/*
   *  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/syscalls.h>
  #include <linux/slab.h>
  #include <linux/sched.h>
  #include <linux/smp_lock.h>
  #include <linux/init.h>

  #include <linux/kernel.h>

  #include <linux/quotaops.h>
  #include <linux/acct.h>

  #include <linux/capability.h>

  #include <linux/module.h>

  #include <linux/sysfs.h>

  #include <linux/seq_file.h>

  #include <linux/mnt_namespace.h>

  #include <linux/namei.h>
  #include <linux/security.h>
  #include <linux/mount.h>

  #include <linux/ramfs.h>

  #include <asm/uaccess.h>
  #include <asm/unistd.h>

  #include "pnode.h"

  #include "internal.h"

  /* spinlock for vfsmount related operations, inplace of dcache_lock */

  __cacheline_aligned_in_smp DEFINE_SPINLOCK(vfsmount_lock);
  
  static int event;

  static struct list_head *mount_hashtable __read_mostly;

  static int hash_mask __read_mostly, hash_bits __read_mostly;

  static struct kmem_cache *mnt_cache __read_mostly;

  static struct rw_semaphore namespace_sem;

  /* /sys/fs */
  decl_subsys(fs, NULL, NULL);
  EXPORT_SYMBOL_GPL(fs_subsys);

  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_zalloc(mnt_cache, GFP_KERNEL);

  	if (mnt) {

  		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);

  		INIT_LIST_HEAD(&mnt->mnt_share);

  		INIT_LIST_HEAD(&mnt->mnt_slave_list);
  		INIT_LIST_HEAD(&mnt->mnt_slave);

  		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;
  }

  int simple_set_mnt(struct vfsmount *mnt, struct super_block *sb)
  {
  	mnt->mnt_sb = sb;
  	mnt->mnt_root = dget(sb->s_root);
  	return 0;
  }
  
  EXPORT_SYMBOL(simple_set_mnt);

  void free_vfsmnt(struct vfsmount *mnt)
  {
  	kfree(mnt->mnt_devname);
  	kmem_cache_free(mnt_cache, mnt);
  }
  
  /*

   * find the first or last mount at @dentry on vfsmount @mnt depending on
   * @dir. If @dir is set return the first mount else return the last mount.

   */

  struct vfsmount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry,
  			      int dir)

  {

  	struct list_head *head = mount_hashtable + hash(mnt, dentry);
  	struct list_head *tmp = head;

  	struct vfsmount *p, *found = NULL;

  	for (;;) {

  		tmp = dir ? tmp->next : tmp->prev;

  		p = NULL;
  		if (tmp == head)
  			break;
  		p = list_entry(tmp, struct vfsmount, mnt_hash);
  		if (p->mnt_parent == mnt && p->mnt_mountpoint == dentry) {

  			found = p;

  			break;
  		}
  	}

  	return found;
  }

  /*
   * lookup_mnt increments the ref count before returning
   * the vfsmount struct.
   */
  struct vfsmount *lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
  {
  	struct vfsmount *child_mnt;
  	spin_lock(&vfsmount_lock);
  	if ((child_mnt = __lookup_mnt(mnt, dentry, 1)))
  		mntget(child_mnt);
  	spin_unlock(&vfsmount_lock);
  	return child_mnt;
  }

  static inline int check_mnt(struct vfsmount *mnt)
  {

  	return mnt->mnt_ns == current->nsproxy->mnt_ns;

  }

  static void touch_mnt_namespace(struct mnt_namespace *ns)

  {
  	if (ns) {
  		ns->event = ++event;
  		wake_up_interruptible(&ns->poll);
  	}
  }

  static void __touch_mnt_namespace(struct mnt_namespace *ns)

  {
  	if (ns && ns->event != event) {
  		ns->event = event;
  		wake_up_interruptible(&ns->poll);
  	}
  }

  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--;
  }

  void mnt_set_mountpoint(struct vfsmount *mnt, struct dentry *dentry,
  			struct vfsmount *child_mnt)
  {
  	child_mnt->mnt_parent = mntget(mnt);
  	child_mnt->mnt_mountpoint = dget(dentry);
  	dentry->d_mounted++;
  }

  static void attach_mnt(struct vfsmount *mnt, struct nameidata *nd)
  {

  	mnt_set_mountpoint(nd->mnt, nd->dentry, mnt);
  	list_add_tail(&mnt->mnt_hash, mount_hashtable +
  			hash(nd->mnt, nd->dentry));

  	list_add_tail(&mnt->mnt_child, &nd->mnt->mnt_mounts);

  }
  
  /*
   * the caller must hold vfsmount_lock
   */
  static void commit_tree(struct vfsmount *mnt)
  {
  	struct vfsmount *parent = mnt->mnt_parent;
  	struct vfsmount *m;
  	LIST_HEAD(head);

  	struct mnt_namespace *n = parent->mnt_ns;

  
  	BUG_ON(parent == mnt);
  
  	list_add_tail(&head, &mnt->mnt_list);
  	list_for_each_entry(m, &head, mnt_list)

  		m->mnt_ns = n;

  	list_splice(&head, n->list.prev);
  
  	list_add_tail(&mnt->mnt_hash, mount_hashtable +
  				hash(parent, mnt->mnt_mountpoint));
  	list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);

  	touch_mnt_namespace(n);

  }
  
  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 *skip_mnt_tree(struct vfsmount *p)
  {
  	struct list_head *prev = p->mnt_mounts.prev;
  	while (prev != &p->mnt_mounts) {
  		p = list_entry(prev, struct vfsmount, mnt_child);
  		prev = p->mnt_mounts.prev;
  	}
  	return p;
  }

  static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
  					int flag)

  {
  	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;

  		if (flag & CL_SLAVE) {
  			list_add(&mnt->mnt_slave, &old->mnt_slave_list);
  			mnt->mnt_master = old;
  			CLEAR_MNT_SHARED(mnt);
  		} else {
  			if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
  				list_add(&mnt->mnt_share, &old->mnt_share);
  			if (IS_MNT_SLAVE(old))
  				list_add(&mnt->mnt_slave, &old->mnt_slave);
  			mnt->mnt_master = old->mnt_master;
  		}

  		if (flag & CL_MAKE_SHARED)
  			set_mnt_shared(mnt);

  
  		/* stick the duplicate mount on the same expiry list
  		 * as the original if that was on one */

  		if (flag & CL_EXPIRE) {
  			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 mnt_namespace *n = m->private;

  	down_read(&namespace_sem);

  	return seq_list_start(&n->list, *pos);

  }
  
  static void *m_next(struct seq_file *m, void *v, loff_t *pos)
  {

  	struct mnt_namespace *n = m->private;

  
  	return seq_list_next(v, &n->list, pos);

  }
  
  static void m_stop(struct seq_file *m, void *v)
  {

  	up_read(&namespace_sem);

  }
  
  static inline void mangle(struct seq_file *m, const char *s)
  {
  	seq_escape(m, s, " \t
  \\");
  }
  
  static int show_vfsmnt(struct seq_file *m, void *v)
  {

  	struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);

  	int err = 0;
  	static struct proc_fs_info {
  		int flag;
  		char *str;
  	} fs_info[] = {
  		{ MS_SYNCHRONOUS, ",sync" },
  		{ MS_DIRSYNC, ",dirsync" },
  		{ MS_MANDLOCK, ",mand" },

  		{ 0, NULL }
  	};
  	static struct proc_fs_info mnt_info[] = {
  		{ MNT_NOSUID, ",nosuid" },
  		{ MNT_NODEV, ",nodev" },
  		{ MNT_NOEXEC, ",noexec" },

  		{ MNT_NOATIME, ",noatime" },
  		{ MNT_NODIRATIME, ",nodiratime" },

  		{ MNT_RELATIME, ",relatime" },

  		{ 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
  \\");
  	seq_putc(m, ' ');
  	mangle(m, mnt->mnt_sb->s_type->name);

  	if (mnt->mnt_sb->s_subtype && mnt->mnt_sb->s_subtype[0]) {
  		seq_putc(m, '.');
  		mangle(m, mnt->mnt_sb->s_subtype);
  	}

  	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
  ");
  	return err;
  }
  
  struct seq_operations mounts_op = {
  	.start	= m_start,
  	.next	= m_next,
  	.stop	= m_stop,
  	.show	= show_vfsmnt
  };

  static int show_vfsstat(struct seq_file *m, void *v)
  {

  	struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);

  	int err = 0;
  
  	/* device */
  	if (mnt->mnt_devname) {
  		seq_puts(m, "device ");
  		mangle(m, mnt->mnt_devname);
  	} else
  		seq_puts(m, "no device");
  
  	/* mount point */
  	seq_puts(m, " mounted on ");
  	seq_path(m, mnt, mnt->mnt_root, " \t
  \\");
  	seq_putc(m, ' ');
  
  	/* file system type */
  	seq_puts(m, "with fstype ");
  	mangle(m, mnt->mnt_sb->s_type->name);
  
  	/* optional statistics */
  	if (mnt->mnt_sb->s_op->show_stats) {
  		seq_putc(m, ' ');
  		err = mnt->mnt_sb->s_op->show_stats(m, mnt);
  	}
  
  	seq_putc(m, '
  ');
  	return err;
  }
  
  struct seq_operations mountstats_op = {
  	.start	= m_start,
  	.next	= m_next,
  	.stop	= m_stop,
  	.show	= show_vfsstat,
  };

  /**
   * 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)
  {

  	int actual_refs = 0;
  	int minimum_refs = 0;
  	struct vfsmount *p;

  
  	spin_lock(&vfsmount_lock);

  	for (p = mnt; p; p = next_mnt(p, mnt)) {

  		actual_refs += atomic_read(&p->mnt_count);
  		minimum_refs += 2;

  	}
  	spin_unlock(&vfsmount_lock);
  
  	if (actual_refs > minimum_refs)

  		return 0;

  	return 1;

  }
  
  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)
  {

  	int ret = 1;

  	spin_lock(&vfsmount_lock);
  	if (propagate_mount_busy(mnt, 2))

  		ret = 0;

  	spin_unlock(&vfsmount_lock);
  	return ret;

  }
  
  EXPORT_SYMBOL(may_umount);

  void release_mounts(struct list_head *head)

  {
  	struct vfsmount *mnt;

  	while (!list_empty(head)) {

  		mnt = list_first_entry(head, struct vfsmount, mnt_hash);

  		list_del_init(&mnt->mnt_hash);
  		if (mnt->mnt_parent != mnt) {
  			struct dentry *dentry;
  			struct vfsmount *m;
  			spin_lock(&vfsmount_lock);
  			dentry = mnt->mnt_mountpoint;
  			m = mnt->mnt_parent;
  			mnt->mnt_mountpoint = mnt->mnt_root;
  			mnt->mnt_parent = mnt;
  			spin_unlock(&vfsmount_lock);
  			dput(dentry);
  			mntput(m);
  		}
  		mntput(mnt);
  	}
  }

  void umount_tree(struct vfsmount *mnt, int propagate, struct list_head *kill)

  {
  	struct vfsmount *p;

  	for (p = mnt; p; p = next_mnt(p, mnt))
  		list_move(&p->mnt_hash, kill);

  	if (propagate)
  		propagate_umount(kill);

  	list_for_each_entry(p, kill, mnt_hash) {
  		list_del_init(&p->mnt_expire);
  		list_del_init(&p->mnt_list);

  		__touch_mnt_namespace(p->mnt_ns);
  		p->mnt_ns = NULL;

  		list_del_init(&p->mnt_child);
  		if (p->mnt_parent != p)

  			p->mnt_mountpoint->d_mounted--;

  		change_mnt_propagation(p, MS_PRIVATE);

  	}
  }
  
  static int do_umount(struct vfsmount *mnt, int flags)
  {

  	struct super_block *sb = mnt->mnt_sb;

  	int retval;

  	LIST_HEAD(umount_list);

  
  	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 (sb->s_op->umount_begin)
  		sb->s_op->umount_begin(mnt, flags);

  	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(&namespace_sem);

  	spin_lock(&vfsmount_lock);

  	event++;

  	retval = -EBUSY;

  	if (flags & MNT_DETACH || !propagate_mount_busy(mnt, 2)) {

  		if (!list_empty(&mnt->mnt_list))

  			umount_tree(mnt, 1, &umount_list);

  		retval = 0;
  	}
  	spin_unlock(&vfsmount_lock);
  	if (retval)
  		security_sb_umount_busy(mnt);

  	up_write(&namespace_sem);

  	release_mounts(&umount_list);

  	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 (vfs_permission(nd, MAY_WRITE))

  		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;
  	}
  }

  struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,

  					int flag)

  {
  	struct vfsmount *res, *p, *q, *r, *s;

  	struct nameidata nd;

  	if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
  		return NULL;

  	res = q = clone_mnt(mnt, dentry, flag);

  	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)) {

  			if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(s)) {
  				s = skip_mnt_tree(s);
  				continue;
  			}

  			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, flag);

  			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) {

  		LIST_HEAD(umount_list);

  		spin_lock(&vfsmount_lock);

  		umount_tree(res, 0, &umount_list);

  		spin_unlock(&vfsmount_lock);

  		release_mounts(&umount_list);

  	}
  	return NULL;
  }

  /*
   *  @source_mnt : mount tree to be attached

   *  @nd         : place the mount tree @source_mnt is attached
   *  @parent_nd  : if non-null, detach the source_mnt from its parent and
   *  		   store the parent mount and mountpoint dentry.
   *  		   (done when source_mnt is moved)

   *
   *  NOTE: in the table below explains the semantics when a source mount
   *  of a given type is attached to a destination mount of a given type.

   * ---------------------------------------------------------------------------
   * |         BIND MOUNT OPERATION                                            |
   * |**************************************************************************
   * | source-->| shared        |       private  |       slave    | unbindable |
   * | dest     |               |                |                |            |
   * |   |      |               |                |                |            |
   * |   v      |               |                |                |            |
   * |**************************************************************************
   * |  shared  | shared (++)   |     shared (+) |     shared(+++)|  invalid   |
   * |          |               |                |                |            |
   * |non-shared| shared (+)    |      private   |      slave (*) |  invalid   |
   * ***************************************************************************

   * A bind operation clones the source mount and mounts the clone on the
   * destination mount.
   *
   * (++)  the cloned mount is propagated to all the mounts in the propagation
   * 	 tree of the destination mount and the cloned mount is added to
   * 	 the peer group of the source mount.
   * (+)   the cloned mount is created under the destination mount and is marked
   *       as shared. The cloned mount is added to the peer group of the source
   *       mount.

   * (+++) the mount is propagated to all the mounts in the propagation tree
   *       of the destination mount and the cloned mount is made slave
   *       of the same master as that of the source mount. The cloned mount
   *       is marked as 'shared and slave'.
   * (*)   the cloned mount is made a slave of the same master as that of the
   * 	 source mount.
   *

   * ---------------------------------------------------------------------------
   * |         		MOVE MOUNT OPERATION                                 |
   * |**************************************************************************
   * | source-->| shared        |       private  |       slave    | unbindable |
   * | dest     |               |                |                |            |
   * |   |      |               |                |                |            |
   * |   v      |               |                |                |            |
   * |**************************************************************************
   * |  shared  | shared (+)    |     shared (+) |    shared(+++) |  invalid   |
   * |          |               |                |                |            |
   * |non-shared| shared (+*)   |      private   |    slave (*)   | unbindable |
   * ***************************************************************************

   *
   * (+)  the mount is moved to the destination. And is then propagated to
   * 	all the mounts in the propagation tree of the destination mount.

   * (+*)  the mount is moved to the destination.

   * (+++)  the mount is moved to the destination and is then propagated to
   * 	all the mounts belonging to the destination mount's propagation tree.
   * 	the mount is marked as 'shared and slave'.
   * (*)	the mount continues to be a slave at the new location.

   *
   * if the source mount is a tree, the operations explained above is
   * applied to each mount in the tree.
   * Must be called without spinlocks held, since this function can sleep
   * in allocations.
   */
  static int attach_recursive_mnt(struct vfsmount *source_mnt,

  			struct nameidata *nd, struct nameidata *parent_nd)

  {
  	LIST_HEAD(tree_list);
  	struct vfsmount *dest_mnt = nd->mnt;
  	struct dentry *dest_dentry = nd->dentry;
  	struct vfsmount *child, *p;
  
  	if (propagate_mnt(dest_mnt, dest_dentry, source_mnt, &tree_list))
  		return -EINVAL;
  
  	if (IS_MNT_SHARED(dest_mnt)) {
  		for (p = source_mnt; p; p = next_mnt(p, source_mnt))
  			set_mnt_shared(p);
  	}
  
  	spin_lock(&vfsmount_lock);

  	if (parent_nd) {
  		detach_mnt(source_mnt, parent_nd);
  		attach_mnt(source_mnt, nd);

  		touch_mnt_namespace(current->nsproxy->mnt_ns);

  	} else {
  		mnt_set_mountpoint(dest_mnt, dest_dentry, source_mnt);
  		commit_tree(source_mnt);
  	}

  
  	list_for_each_entry_safe(child, p, &tree_list, mnt_hash) {
  		list_del_init(&child->mnt_hash);
  		commit_tree(child);
  	}
  	spin_unlock(&vfsmount_lock);
  	return 0;
  }

  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;

  	mutex_lock(&nd->dentry->d_inode->i_mutex);

  	if (IS_DEADDIR(nd->dentry->d_inode))
  		goto out_unlock;
  
  	err = security_sb_check_sb(mnt, nd);
  	if (err)
  		goto out_unlock;
  
  	err = -ENOENT;

  	if (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry))

  		err = attach_recursive_mnt(mnt, nd, NULL);

  out_unlock:

  	mutex_unlock(&nd->dentry->d_inode->i_mutex);

  	if (!err)
  		security_sb_post_addmount(mnt, nd);
  	return err;
  }
  
  /*

   * recursively change the type of the mountpoint.
   */
  static int do_change_type(struct nameidata *nd, int flag)
  {
  	struct vfsmount *m, *mnt = nd->mnt;
  	int recurse = flag & MS_REC;
  	int type = flag & ~MS_REC;

  	if (!capable(CAP_SYS_ADMIN))
  		return -EPERM;

  	if (nd->dentry != nd->mnt->mnt_root)
  		return -EINVAL;
  
  	down_write(&namespace_sem);
  	spin_lock(&vfsmount_lock);
  	for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
  		change_mnt_propagation(m, type);
  	spin_unlock(&vfsmount_lock);
  	up_write(&namespace_sem);
  	return 0;
  }
  
  /*

   * 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(&namespace_sem);

  	err = -EINVAL;

  	if (IS_MNT_UNBINDABLE(old_nd.mnt))
   		goto out;

  	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, 0);

  	else

  		mnt = clone_mnt(old_nd.mnt, old_nd.dentry, 0);

  
  	if (!mnt)
  		goto out;

  	err = graft_tree(mnt, nd);
  	if (err) {

  		LIST_HEAD(umount_list);

  		spin_lock(&vfsmount_lock);

  		umount_tree(mnt, 0, &umount_list);

  		spin_unlock(&vfsmount_lock);

  		release_mounts(&umount_list);

  	}

  out:

  	up_write(&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 inline int tree_contains_unbindable(struct vfsmount *mnt)
  {
  	struct vfsmount *p;
  	for (p = mnt; p; p = next_mnt(p, mnt)) {
  		if (IS_MNT_UNBINDABLE(p))
  			return 1;
  	}
  	return 0;
  }

  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(&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;

  	mutex_lock(&nd->dentry->d_inode->i_mutex);

  	if (IS_DEADDIR(nd->dentry->d_inode))
  		goto out1;

  	if (!IS_ROOT(nd->dentry) && d_unhashed(nd->dentry))

  		goto out1;

  
  	err = -EINVAL;
  	if (old_nd.dentry != old_nd.mnt->mnt_root)

  		goto out1;

  
  	if (old_nd.mnt == old_nd.mnt->mnt_parent)

  		goto out1;

  
  	if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
  	      S_ISDIR(old_nd.dentry->d_inode->i_mode))

  		goto out1;
  	/*
  	 * Don't move a mount residing in a shared parent.
  	 */
  	if (old_nd.mnt->mnt_parent && IS_MNT_SHARED(old_nd.mnt->mnt_parent))
  		goto out1;

  	/*
  	 * Don't move a mount tree containing unbindable mounts to a destination
  	 * mount which is shared.
  	 */
  	if (IS_MNT_SHARED(nd->mnt) && tree_contains_unbindable(old_nd.mnt))
  		goto out1;

  	err = -ELOOP;

  	for (p = nd->mnt; p->mnt_parent != p; p = p->mnt_parent)

  		if (p == old_nd.mnt)

  			goto out1;

  	if ((err = attach_recursive_mnt(old_nd.mnt, nd, &parent_nd)))
  		goto out1;

  	spin_lock(&vfsmount_lock);

  	/* if the mount is moved, it should no longer be expire
  	 * automatically */

  	list_del_init(&old_nd.mnt->mnt_expire);

  	spin_unlock(&vfsmount_lock);
  out1:

  	mutex_unlock(&nd->dentry->d_inode->i_mutex);

  out:

  	up_write(&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(&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;

  	if ((err = graft_tree(newmnt, nd)))
  		goto unlock;

  	if (fslist) {

  		/* add to the specified expiration list */
  		spin_lock(&vfsmount_lock);

  		list_add_tail(&newmnt->mnt_expire, fslist);

  		spin_unlock(&vfsmount_lock);
  	}

  	up_write(&namespace_sem);

  	return 0;

  
  unlock:

  	up_write(&namespace_sem);

  	mntput(newmnt);
  	return err;
  }
  
  EXPORT_SYMBOL_GPL(do_add_mount);

  static void expire_mount(struct vfsmount *mnt, struct list_head *mounts,
  				struct list_head *umounts)

  {
  	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 (!propagate_mount_busy(mnt, 2)) {

  		/* delete from the namespace */

  		touch_mnt_namespace(mnt->mnt_ns);

  		list_del_init(&mnt->mnt_list);

  		mnt->mnt_ns = NULL;

  		umount_tree(mnt, 1, umounts);

  		spin_unlock(&vfsmount_lock);

  	} 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);
  	}
  }

  /*

   * 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
   */
  static void expire_mount_list(struct list_head *graveyard, struct list_head *mounts)
  {

  	struct mnt_namespace *ns;

  	struct vfsmount *mnt;
  
  	while (!list_empty(graveyard)) {
  		LIST_HEAD(umounts);

  		mnt = list_first_entry(graveyard, 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 */

  		ns = mnt->mnt_ns;
  		if (!ns || !ns->root)

  			continue;

  		get_mnt_ns(ns);

  
  		spin_unlock(&vfsmount_lock);
  		down_write(&namespace_sem);
  		expire_mount(mnt, mounts, &umounts);
  		up_write(&namespace_sem);
  		release_mounts(&umounts);
  		mntput(mnt);

  		put_mnt_ns(ns);

  		spin_lock(&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 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);

  	}

  	expire_mount_list(&graveyard, mounts);

  	spin_unlock(&vfsmount_lock);
  }
  
  EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
  
  /*
   * Ripoff of 'select_parent()'
   *
   * search the list of submounts for a given mountpoint, and move any
   * shrinkable submounts to the 'graveyard' list.
   */
  static int select_submounts(struct vfsmount *parent, struct list_head *graveyard)
  {
  	struct vfsmount *this_parent = parent;
  	struct list_head *next;
  	int found = 0;
  
  repeat:
  	next = this_parent->mnt_mounts.next;
  resume:
  	while (next != &this_parent->mnt_mounts) {
  		struct list_head *tmp = next;
  		struct vfsmount *mnt = list_entry(tmp, struct vfsmount, mnt_child);
  
  		next = tmp->next;
  		if (!(mnt->mnt_flags & MNT_SHRINKABLE))

  			continue;

  		/*
  		 * Descend a level if the d_mounts list is non-empty.
  		 */
  		if (!list_empty(&mnt->mnt_mounts)) {
  			this_parent = mnt;
  			goto repeat;
  		}

  		if (!propagate_mount_busy(mnt, 1)) {
  			mntget(mnt);
  			list_move_tail(&mnt->mnt_expire, graveyard);
  			found++;
  		}

  	}

  	/*
  	 * All done at this level ... ascend and resume the search
  	 */
  	if (this_parent != parent) {
  		next = this_parent->mnt_child.next;
  		this_parent = this_parent->mnt_parent;
  		goto resume;
  	}
  	return found;
  }
  
  /*
   * process a list of expirable mountpoints with the intent of discarding any
   * submounts of a specific parent mountpoint
   */
  void shrink_submounts(struct vfsmount *mountpoint, struct list_head *mounts)
  {
  	LIST_HEAD(graveyard);
  	int found;
  
  	spin_lock(&vfsmount_lock);
  
  	/* extract submounts of 'mountpoint' from the expiration list */
  	while ((found = select_submounts(mountpoint, &graveyard)) != 0)
  		expire_mount_list(&graveyard, mounts);

  
  	spin_unlock(&vfsmount_lock);
  }

  EXPORT_SYMBOL_GPL(shrink_submounts);

  
  /*
   * 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;

  	if (flags & MS_NOATIME)
  		mnt_flags |= MNT_NOATIME;
  	if (flags & MS_NODIRATIME)
  		mnt_flags |= MNT_NODIRATIME;

  	if (flags & MS_RELATIME)
  		mnt_flags |= MNT_RELATIME;

  
  	flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |

  		   MS_NOATIME | MS_NODIRATIME | MS_RELATIME);

  
  	/* ... 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_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))

  		retval = do_change_type(&nd, flags);

  	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;
  }

  /*
   * Allocate a new namespace structure and populate it with contents
   * copied from the namespace of the passed in task structure.
   */

  static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,

  		struct fs_struct *fs)

  {

  	struct mnt_namespace *new_ns;

  	struct vfsmount *rootmnt = NULL, *pwdmnt = NULL, *altrootmnt = NULL;

  	struct vfsmount *p, *q;

  	new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);

  	if (!new_ns)

  		return ERR_PTR(-ENOMEM);

  
  	atomic_set(&new_ns->count, 1);

  	INIT_LIST_HEAD(&new_ns->list);

  	init_waitqueue_head(&new_ns->poll);
  	new_ns->event = 0;

  	down_write(&namespace_sem);

  	/* First pass: copy the tree topology */

  	new_ns->root = copy_tree(mnt_ns->root, mnt_ns->root->mnt_root,

  					CL_COPY_ALL | CL_EXPIRE);

  	if (!new_ns->root) {

  		up_write(&namespace_sem);

  		kfree(new_ns);

  		return ERR_PTR(-ENOMEM);;

  	}
  	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 = mnt_ns->root;

  	q = new_ns->root;
  	while (p) {

  		q->mnt_ns = 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, mnt_ns->root);

  		q = next_mnt(q, new_ns->root);
  	}

  	up_write(&namespace_sem);

  	if (rootmnt)
  		mntput(rootmnt);
  	if (pwdmnt)
  		mntput(pwdmnt);
  	if (altrootmnt)
  		mntput(altrootmnt);

  	return new_ns;
  }

  struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,

  		struct fs_struct *new_fs)

  {

  	struct mnt_namespace *new_ns;

  	BUG_ON(!ns);

  	get_mnt_ns(ns);

  
  	if (!(flags & CLONE_NEWNS))

  		return ns;

  	new_ns = dup_mnt_ns(ns, new_fs);

  	put_mnt_ns(ns);

  	return new_ns;

  }
  
  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.
   *

   * Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
   * See Documentation/filesystems/ramfs-rootfs-initramfs.txt for alternatives
   * in this situation.
   *

   * 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(&namespace_sem);

  	mutex_lock(&old_nd.dentry->d_inode->i_mutex);

  	error = -EINVAL;

  	if (IS_MNT_SHARED(old_nd.mnt) ||
  		IS_MNT_SHARED(new_nd.mnt->mnt_parent) ||
  		IS_MNT_SHARED(user_nd.mnt->mnt_parent))
  		goto out2;

  	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 / */

  	touch_mnt_namespace(current->nsproxy->mnt_ns);

  	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:

  	mutex_unlock(&old_nd.dentry->d_inode->i_mutex);

  	up_write(&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 mnt_namespace *ns;

  
  	mnt = do_kern_mount("rootfs", 0, "rootfs", NULL);
  	if (IS_ERR(mnt))
  		panic("Can't create rootfs");

  	ns = kmalloc(sizeof(*ns), GFP_KERNEL);
  	if (!ns)

  		panic("Can't allocate initial namespace");

  	atomic_set(&ns->count, 1);
  	INIT_LIST_HEAD(&ns->list);
  	init_waitqueue_head(&ns->poll);
  	ns->event = 0;
  	list_add(&mnt->mnt_list, &ns->list);
  	ns->root = mnt;
  	mnt->mnt_ns = ns;
  
  	init_task.nsproxy->mnt_ns = ns;
  	get_mnt_ns(ns);
  
  	set_fs_pwd(current->fs, ns->root, ns->root->mnt_root);
  	set_fs_root(current->fs, ns->root, ns->root->mnt_root);

  }
  
  void __init mnt_init(unsigned long mempages)
  {
  	struct list_head *d;
  	unsigned int nr_hash;
  	int i;

  	int err;

  	init_rwsem(&namespace_sem);

  	mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct vfsmount),

  			0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);

  	mount_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);

  
  	if (!mount_hashtable)
  		panic("Failed to allocate mount hash table
  ");
  
  	/*
  	 * 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
  ", nr_hash);
  
  	/* And initialize the newly allocated array */
  	d = mount_hashtable;
  	i = nr_hash;
  	do {
  		INIT_LIST_HEAD(d);
  		d++;
  		i--;
  	} while (i);

  	err = sysfs_init();
  	if (err)
  		printk(KERN_WARNING "%s: sysfs_init error: %d
  ",
  			__FUNCTION__, err);
  	err = subsystem_register(&fs_subsys);
  	if (err)
  		printk(KERN_WARNING "%s: subsystem_register error: %d
  ",
  			__FUNCTION__, err);

  	init_rootfs();
  	init_mount_tree();
  }

  void __put_mnt_ns(struct mnt_namespace *ns)

  {

  	struct vfsmount *root = ns->root;

  	LIST_HEAD(umount_list);

  	ns->root = NULL;

  	spin_unlock(&vfsmount_lock);

  	down_write(&namespace_sem);

  	spin_lock(&vfsmount_lock);

  	umount_tree(root, 0, &umount_list);

  	spin_unlock(&vfsmount_lock);

  	up_write(&namespace_sem);

  	release_mounts(&umount_list);

  	kfree(ns);

  }