_DIRSYNC, ",dirsync" },
    		{ MS_MANDLOCK, ",mand" },
    		{ MS_NOATIME, ",noatime" },
    		{ MS_NODIRATIME, ",nodiratime" },
    		{ 0, NULL }
    	};
    	static struct proc_fs_info mnt_info[] = {
    		{ MNT_NOSUID, ",nosuid" },
    		{ MNT_NODEV, ",nodev" },
    		{ MNT_NOEXEC, ",noexec" },
    		{ 0, NULL }
    	};
    	struct proc_fs_info *fs_infop;
    
    	mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
    	seq_putc(m, ' ');
    	seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
    	seq_putc(m, ' ');
    	mangle(m, mnt->mnt_sb->s_type->name);
    	seq_puts(m, mnt->mnt_sb->s_flags & MS_RDONLY ? " ro" : " rw");
    	for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
    		if (mnt->mnt_sb->s_flags & fs_infop->flag)
    			seq_puts(m, fs_infop->str);
    	}
    	for (fs_infop = mnt_info; fs_infop->flag; fs_infop++) {
    		if (mnt->mnt_flags & fs_infop->flag)
    			seq_puts(m, fs_infop->str);
    	}
    	if (mnt->mnt_sb->s_op->show_options)
    		err = mnt->mnt_sb->s_op->show_options(m, mnt);
    	seq_puts(m, " 0 0\n");
    	return err;
    }
    
    struct seq_operations mounts_op = {
    	.start	= m_start,
    	.next	= m_next,
    	.stop	= m_stop,
    	.show	= show_vfsmnt
    };
    
    /**
     * may_umount_tree - check if a mount tree is busy
     * @mnt: root of mount tree
     *
     * This is called to check if a tree of mounts has any
     * open files, pwds, chroots or sub mounts that are
     * busy.
     */
    int may_umount_tree(struct vfsmount *mnt)
    {
    	struct list_head *next;
    	struct vfsmount *this_parent = mnt;
    	int actual_refs;
    	int minimum_refs;
    
    	spin_lock(&vfsmount_lock);
    	actual_refs = atomic_read(&mnt->mnt_count);
    	minimum_refs = 2;
    repeat:
    	next = this_parent->mnt_mounts.next;
    resume:
    	while (next != &this_parent->mnt_mounts) {
    		struct vfsmount *p = list_entry(next, struct vfsmount, mnt_child);
    
    		next = next->next;
    
    		actual_refs += atomic_read(&p->mnt_count);
    		minimum_refs += 2;
    
    		if (!list_empty(&p->mnt_mounts)) {
    			this_parent = p;
    			goto repeat;
    		}
    	}
    
    	if (this_parent != mnt) {
    		next = this_parent->mnt_child.next;
    		this_parent = this_parent->mnt_parent;
    		goto resume;
    	}
    	spin_unlock(&vfsmount_lock);
    
    	if (actual_refs > minimum_refs)
    		return -EBUSY;
    
    	return 0;
    }
    
    EXPORT_SYMBOL(may_umount_tree);
    
    /**
     * may_umount - check if a mount point is busy
     * @mnt: root of mount
     *
     * This is called to check if a mount point has any
     * open files, pwds, chroots or sub mounts. If the
     * mount has sub mounts this will return busy
     * regardless of whether the sub mounts are busy.
     *
     * Doesn't take quota and stuff into account. IOW, in some cases it will
     * give false negatives. The main reason why it's here is that we need
     * a non-destructive way to look for easily umountable filesystems.
     */
    int may_umount(struct vfsmount *mnt)
    {
    	if (atomic_read(&mnt->mnt_count) > 2)
    		return -EBUSY;
    	return 0;
    }
    
    EXPORT_SYMBOL(may_umount);
    
    static void umount_tree(struct vfsmount *mnt)
    {
    	struct vfsmount *p;
    	LIST_HEAD(kill);
    
    	for (p = mnt; p; p = next_mnt(p, mnt)) {
    		list_del(&p->mnt_list);
    		list_add(&p->mnt_list, &kill);
    		p->mnt_namespace = NULL;
    	}
    
    	while (!list_empty(&kill)) {
    		mnt = list_entry(kill.next, struct vfsmount, mnt_list);
    		list_del_init(&mnt->mnt_list);
    		list_del_init(&mnt->mnt_expire);
    		if (mnt->mnt_parent == mnt) {
    			spin_unlock(&vfsmount_lock);
    		} else {
    			struct nameidata old_nd;
    			detach_mnt(mnt, &old_nd);
    			spin_unlock(&vfsmount_lock);
    			path_release(&old_nd);
    		}
    		mntput(mnt);
    		spin_lock(&vfsmount_lock);
    	}
    }
    
    static int do_umount(struct vfsmount *mnt, int flags)
    {
    	struct super_block * sb = mnt->mnt_sb;
    	int retval;
    
    	retval = security_sb_umount(mnt, flags);
    	if (retval)
    		return retval;
    
    	/*
    	 * Allow userspace to request a mountpoint be expired rather than
    	 * unmounting unconditionally. Unmount only happens if:
    	 *  (1) the mark is already set (the mark is cleared by mntput())
    	 *  (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
    	 */
    	if (flags & MNT_EXPIRE) {
    		if (mnt == current->fs->rootmnt ||
    		    flags & (MNT_FORCE | MNT_DETACH))
    			return -EINVAL;
    
    		if (atomic_read(&mnt->mnt_count) != 2)
    			return -EBUSY;
    
    		if (!xchg(&mnt->mnt_expiry_mark, 1))
    			return -EAGAIN;
    	}
    
    	/*
    	 * If we may have to abort operations to get out of this
    	 * mount, and they will themselves hold resources we must
    	 * allow the fs to do things. In the Unix tradition of
    	 * 'Gee thats tricky lets do it in userspace' the umount_begin
    	 * might fail to complete on the first run through as other tasks
    	 * must return, and the like. Thats for the mount program to worry
    	 * about for the moment.
    	 */
    
    	lock_kernel();
    	if( (flags&MNT_FORCE) && sb->s_op->umount_begin)
    		sb->s_op->umount_begin(sb);
    	unlock_kernel();
    
    	/*
    	 * No sense to grab the lock for this test, but test itself looks
    	 * somewhat bogus. Suggestions for better replacement?
    	 * Ho-hum... In principle, we might treat that as umount + switch
    	 * to rootfs. GC would eventually take care of the old vfsmount.
    	 * Actually it makes sense, especially if rootfs would contain a
    	 * /reboot - static binary that would close all descriptors and
    	 * call reboot(9). Then init(8) could umount root and exec /reboot.
    	 */
    	if (mnt == current->fs->rootmnt && !(flags & MNT_DETACH)) {
    		/*
    		 * Special case for "unmounting" root ...
    		 * we just try to remount it readonly.
    		 */
    		down_write(&sb->s_umount);
    		if (!(sb->s_flags & MS_RDONLY)) {
    			lock_kernel();
    			DQUOT_OFF(sb);
    			retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
    			unlock_kernel();
    		}
    		up_write(&sb->s_umount);
    		return retval;
    	}
    
    	down_write(&current->namespace->sem);
    	spin_lock(&vfsmount_lock);
    
    	retval = -EBUSY;
    	if (atomic_read(&mnt->mnt_count) == 2 || flags & MNT_DETACH) {
    		if (!list_empty(&mnt->mnt_list))
    			umount_tree(mnt);
    		retval = 0;
    	}
    	spin_unlock(&vfsmount_lock);
    	if (retval)
    		security_sb_umount_busy(mnt);
    	up_write(&current->namespace->sem);
    	return retval;
    }
    
    /*
     * Now umount can handle mount points as well as block devices.
     * This is important for filesystems which use unnamed block devices.
     *
     * We now support a flag for forced unmount like the other 'big iron'
     * unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
     */
    
    asmlinkage long sys_umount(char __user * name, int flags)
    {
    	struct nameidata nd;
    	int retval;
    
    	retval = __user_walk(name, LOOKUP_FOLLOW, &nd);
    	if (retval)
    		goto out;
    	retval = -EINVAL;
    	if (nd.dentry != nd.mnt->mnt_root)
    		goto dput_and_out;
    	if (!check_mnt(nd.mnt))
    		goto dput_and_out;
    
    	retval = -EPERM;
    	if (!capable(CAP_SYS_ADMIN))
    		goto dput_and_out;
    
    	retval = do_umount(nd.mnt, flags);
    dput_and_out:
    	path_release_on_umount(&nd);
    out:
    	return retval;
    }
    
    #ifdef __ARCH_WANT_SYS_OLDUMOUNT
    
    /*
     *	The 2.0 compatible umount. No flags. 
     */
     
    asmlinkage long sys_oldumount(char __user * name)
    {
    	return sys_umount(name,0);
    }
    
    #endif
    
    static int mount_is_safe(struct nameidata *nd)
    {
    	if (capable(CAP_SYS_ADMIN))
    		return 0;
    	return -EPERM;
    #ifdef notyet
    	if (S_ISLNK(nd->dentry->d_inode->i_mode))
    		return -EPERM;
    	if (nd->dentry->d_inode->i_mode & S_ISVTX) {
    		if (current->uid != nd->dentry->d_inode->i_uid)
    			return -EPERM;
    	}
    	if (permission(nd->dentry->d_inode, MAY_WRITE, nd))
    		return -EPERM;
    	return 0;
    #endif
    }
    
    static int
    lives_below_in_same_fs(struct dentry *d, struct dentry *dentry)
    {
    	while (1) {
    		if (d == dentry)
    			return 1;
    		if (d == NULL || d == d->d_parent)
    			return 0;
    		d = d->d_parent;
    	}
    }
    
    static struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry)
    {
    	struct vfsmount *res, *p, *q, *r, *s;
    	struct nameidata nd;
    
    	res = q = clone_mnt(mnt, dentry);
    	if (!q)
    		goto Enomem;
    	q->mnt_mountpoint = mnt->mnt_mountpoint;
    
    	p = mnt;
    	list_for_each_entry(r, &mnt->mnt_mounts, mnt_child) {
    		if (!lives_below_in_same_fs(r->mnt_mountpoint, dentry))
    			continue;
    
    		for (s = r; s; s = next_mnt(s, r)) {
    			while (p != s->mnt_parent) {
    				p = p->mnt_parent;
    				q = q->mnt_parent;
    			}
    			p = s;
    			nd.mnt = q;
    			nd.dentry = p->mnt_mountpoint;
    			q = clone_mnt(p, p->mnt_root);
    			if (!q)
    				goto Enomem;
    			spin_lock(&vfsmount_lock);
    			list_add_tail(&q->mnt_list, &res->mnt_list);
    			attach_mnt(q, &nd);
    			spin_unlock(&vfsmount_lock);
    		}
    	}
    	return res;
     Enomem:
    	if (res) {
    		spin_lock(&vfsmount_lock);
    		umount_tree(res);
    		spin_unlock(&vfsmount_lock);
    	}
    	return NULL;
    }
    
    static int graft_tree(struct vfsmount *mnt, struct nameidata *nd)
    {
    	int err;
    	if (mnt->mnt_sb->s_flags & MS_NOUSER)
    		return -EINVAL;
    
    	if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
    	      S_ISDIR(mnt->mnt_root->d_inode->i_mode))
    		return -ENOTDIR;
    
    	err = -ENOENT;
    	down(&nd->dentry->d_inode->i_sem);
    	if (IS_DEADDIR(nd->dentry->d_inode))
    		goto out_unlock;
    
    	err = security_sb_check_sb(mnt, nd);
    	if (err)
    		goto out_unlock;
    
    	err = -ENOENT;
    	spin_lock(&vfsmount_lock);
    	if (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry)) {
    		struct list_head head;
    
    		attach_mnt(mnt, nd);
    		list_add_tail(&head, &mnt->mnt_list);
    		list_splice(&head, current->namespace->list.prev);
    		mntget(mnt);
    		err = 0;
    	}
    	spin_unlock(&vfsmount_lock);
    out_unlock:
    	up(&nd->dentry->d_inode->i_sem);
    	if (!err)
    		security_sb_post_addmount(mnt, nd);
    	return err;
    }
    
    /*
     * do loopback mount.
     */
    static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
    {
    	struct nameidata old_nd;
    	struct vfsmount *mnt = NULL;
    	int err = mount_is_safe(nd);
    	if (err)
    		return err;
    	if (!old_name || !*old_name)
    		return -EINVAL;
    	err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);
    	if (err)
    		return err;
    
    	down_write(&current->namespace->sem);
    	err = -EINVAL;
    	if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
    		goto out;
    
    	err = -ENOMEM;
    	if (recurse)
    		mnt = copy_tree(old_nd.mnt, old_nd.dentry);
    	else
    		mnt = clone_mnt(old_nd.mnt, old_nd.dentry);
    
    	if (!mnt)
    		goto out;
    
    	/* stop bind mounts from expiring */
    	spin_lock(&vfsmount_lock);
    	list_del_init(&mnt->mnt_expire);
    	spin_unlock(&vfsmount_lock);
    
    	err = graft_tree(mnt, nd);
    	if (err) {
    		spin_lock(&vfsmount_lock);
    		umount_tree(mnt);
    		spin_unlock(&vfsmount_lock);
    	} else
    		mntput(mnt);
    
    out:
    	up_write(&current->namespace->sem);
    	path_release(&old_nd);
    	return err;
    }
    
    /*
     * change filesystem flags. dir should be a physical root of filesystem.
     * If you've mounted a non-root directory somewhere and want to do remount
     * on it - tough luck.
     */
    
    static int do_remount(struct nameidata *nd, int flags, int mnt_flags,
    		      void *data)
    {
    	int err;
    	struct super_block * sb = nd->mnt->mnt_sb;
    
    	if (!capable(CAP_SYS_ADMIN))
    		return -EPERM;
    
    	if (!check_mnt(nd->mnt))
    		return -EINVAL;
    
    	if (nd->dentry != nd->mnt->mnt_root)
    		return -EINVAL;
    
    	down_write(&sb->s_umount);
    	err = do_remount_sb(sb, flags, data, 0);
    	if (!err)
    		nd->mnt->mnt_flags=mnt_flags;
    	up_write(&sb->s_umount);
    	if (!err)
    		security_sb_post_remount(nd->mnt, flags, data);
    	return err;
    }
    
    static int do_move_mount(struct nameidata *nd, char *old_name)
    {
    	struct nameidata old_nd, parent_nd;
    	struct vfsmount *p;
    	int err = 0;
    	if (!capable(CAP_SYS_ADMIN))
    		return -EPERM;
    	if (!old_name || !*old_name)
    		return -EINVAL;
    	err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);
    	if (err)
    		return err;
    
    	down_write(&current->namespace->sem);
    	while(d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
    		;
    	err = -EINVAL;
    	if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
    		goto out;
    
    	err = -ENOENT;
    	down(&nd->dentry->d_inode->i_sem);
    	if (IS_DEADDIR(nd->dentry->d_inode))
    		goto out1;
    
    	spin_lock(&vfsmount_lock);
    	if (!IS_ROOT(nd->dentry) && d_unhashed(nd->dentry))
    		goto out2;
    
    	err = -EINVAL;
    	if (old_nd.dentry != old_nd.mnt->mnt_root)
    		goto out2;
    
    	if (old_nd.mnt == old_nd.mnt->mnt_parent)
    		goto out2;
    
    	if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
    	      S_ISDIR(old_nd.dentry->d_inode->i_mode))
    		goto out2;
    
    	err = -ELOOP;
    	for (p = nd->mnt; p->mnt_parent!=p; p = p->mnt_parent)
    		if (p == old_nd.mnt)
    			goto out2;
    	err = 0;
    
    	detach_mnt(old_nd.mnt, &parent_nd);
    	attach_mnt(old_nd.mnt, nd);
    
    	/* if the mount is moved, it should no longer be expire
    	 * automatically */
    	list_del_init(&old_nd.mnt->mnt_expire);
    out2:
    	spin_unlock(&vfsmount_lock);
    out1:
    	up(&nd->dentry->d_inode->i_sem);
    out:
    	up_write(&current->namespace->sem);
    	if (!err)
    		path_release(&parent_nd);
    	path_release(&old_nd);
    	return err;
    }
    
    /*
     * create a new mount for userspace and request it to be added into the
     * namespace's tree
     */
    static int do_new_mount(struct nameidata *nd, char *type, int flags,
    			int mnt_flags, char *name, void *data)
    {
    	struct vfsmount *mnt;
    
    	if (!type || !memchr(type, 0, PAGE_SIZE))
    		return -EINVAL;
    
    	/* we need capabilities... */
    	if (!capable(CAP_SYS_ADMIN))
    		return -EPERM;
    
    	mnt = do_kern_mount(type, flags, name, data);
    	if (IS_ERR(mnt))
    		return PTR_ERR(mnt);
    
    	return do_add_mount(mnt, nd, mnt_flags, NULL);
    }
    
    /*
     * add a mount into a namespace's mount tree
     * - provide the option of adding the new mount to an expiration list
     */
    int do_add_mount(struct vfsmount *newmnt, struct nameidata *nd,
    		 int mnt_flags, struct list_head *fslist)
    {
    	int err;
    
    	down_write(&current->namespace->sem);
    	/* Something was mounted here while we slept */
    	while(d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
    		;
    	err = -EINVAL;
    	if (!check_mnt(nd->mnt))
    		goto unlock;
    
    	/* Refuse the same filesystem on the same mount point */
    	err = -EBUSY;
    	if (nd->mnt->mnt_sb == newmnt->mnt_sb &&
    	    nd->mnt->mnt_root == nd->dentry)
    		goto unlock;
    
    	err = -EINVAL;
    	if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
    		goto unlock;
    
    	newmnt->mnt_flags = mnt_flags;
    	newmnt->mnt_namespace = current->namespace;
    	err = graft_tree(newmnt, nd);
    
    	if (err == 0 && fslist) {
    		/* add to the specified expiration list */
    		spin_lock(&vfsmount_lock);
    		list_add_tail(&newmnt->mnt_expire, fslist);
    		spin_unlock(&vfsmount_lock);
    	}
    
    unlock:
    	up_write(&current->namespace->sem);
    	mntput(newmnt);
    	return err;
    }
    
    EXPORT_SYMBOL_GPL(do_add_mount);
    
    static void expire_mount(struct vfsmount *mnt, struct list_head *mounts)
    {
    	spin_lock(&vfsmount_lock);
    
    	/*
    	 * Check if mount is still attached, if not, let whoever holds it deal
    	 * with the sucker
    	 */
    	if (mnt->mnt_parent == mnt) {
    		spin_unlock(&vfsmount_lock);
    		return;
    	}
    
    	/*
    	 * Check that it is still dead: the count should now be 2 - as
    	 * contributed by the vfsmount parent and the mntget above
    	 */
    	if (atomic_read(&mnt->mnt_count) == 2) {
    		struct nameidata old_nd;
    
    		/* delete from the namespace */
    		list_del_init(&mnt->mnt_list);
    		mnt->mnt_namespace = NULL;
    		detach_mnt(mnt, &old_nd);
    		spin_unlock(&vfsmount_lock);
    		path_release(&old_nd);
    		mntput(mnt);
    	} else {
    		/*
    		 * Someone brought it back to life whilst we didn't have any
    		 * locks held so return it to the expiration list
    		 */
    		list_add_tail(&mnt->mnt_expire, mounts);
    		spin_unlock(&vfsmount_lock);
    	}
    }
    
    /*
     * process a list of expirable mountpoints with the intent of discarding any
     * mountpoints that aren't in use and haven't been touched since last we came
     * here
     */
    void mark_mounts_for_expiry(struct list_head *mounts)
    {
    	struct namespace *namespace;
    	struct vfsmount *mnt, *next;
    	LIST_HEAD(graveyard);
    
    	if (list_empty(mounts))
    		return;
    
    	spin_lock(&vfsmount_lock);
    
    	/* extract from the expiration list every vfsmount that matches the
    	 * following criteria:
    	 * - only referenced by its parent vfsmount
    	 * - still marked for expiry (marked on the last call here; marks are
    	 *   cleared by mntput())
    	 */
    	list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
    		if (!xchg(&mnt->mnt_expiry_mark, 1) ||
    		    atomic_read(&mnt->mnt_count) != 1)
    			continue;
    
    		mntget(mnt);
    		list_move(&mnt->mnt_expire, &graveyard);
    	}
    
    	/*
    	 * go through the vfsmounts we've just consigned to the graveyard to
    	 * - check that they're still dead
    	 * - delete the vfsmount from the appropriate namespace under lock
    	 * - dispose of the corpse
    	 */
    	while (!list_empty(&graveyard)) {
    		mnt = list_entry(graveyard.next, struct vfsmount, mnt_expire);
    		list_del_init(&mnt->mnt_expire);
    
    		/* don't do anything if the namespace is dead - all the
    		 * vfsmounts from it are going away anyway */
    		namespace = mnt->mnt_namespace;
    		if (!namespace || !namespace->root)
    			continue;
    		get_namespace(namespace);
    
    		spin_unlock(&vfsmount_lock);
    		down_write(&namespace->sem);
    		expire_mount(mnt, mounts);
    		up_write(&namespace->sem);
    
    		mntput(mnt);
    		put_namespace(namespace);
    
    		spin_lock(&vfsmount_lock);
    	}
    
    	spin_unlock(&vfsmount_lock);
    }
    
    EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
    
    /*
     * Some copy_from_user() implementations do not return the exact number of
     * bytes remaining to copy on a fault.  But copy_mount_options() requires that.
     * Note that this function differs from copy_from_user() in that it will oops
     * on bad values of `to', rather than returning a short copy.
     */
    static long
    exact_copy_from_user(void *to, const void __user *from, unsigned long n)
    {
    	char *t = to;
    	const char __user *f = from;
    	char c;
    
    	if (!access_ok(VERIFY_READ, from, n))
    		return n;
    
    	while (n) {
    		if (__get_user(c, f)) {
    			memset(t, 0, n);
    			break;
    		}
    		*t++ = c;
    		f++;
    		n--;
    	}
    	return n;
    }
    
    int copy_mount_options(const void __user *data, unsigned long *where)
    {
    	int i;
    	unsigned long page;
    	unsigned long size;
    	
    	*where = 0;
    	if (!data)
    		return 0;
    
    	if (!(page = __get_free_page(GFP_KERNEL)))
    		return -ENOMEM;
    
    	/* We only care that *some* data at the address the user
    	 * gave us is valid.  Just in case, we'll zero
    	 * the remainder of the page.
    	 */
    	/* copy_from_user cannot cross TASK_SIZE ! */
    	size = TASK_SIZE - (unsigned long)data;
    	if (size > PAGE_SIZE)
    		size = PAGE_SIZE;
    
    	i = size - exact_copy_from_user((void *)page, data, size);
    	if (!i) {
    		free_page(page); 
    		return -EFAULT;
    	}
    	if (i != PAGE_SIZE)
    		memset((char *)page + i, 0, PAGE_SIZE - i);
    	*where = page;
    	return 0;
    }
    
    /*
     * Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
     * be given to the mount() call (ie: read-only, no-dev, no-suid etc).
     *
     * data is a (void *) that can point to any structure up to
     * PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
     * information (or be NULL).
     *
     * Pre-0.97 versions of mount() didn't have a flags word.
     * When the flags word was introduced its top half was required
     * to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
     * Therefore, if this magic number is present, it carries no information
     * and must be discarded.
     */
    long do_mount(char * dev_name, char * dir_name, char *type_page,
    		  unsigned long flags, void *data_page)
    {
    	struct nameidata nd;
    	int retval = 0;
    	int mnt_flags = 0;
    
    	/* Discard magic */
    	if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
    		flags &= ~MS_MGC_MSK;
    
    	/* Basic sanity checks */
    
    	if (!dir_name || !*dir_name || !memchr(dir_name, 0, PAGE_SIZE))
    		return -EINVAL;
    	if (dev_name && !memchr(dev_name, 0, PAGE_SIZE))
    		return -EINVAL;
    
    	if (data_page)
    		((char *)data_page)[PAGE_SIZE - 1] = 0;
    
    	/* Separate the per-mountpoint flags */
    	if (flags & MS_NOSUID)
    		mnt_flags |= MNT_NOSUID;
    	if (flags & MS_NODEV)
    		mnt_flags |= MNT_NODEV;
    	if (flags & MS_NOEXEC)
    		mnt_flags |= MNT_NOEXEC;
    	flags &= ~(MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_ACTIVE);
    
    	/* ... and get the mountpoint */
    	retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd);
    	if (retval)
    		return retval;
    
    	retval = security_sb_mount(dev_name, &nd, type_page, flags, data_page);
    	if (retval)
    		goto dput_out;
    
    	if (flags & MS_REMOUNT)
    		retval = do_remount(&nd, flags & ~MS_REMOUNT, mnt_flags,
    				    data_page);
    	else if (flags & MS_BIND)
    		retval = do_loopback(&nd, dev_name, flags & MS_REC);
    	else if (flags & MS_MOVE)
    		retval = do_move_mount(&nd, dev_name);
    	else
    		retval = do_new_mount(&nd, type_page, flags, mnt_flags,
    				      dev_name, data_page);
    dput_out:
    	path_release(&nd);
    	return retval;
    }
    
    int copy_namespace(int flags, struct task_struct *tsk)
    {
    	struct namespace *namespace = tsk->namespace;
    	struct namespace *new_ns;
    	struct vfsmount *rootmnt = NULL, *pwdmnt = NULL, *altrootmnt = NULL;
    	struct fs_struct *fs = tsk->fs;
    	struct vfsmount *p, *q;
    
    	if (!namespace)
    		return 0;
    
    	get_namespace(namespace);
    
    	if (!(flags & CLONE_NEWNS))
    		return 0;
    
    	if (!capable(CAP_SYS_ADMIN)) {
    		put_namespace(namespace);
    		return -EPERM;
    	}
    
    	new_ns = kmalloc(sizeof(struct namespace), GFP_KERNEL);
    	if (!new_ns)
    		goto out;
    
    	atomic_set(&new_ns->count, 1);
    	init_rwsem(&new_ns->sem);
    	INIT_LIST_HEAD(&new_ns->list);
    
    	down_write(&tsk->namespace->sem);
    	/* First pass: copy the tree topology */
    	new_ns->root = copy_tree(namespace->root, namespace->root->mnt_root);
    	if (!new_ns->root) {
    		up_write(&tsk->namespace->sem);
    		kfree(new_ns);
    		goto out;
    	}
    	spin_lock(&vfsmount_lock);
    	list_add_tail(&new_ns->list, &new_ns->root->mnt_list);
    	spin_unlock(&vfsmount_lock);
    
    	/*
    	 * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
    	 * as belonging to new namespace.  We have already acquired a private
    	 * fs_struct, so tsk->fs->lock is not needed.
    	 */
    	p = namespace->root;
    	q = new_ns->root;
    	while (p) {
    		q->mnt_namespace = new_ns;
    		if (fs) {
    			if (p == fs->rootmnt) {
    				rootmnt = p;
    				fs->rootmnt = mntget(q);
    			}
    			if (p == fs->pwdmnt) {
    				pwdmnt = p;
    				fs->pwdmnt = mntget(q);
    			}
    			if (p == fs->altrootmnt) {
    				altrootmnt = p;
    				fs->altrootmnt = mntget(q);
    			}
    		}
    		p = next_mnt(p, namespace->root);
    		q = next_mnt(q, new_ns->root);
    	}
    	up_write(&tsk->namespace->sem);
    
    	tsk->namespace = new_ns;
    
    	if (rootmnt)
    		mntput(rootmnt);
    	if (pwdmnt)
    		mntput(pwdmnt);
    	if (altrootmnt)
    		mntput(altrootmnt);
    
    	put_namespace(namespace);
    	return 0;
    
    out:
    	put_namespace(namespace);
    	return -ENOMEM;
    }
    
    asmlinkage long sys_mount(char __user * dev_name, char __user * dir_name,
    			  char __user * type, unsigned long flags,
    			  void __user * data)
    {
    	int retval;
    	unsigned long data_page;
    	unsigned long type_page;
    	unsigned long dev_page;
    	char *dir_page;
    
    	retval = copy_mount_options (type, &type_page);
    	if (retval < 0)
    		return retval;
    
    	dir_page = getname(dir_name);
    	retval = PTR_ERR(dir_page);
    	if (IS_ERR(dir_page))
    		goto out1;
    
    	retval = copy_mount_options (dev_name, &dev_page);
    	if (retval < 0)
    		goto out2;
    
    	retval = copy_mount_options (data, &data_page);
    	if (retval < 0)
    		goto out3;
    
    	lock_kernel();
    	retval = do_mount((char*)dev_page, dir_page, (char*)type_page,
    			  flags, (void*)data_page);
    	unlock_kernel();
    	free_page(data_page);
    
    out3:
    	free_page(dev_page);
    out2:
    	putname(dir_page);
    out1:
    	free_page(type_page);
    	return retval;
    }
    
    /*
     * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
     * It can block. Requires the big lock held.
     */
    void set_fs_root(struct fs_struct *fs, struct vfsmount *mnt,
    		 struct dentry *dentry)
    {
    	struct dentry *old_root;
    	struct vfsmount *old_rootmnt;
    	write_lock(&fs->lock);
    	old_root = fs->root;
    	old_rootmnt = fs->rootmnt;
    	fs->rootmnt = mntget(mnt);
    	fs->root = dget(dentry);
    	write_unlock(&fs->lock);
    	if (old_root) {
    		dput(old_root);
    		mntput(old_rootmnt);
    	}
    }
    
    /*
     * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
     * It can block. Requires the big lock held.
     */
    void set_fs_pwd(struct fs_struct *fs, struct vfsmount *mnt,
    		struct dentry *dentry)
    {
    	struct dentry *old_pwd;
    	struct vfsmount *old_pwdmnt;
    
    	write_lock(&fs->lock);
    	old_pwd = fs->pwd;
    	old_pwdmnt = fs->pwdmnt;
    	fs->pwdmnt = mntget(mnt);
    	fs->pwd = dget(dentry);
    	write_unlock(&fs->lock);
    
    	if (old_pwd) {
    		dput(old_pwd);
    		mntput(old_pwdmnt);
    	}
    }
    
    static void chroot_fs_refs(struct nameidata *old_nd, struct nameidata *new_nd)
    {
    	struct task_struct *g, *p;
    	struct fs_struct *fs;
    
    	read_lock(&tasklist_lock);
    	do_each_thread(g, p) {
    		task_lock(p);
    		fs = p->fs;
    		if (fs) {
    			atomic_inc(&fs->count);
    			task_unlock(p);
    			if (fs->root==old_nd->dentry&&fs->rootmnt==old_nd->mnt)
    				set_fs_root(fs, new_nd->mnt, new_nd->dentry);
    			if (fs->pwd==old_nd->dentry&&fs->pwdmnt==old_nd->mnt)
    				set_fs_pwd(fs, new_nd->mnt, new_nd->dentry);
    			put_fs_struct(fs);
    		} else
    			task_unlock(p);
    	} while_each_thread(g, p);
    	read_unlock(&tasklist_lock);
    }
    
    /*
     * pivot_root Semantics:
     * Moves the root file system of the current process to the directory put_old,
     * makes new_root as the new root file system of the current process, and sets
     * root/cwd of all processes which had them on the current root to new_root.
     *
     * Restrictions:
     * The new_root and put_old must be directories, and  must not be on the
     * same file  system as the current process root. The put_old  must  be
     * underneath new_root,  i.e. adding a non-zero number of /.. to the string
     * pointed to by put_old must yield the same directory as new_root. No other
     * file system may be mounted on put_old. After all, new_root is a mountpoint.
     *
     * Notes:
     *  - we don't move root/cwd if they are not at the root (reason: if something
     *    cared enough to change them, it's probably wrong to force them elsewhere)
     *  - it's okay to pick a root that isn't the root of a file system, e.g.
     *    /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
     *    though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
     *    first.
     */
    
    asmlinkage long sys_pivot_root(const char __user *new_root, const char __user *put_old)
    {
    	struct vfsmount *tmp;
    	struct nameidata new_nd, old_nd, parent_nd, root_parent, user_nd;
    	int error;
    
    	if (!capable(CAP_SYS_ADMIN))
    		return -EPERM;
    
    	lock_kernel();
    
    	error = __user_walk(new_root, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, &new_nd);
    	if (error)
    		goto out0;
    	error = -EINVAL;
    	if (!check_mnt(new_nd.mnt))
    		goto out1;
    
    	error = __user_walk(put_old, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, &old_nd);
    	if (error)
    		goto out1;
    
    	error = security_sb_pivotroot(&old_nd, &new_nd);
    	if (error) {
    		path_release(&old_nd);
    		goto out1;
    	}
    
    	read_lock(&current->fs->lock);
    	user_nd.mnt = mntget(current->fs->rootmnt);
    	user_nd.dentry = dget(current->fs->root);
    	read_unlock(&current->fs->lock);
    	down_write(&current->namespace->sem);
    	down(&old_nd.dentry->d_inode->i_sem);
    	error = -EINVAL;
    	if (!check_mnt(user_nd.mnt))
    		goto out2;
    	error = -ENOENT;
    	if (IS_DEADDIR(new_nd.dentry->d_inode))
    		goto out2;
    	if (d_unhashed(new_nd.dentry) && !IS_ROOT(new_nd.dentry))
    		goto out2;
    	if (d_unhashed(old_nd.dentry) && !IS_ROOT(old_nd.dentry))
    		goto out2;
    	error = -EBUSY;
    	if (new_nd.mnt == user_nd.mnt || old_nd.mnt == user_nd.mnt)
    		goto out2; /* loop, on the same file system  */
    	error = -EINVAL;
    	if (user_nd.mnt->mnt_root != user_nd.dentry)
    		goto out2; /* not a mountpoint */
    	if (user_nd.mnt->mnt_parent == user_nd.mnt)
    		goto out2; /* not attached */
    	if (new_nd.mnt->mnt_root != new_nd.dentry)
    		goto out2; /* not a mountpoint */
    	if (new_nd.mnt->mnt_parent == new_nd.mnt)
    		goto out2; /* not attached */
    	tmp = old_nd.mnt; /* make sure we can reach put_old from new_root */
    	spin_lock(&vfsmount_lock);
    	if (tmp != new_nd.mnt) {
    		for (;;) {
    			if (tmp->mnt_parent == tmp)
    				goto out3; /* already mounted on put_old */
    			if (tmp->mnt_parent == new_nd.mnt)
    				break;
    			tmp = tmp->mnt_parent;
    		}
    		if (!is_subdir(tmp->mnt_mountpoint, new_nd.dentry))
    			goto out3;
    	} else if (!is_subdir(old_nd.dentry, new_nd.dentry))
    		goto out3;
    	detach_mnt(new_nd.mnt, &parent_nd);
    	detach_mnt(user_nd.mnt, &root_parent);
    	attach_mnt(user_nd.mnt, &old_nd);     /* mount old root on put_old */
    	attach_mnt(new_nd.mnt, &root_parent); /* mount new_root on / */
    	spin_unlock(&vfsmount_lock);
    	chroot_fs_refs(&user_nd, &new_nd);
    	security_sb_post_pivotroot(&user_nd, &new_nd);
    	error = 0;
    	path_release(&root_parent);
    	path_release(&parent_nd);
    out2:
    	up(&old_nd.dentry->d_inode->i_sem);
    	up_write(&current->namespace->sem);
    	path_release(&user_nd);
    	path_release(&old_nd);
    out1:
    	path_release(&new_nd);
    out0:
    	unlock_kernel();
    	return error;
    out3:
    	spin_unlock(&vfsmount_lock);
    	goto out2;
    }
    
    static void __init init_mount_tree(void)
    {
    	struct vfsmount *mnt;
    	struct namespace *namespace;
    	struct task_struct *g, *p;
    
    	mnt = do_kern_mount("rootfs", 0, "rootfs", NULL);
    	if (IS_ERR(mnt))
    		panic("Can't create rootfs");
    	namespace = kmalloc(sizeof(*namespace), GFP_KERNEL);
    	if (!namespace)
    		panic("Can't allocate initial namespace");
    	atomic_set(&namespace->count, 1);
    	INIT_LIST_HEAD(&namespace->list);
    	init_rwsem(&namespace->sem);
    	list_add(&mnt->mnt_list, &namespace->list);
    	namespace->root = mnt;
    	mnt->mnt_namespace = namespace;
    
    	init_task.namespace = namespace;
    	read_lock(&tasklist_lock);
    	do_each_thread(g, p) {
    		get_namespace(namespace);
    		p->namespace = namespace;
    	} while_each_thread(g, p);
    	read_unlock(&tasklist_lock);
    
    	set_fs_pwd(current->fs, namespace->root, namespace->root->mnt_root);
    	set_fs_root(current->fs, namespace->root, namespace->root->mnt_root);
    }
    
    void __init mnt_init(unsigned long mempages)
    {
    	struct list_head *d;
    	unsigned int nr_hash;
    	int i;
    
    	mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct vfsmount),
    			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
    
    	mount_hashtable = (struct list_head *)
    		__get_free_page(GFP_ATOMIC);
    
    	if (!mount_hashtable)
    		panic("Failed to allocate mount hash table\n");
    
    	/*
    	 * Find the power-of-two list-heads that can fit into the allocation..
    	 * We don't guarantee that "sizeof(struct list_head)" is necessarily
    	 * a power-of-two.
    	 */
    	nr_hash = PAGE_SIZE / sizeof(struct list_head);
    	hash_bits = 0;
    	do {
    		hash_bits++;
    	} while ((nr_hash >> hash_bits) != 0);
    	hash_bits--;
    
    	/*
    	 * Re-calculate the actual number of entries and the mask
    	 * from the number of bits we can fit.
    	 */
    	nr_hash = 1UL << hash_bits;
    	hash_mask = nr_hash-1;
    
    	printk("Mount-cache hash table entries: %d\n", nr_hash);
    
    	/* And initialize the newly allocated array */
    	d = mount_hashtable;
    	i = nr_hash;
    	do {
    		INIT_LIST_HEAD(d);
    		d++;
    		i--;
    	} while (i);
    	sysfs_init();
    	init_rootfs();
    	init_mount_tree();
    }
    
    void __put_namespace(struct namespace *namespace)
    {
    	struct vfsmount *root = namespace->root;
    	namespace->root = NULL;
    	spin_unlock(&vfsmount_lock);
    	down_write(&namespace->sem);
    	spin_lock(&vfsmount_lock);
    	umount_tree(root);
    	spin_unlock(&vfsmount_lock);
    	up_write(&namespace->sem);
    	kfree(namespace);
    }