/* -*- c -*- --------------------------------------------------------------- *
   *
   * linux/fs/autofs/expire.c
   *
   *  Copyright 1997-1998 Transmeta Corporation -- All Rights Reserved
   *  Copyright 1999-2000 Jeremy Fitzhardinge <jeremy@goop.org>
   *  Copyright 2001-2006 Ian Kent <raven@themaw.net>
   *
   * This file is part of the Linux kernel and is made available under
   * the terms of the GNU General Public License, version 2, or at your
   * option, any later version, incorporated herein by reference.
   *
   * ------------------------------------------------------------------------- */
  
  #include "autofs_i.h"
  
  static unsigned long now;
  
  /* Check if a dentry can be expired */
  static inline int autofs4_can_expire(struct dentry *dentry,
  					unsigned long timeout, int do_now)
  {
  	struct autofs_info *ino = autofs4_dentry_ino(dentry);
  
  	/* dentry in the process of being deleted */
  	if (ino == NULL)
  		return 0;
  
  	if (!do_now) {
  		/* Too young to die */
  		if (!timeout || time_after(ino->last_used + timeout, now))
  			return 0;
  
  		/* update last_used here :-
  		   - obviously makes sense if it is in use now
  		   - less obviously, prevents rapid-fire expire
  		     attempts if expire fails the first time */
  		ino->last_used = now;
  	}
  	return 1;
  }
  
  /* Check a mount point for busyness */
  static int autofs4_mount_busy(struct vfsmount *mnt, struct dentry *dentry)
  {
  	struct dentry *top = dentry;
  	struct path path = {.mnt = mnt, .dentry = dentry};
  	int status = 1;
  
  	DPRINTK("dentry %p %.*s",
  		dentry, (int)dentry->d_name.len, dentry->d_name.name);
  
  	path_get(&path);
  
  	if (!follow_down_one(&path))
  		goto done;
  
  	if (is_autofs4_dentry(path.dentry)) {
  		struct autofs_sb_info *sbi = autofs4_sbi(path.dentry->d_sb);
  
  		/* This is an autofs submount, we can't expire it */
  		if (autofs_type_indirect(sbi->type))
  			goto done;
  	}
  
  	/* Update the expiry counter if fs is busy */
  	if (!may_umount_tree(path.mnt)) {
  		struct autofs_info *ino = autofs4_dentry_ino(top);
  		ino->last_used = jiffies;
  		goto done;
  	}
  
  	status = 0;
  done:
  	DPRINTK("returning = %d", status);
  	path_put(&path);
  	return status;
  }
  
  /*
   * Calculate and dget next entry in the subdirs list under root.
   */
  static struct dentry *get_next_positive_subdir(struct dentry *prev,
  						struct dentry *root)
  {
  	struct autofs_sb_info *sbi = autofs4_sbi(root->d_sb);
  	struct list_head *next;
  	struct dentry *q;
  
  	spin_lock(&sbi->lookup_lock);
  	spin_lock(&root->d_lock);
  
  	if (prev)
  		next = prev->d_u.d_child.next;
  	else {
  		prev = dget_dlock(root);
  		next = prev->d_subdirs.next;
  	}
  
  cont:
  	if (next == &root->d_subdirs) {
  		spin_unlock(&root->d_lock);
  		spin_unlock(&sbi->lookup_lock);
  		dput(prev);
  		return NULL;
  	}
  
  	q = list_entry(next, struct dentry, d_u.d_child);
  
  	spin_lock_nested(&q->d_lock, DENTRY_D_LOCK_NESTED);
  	/* Already gone or negative dentry (under construction) - try next */
  	if (!d_count(q) || !simple_positive(q)) {
  		spin_unlock(&q->d_lock);
  		next = q->d_u.d_child.next;
  		goto cont;
  	}
  	dget_dlock(q);
  	spin_unlock(&q->d_lock);
  	spin_unlock(&root->d_lock);
  	spin_unlock(&sbi->lookup_lock);
  
  	dput(prev);
  
  	return q;
  }
  
  /*
   * Calculate and dget next entry in top down tree traversal.
   */
  static struct dentry *get_next_positive_dentry(struct dentry *prev,
  						struct dentry *root)
  {
  	struct autofs_sb_info *sbi = autofs4_sbi(root->d_sb);
  	struct list_head *next;
  	struct dentry *p, *ret;
  
  	if (prev == NULL)
  		return dget(root);
  
  	spin_lock(&sbi->lookup_lock);
  relock:
  	p = prev;
  	spin_lock(&p->d_lock);
  again:
  	next = p->d_subdirs.next;
  	if (next == &p->d_subdirs) {
  		while (1) {
  			struct dentry *parent;
  
  			if (p == root) {
  				spin_unlock(&p->d_lock);
  				spin_unlock(&sbi->lookup_lock);
  				dput(prev);
  				return NULL;
  			}
  
  			parent = p->d_parent;
  			if (!spin_trylock(&parent->d_lock)) {
  				spin_unlock(&p->d_lock);
  				cpu_relax();
  				goto relock;
  			}
  			spin_unlock(&p->d_lock);
  			next = p->d_u.d_child.next;
  			p = parent;
  			if (next != &parent->d_subdirs)
  				break;
  		}
  	}
  	ret = list_entry(next, struct dentry, d_u.d_child);
  
  	spin_lock_nested(&ret->d_lock, DENTRY_D_LOCK_NESTED);
  	/* Negative dentry - try next */
  	if (!simple_positive(ret)) {
  		spin_unlock(&p->d_lock);
  		lock_set_subclass(&ret->d_lock.dep_map, 0, _RET_IP_);
  		p = ret;
  		goto again;
  	}
  	dget_dlock(ret);
  	spin_unlock(&ret->d_lock);
  	spin_unlock(&p->d_lock);
  	spin_unlock(&sbi->lookup_lock);
  
  	dput(prev);
  
  	return ret;
  }
  
  /*
   * Check a direct mount point for busyness.
   * Direct mounts have similar expiry semantics to tree mounts.
   * The tree is not busy iff no mountpoints are busy and there are no
   * autofs submounts.
   */
  static int autofs4_direct_busy(struct vfsmount *mnt,
  				struct dentry *top,
  				unsigned long timeout,
  				int do_now)
  {
  	DPRINTK("top %p %.*s",
  		top, (int) top->d_name.len, top->d_name.name);
  
  	/* If it's busy update the expiry counters */
  	if (!may_umount_tree(mnt)) {
  		struct autofs_info *ino = autofs4_dentry_ino(top);
  		if (ino)
  			ino->last_used = jiffies;
  		return 1;
  	}
  
  	/* Timeout of a direct mount is determined by its top dentry */
  	if (!autofs4_can_expire(top, timeout, do_now))
  		return 1;
  
  	return 0;
  }
  
  /* Check a directory tree of mount points for busyness
   * The tree is not busy iff no mountpoints are busy
   */
  static int autofs4_tree_busy(struct vfsmount *mnt,
  	       		     struct dentry *top,
  			     unsigned long timeout,
  			     int do_now)
  {
  	struct autofs_info *top_ino = autofs4_dentry_ino(top);
  	struct dentry *p;
  
  	DPRINTK("top %p %.*s",
  		top, (int)top->d_name.len, top->d_name.name);
  
  	/* Negative dentry - give up */
  	if (!simple_positive(top))
  		return 1;
  
  	p = NULL;
  	while ((p = get_next_positive_dentry(p, top))) {
  		DPRINTK("dentry %p %.*s",
  			p, (int) p->d_name.len, p->d_name.name);
  
  		/*
  		 * Is someone visiting anywhere in the subtree ?
  		 * If there's no mount we need to check the usage
  		 * count for the autofs dentry.
  		 * If the fs is busy update the expiry counter.
  		 */
  		if (d_mountpoint(p)) {
  			if (autofs4_mount_busy(mnt, p)) {
  				top_ino->last_used = jiffies;
  				dput(p);
  				return 1;
  			}
  		} else {
  			struct autofs_info *ino = autofs4_dentry_ino(p);
  			unsigned int ino_count = atomic_read(&ino->count);
  
  			/*
  			 * Clean stale dentries below that have not been
  			 * invalidated after a mount fail during lookup
  			 */
  			d_invalidate(p);
  
  			/* allow for dget above and top is already dgot */
  			if (p == top)
  				ino_count += 2;
  			else
  				ino_count++;
  
  			if (d_count(p) > ino_count) {
  				top_ino->last_used = jiffies;
  				dput(p);
  				return 1;
  			}
  		}
  	}
  
  	/* Timeout of a tree mount is ultimately determined by its top dentry */
  	if (!autofs4_can_expire(top, timeout, do_now))
  		return 1;
  
  	return 0;
  }
  
  static struct dentry *autofs4_check_leaves(struct vfsmount *mnt,
  					   struct dentry *parent,
  					   unsigned long timeout,
  					   int do_now)
  {
  	struct dentry *p;
  
  	DPRINTK("parent %p %.*s",
  		parent, (int)parent->d_name.len, parent->d_name.name);
  
  	p = NULL;
  	while ((p = get_next_positive_dentry(p, parent))) {
  		DPRINTK("dentry %p %.*s",
  			p, (int) p->d_name.len, p->d_name.name);
  
  		if (d_mountpoint(p)) {
  			/* Can we umount this guy */
  			if (autofs4_mount_busy(mnt, p))
  				continue;
  
  			/* Can we expire this guy */
  			if (autofs4_can_expire(p, timeout, do_now))
  				return p;
  		}
  	}
  	return NULL;
  }
  
  /* Check if we can expire a direct mount (possibly a tree) */
  struct dentry *autofs4_expire_direct(struct super_block *sb,
  				     struct vfsmount *mnt,
  				     struct autofs_sb_info *sbi,
  				     int how)
  {
  	unsigned long timeout;
  	struct dentry *root = dget(sb->s_root);
  	int do_now = how & AUTOFS_EXP_IMMEDIATE;
  	struct autofs_info *ino;
  
  	if (!root)
  		return NULL;
  
  	now = jiffies;
  	timeout = sbi->exp_timeout;
  
  	spin_lock(&sbi->fs_lock);
  	ino = autofs4_dentry_ino(root);
  	/* No point expiring a pending mount */
  	if (ino->flags & AUTOFS_INF_PENDING)
  		goto out;
  	if (!autofs4_direct_busy(mnt, root, timeout, do_now)) {
  		struct autofs_info *ino = autofs4_dentry_ino(root);
  		ino->flags |= AUTOFS_INF_EXPIRING;
  		init_completion(&ino->expire_complete);
  		spin_unlock(&sbi->fs_lock);
  		return root;
  	}
  out:
  	spin_unlock(&sbi->fs_lock);
  	dput(root);
  
  	return NULL;
  }
  
  /*
   * Find an eligible tree to time-out
   * A tree is eligible if :-
   *  - it is unused by any user process
   *  - it has been unused for exp_timeout time
   */
  struct dentry *autofs4_expire_indirect(struct super_block *sb,
  				       struct vfsmount *mnt,
  				       struct autofs_sb_info *sbi,
  				       int how)
  {
  	unsigned long timeout;
  	struct dentry *root = sb->s_root;
  	struct dentry *dentry;
  	struct dentry *expired = NULL;
  	int do_now = how & AUTOFS_EXP_IMMEDIATE;
  	int exp_leaves = how & AUTOFS_EXP_LEAVES;
  	struct autofs_info *ino;
  	unsigned int ino_count;
  
  	if (!root)
  		return NULL;
  
  	now = jiffies;
  	timeout = sbi->exp_timeout;
  
  	dentry = NULL;
  	while ((dentry = get_next_positive_subdir(dentry, root))) {
  		spin_lock(&sbi->fs_lock);
  		ino = autofs4_dentry_ino(dentry);
  		/* No point expiring a pending mount */
  		if (ino->flags & AUTOFS_INF_PENDING)
  			goto next;
  
  		/*
  		 * Case 1: (i) indirect mount or top level pseudo direct mount
  		 *	   (autofs-4.1).
  		 *	   (ii) indirect mount with offset mount, check the "/"
  		 *	   offset (autofs-5.0+).
  		 */
  		if (d_mountpoint(dentry)) {
  			DPRINTK("checking mountpoint %p %.*s",
  				dentry, (int)dentry->d_name.len, dentry->d_name.name);
  
  			/* Can we umount this guy */
  			if (autofs4_mount_busy(mnt, dentry))
  				goto next;
  
  			/* Can we expire this guy */
  			if (autofs4_can_expire(dentry, timeout, do_now)) {
  				expired = dentry;
  				goto found;
  			}
  			goto next;
  		}
  
  		if (dentry->d_inode && S_ISLNK(dentry->d_inode->i_mode)) {
  			DPRINTK("checking symlink %p %.*s",
  				dentry, (int)dentry->d_name.len, dentry->d_name.name);
  			/*
  			 * A symlink can't be "busy" in the usual sense so
  			 * just check last used for expire timeout.
  			 */
  			if (autofs4_can_expire(dentry, timeout, do_now)) {
  				expired = dentry;
  				goto found;
  			}
  			goto next;
  		}
  
  		if (simple_empty(dentry))
  			goto next;
  
  		/* Case 2: tree mount, expire iff entire tree is not busy */
  		if (!exp_leaves) {
  			/* Path walk currently on this dentry? */
  			ino_count = atomic_read(&ino->count) + 1;
  			if (d_count(dentry) > ino_count)
  				goto next;
  
  			if (!autofs4_tree_busy(mnt, dentry, timeout, do_now)) {
  				expired = dentry;
  				goto found;
  			}
  		/*
  		 * Case 3: pseudo direct mount, expire individual leaves
  		 *	   (autofs-4.1).
  		 */
  		} else {
  			/* Path walk currently on this dentry? */
  			ino_count = atomic_read(&ino->count) + 1;
  			if (d_count(dentry) > ino_count)
  				goto next;
  
  			expired = autofs4_check_leaves(mnt, dentry, timeout, do_now);
  			if (expired) {
  				dput(dentry);
  				goto found;
  			}
  		}
  next:
  		spin_unlock(&sbi->fs_lock);
  	}
  	return NULL;
  
  found:
  	DPRINTK("returning %p %.*s",
  		expired, (int)expired->d_name.len, expired->d_name.name);
  	ino = autofs4_dentry_ino(expired);
  	ino->flags |= AUTOFS_INF_EXPIRING;
  	init_completion(&ino->expire_complete);
  	spin_unlock(&sbi->fs_lock);
  	spin_lock(&sbi->lookup_lock);
  	spin_lock(&expired->d_parent->d_lock);
  	spin_lock_nested(&expired->d_lock, DENTRY_D_LOCK_NESTED);
  	list_move(&expired->d_parent->d_subdirs, &expired->d_u.d_child);
  	spin_unlock(&expired->d_lock);
  	spin_unlock(&expired->d_parent->d_lock);
  	spin_unlock(&sbi->lookup_lock);
  	return expired;
  }
  
  int autofs4_expire_wait(struct dentry *dentry)
  {
  	struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb);
  	struct autofs_info *ino = autofs4_dentry_ino(dentry);
  	int status;
  
  	/* Block on any pending expire */
  	spin_lock(&sbi->fs_lock);
  	if (ino->flags & AUTOFS_INF_EXPIRING) {
  		spin_unlock(&sbi->fs_lock);
  
  		DPRINTK("waiting for expire %p name=%.*s",
  			 dentry, dentry->d_name.len, dentry->d_name.name);
  
  		status = autofs4_wait(sbi, dentry, NFY_NONE);
  		wait_for_completion(&ino->expire_complete);
  
  		DPRINTK("expire done status=%d", status);
  
  		if (d_unhashed(dentry))
  			return -EAGAIN;
  
  		return status;
  	}
  	spin_unlock(&sbi->fs_lock);
  
  	return 0;
  }
  
  /* Perform an expiry operation */
  int autofs4_expire_run(struct super_block *sb,
  		      struct vfsmount *mnt,
  		      struct autofs_sb_info *sbi,
  		      struct autofs_packet_expire __user *pkt_p)
  {
  	struct autofs_packet_expire pkt;
  	struct autofs_info *ino;
  	struct dentry *dentry;
  	int ret = 0;
  
  	memset(&pkt,0,sizeof pkt);
  
  	pkt.hdr.proto_version = sbi->version;
  	pkt.hdr.type = autofs_ptype_expire;
  
  	if ((dentry = autofs4_expire_indirect(sb, mnt, sbi, 0)) == NULL)
  		return -EAGAIN;
  
  	pkt.len = dentry->d_name.len;
  	memcpy(pkt.name, dentry->d_name.name, pkt.len);
  	pkt.name[pkt.len] = '\0';
  	dput(dentry);
  
  	if ( copy_to_user(pkt_p, &pkt, sizeof(struct autofs_packet_expire)) )
  		ret = -EFAULT;
  
  	spin_lock(&sbi->fs_lock);
  	ino = autofs4_dentry_ino(dentry);
  	ino->flags &= ~AUTOFS_INF_EXPIRING;
  	complete_all(&ino->expire_complete);
  	spin_unlock(&sbi->fs_lock);
  
  	return ret;
  }
  
  int autofs4_do_expire_multi(struct super_block *sb, struct vfsmount *mnt,
  			    struct autofs_sb_info *sbi, int when)
  {
  	struct dentry *dentry;
  	int ret = -EAGAIN;
  
  	if (autofs_type_trigger(sbi->type))
  		dentry = autofs4_expire_direct(sb, mnt, sbi, when);
  	else
  		dentry = autofs4_expire_indirect(sb, mnt, sbi, when);
  
  	if (dentry) {
  		struct autofs_info *ino = autofs4_dentry_ino(dentry);
  
  		/* This is synchronous because it makes the daemon a
                     little easier */
  		ret = autofs4_wait(sbi, dentry, NFY_EXPIRE);
  
  		spin_lock(&sbi->fs_lock);
  		ino->flags &= ~AUTOFS_INF_EXPIRING;
  		complete_all(&ino->expire_complete);
  		spin_unlock(&sbi->fs_lock);
  		dput(dentry);
  	}
  
  	return ret;
  }
  
  /* Call repeatedly until it returns -EAGAIN, meaning there's nothing
     more to be done */
  int autofs4_expire_multi(struct super_block *sb, struct vfsmount *mnt,
  			struct autofs_sb_info *sbi, int __user *arg)
  {
  	int do_now = 0;
  
  	if (arg && get_user(do_now, arg))
  		return -EFAULT;
  
  	return autofs4_do_expire_multi(sb, mnt, sbi, do_now);
  }