/* AFS file locking support
   *
   * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
   * Written by David Howells (dhowells@redhat.com)
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version
   * 2 of the License, or (at your option) any later version.
   */
  
  #include "internal.h"
  
  #define AFS_LOCK_GRANTED	0
  #define AFS_LOCK_PENDING	1
  
  static void afs_fl_copy_lock(struct file_lock *new, struct file_lock *fl);
  static void afs_fl_release_private(struct file_lock *fl);
  
  static struct workqueue_struct *afs_lock_manager;
  static DEFINE_MUTEX(afs_lock_manager_mutex);
  
  static const struct file_lock_operations afs_lock_ops = {
  	.fl_copy_lock		= afs_fl_copy_lock,
  	.fl_release_private	= afs_fl_release_private,
  };
  
  /*
   * initialise the lock manager thread if it isn't already running
   */
  static int afs_init_lock_manager(void)
  {
  	int ret;
  
  	ret = 0;
  	if (!afs_lock_manager) {
  		mutex_lock(&afs_lock_manager_mutex);
  		if (!afs_lock_manager) {
  			afs_lock_manager =
  				create_singlethread_workqueue("kafs_lockd");
  			if (!afs_lock_manager)
  				ret = -ENOMEM;
  		}
  		mutex_unlock(&afs_lock_manager_mutex);
  	}
  	return ret;
  }
  
  /*
   * destroy the lock manager thread if it's running
   */
  void __exit afs_kill_lock_manager(void)
  {
  	if (afs_lock_manager)
  		destroy_workqueue(afs_lock_manager);
  }
  
  /*
   * if the callback is broken on this vnode, then the lock may now be available
   */
  void afs_lock_may_be_available(struct afs_vnode *vnode)
  {
  	_enter("{%x:%u}", vnode->fid.vid, vnode->fid.vnode);
  
  	queue_delayed_work(afs_lock_manager, &vnode->lock_work, 0);
  }
  
  /*
   * the lock will time out in 5 minutes unless we extend it, so schedule
   * extension in a bit less than that time
   */
  static void afs_schedule_lock_extension(struct afs_vnode *vnode)
  {
  	queue_delayed_work(afs_lock_manager, &vnode->lock_work,
  			   AFS_LOCKWAIT * HZ / 2);
  }
  
  /*
   * grant one or more locks (readlocks are allowed to jump the queue if the
   * first lock in the queue is itself a readlock)
   * - the caller must hold the vnode lock
   */
  static void afs_grant_locks(struct afs_vnode *vnode, struct file_lock *fl)
  {
  	struct file_lock *p, *_p;
  
  	list_move_tail(&fl->fl_u.afs.link, &vnode->granted_locks);
  	if (fl->fl_type == F_RDLCK) {
  		list_for_each_entry_safe(p, _p, &vnode->pending_locks,
  					 fl_u.afs.link) {
  			if (p->fl_type == F_RDLCK) {
  				p->fl_u.afs.state = AFS_LOCK_GRANTED;
  				list_move_tail(&p->fl_u.afs.link,
  					       &vnode->granted_locks);
  				wake_up(&p->fl_wait);
  			}
  		}
  	}
  }
  
  /*
   * do work for a lock, including:
   * - probing for a lock we're waiting on but didn't get immediately
   * - extending a lock that's close to timing out
   */
  void afs_lock_work(struct work_struct *work)
  {
  	struct afs_vnode *vnode =
  		container_of(work, struct afs_vnode, lock_work.work);
  	struct file_lock *fl;
  	afs_lock_type_t type;
  	struct key *key;
  	int ret;
  
  	_enter("{%x:%u}", vnode->fid.vid, vnode->fid.vnode);
  
  	spin_lock(&vnode->lock);
  
  	if (test_bit(AFS_VNODE_UNLOCKING, &vnode->flags)) {
  		_debug("unlock");
  		spin_unlock(&vnode->lock);
  
  		/* attempt to release the server lock; if it fails, we just
  		 * wait 5 minutes and it'll time out anyway */
  		ret = afs_vnode_release_lock(vnode, vnode->unlock_key);
  		if (ret < 0)
  			printk(KERN_WARNING "AFS:"
  			       " Failed to release lock on {%x:%x} error %d
  ",
  			       vnode->fid.vid, vnode->fid.vnode, ret);
  
  		spin_lock(&vnode->lock);
  		key_put(vnode->unlock_key);
  		vnode->unlock_key = NULL;
  		clear_bit(AFS_VNODE_UNLOCKING, &vnode->flags);
  	}
  
  	/* if we've got a lock, then it must be time to extend that lock as AFS
  	 * locks time out after 5 minutes */
  	if (!list_empty(&vnode->granted_locks)) {
  		_debug("extend");
  
  		if (test_and_set_bit(AFS_VNODE_LOCKING, &vnode->flags))
  			BUG();
  		fl = list_entry(vnode->granted_locks.next,
  				struct file_lock, fl_u.afs.link);
  		key = key_get(fl->fl_file->private_data);
  		spin_unlock(&vnode->lock);
  
  		ret = afs_vnode_extend_lock(vnode, key);
  		clear_bit(AFS_VNODE_LOCKING, &vnode->flags);
  		key_put(key);
  		switch (ret) {
  		case 0:
  			afs_schedule_lock_extension(vnode);
  			break;
  		default:
  			/* ummm... we failed to extend the lock - retry
  			 * extension shortly */
  			printk(KERN_WARNING "AFS:"
  			       " Failed to extend lock on {%x:%x} error %d
  ",
  			       vnode->fid.vid, vnode->fid.vnode, ret);
  			queue_delayed_work(afs_lock_manager, &vnode->lock_work,
  					   HZ * 10);
  			break;
  		}
  		_leave(" [extend]");
  		return;
  	}
  
  	/* if we don't have a granted lock, then we must've been called back by
  	 * the server, and so if might be possible to get a lock we're
  	 * currently waiting for */
  	if (!list_empty(&vnode->pending_locks)) {
  		_debug("get");
  
  		if (test_and_set_bit(AFS_VNODE_LOCKING, &vnode->flags))
  			BUG();
  		fl = list_entry(vnode->pending_locks.next,
  				struct file_lock, fl_u.afs.link);
  		key = key_get(fl->fl_file->private_data);
  		type = (fl->fl_type == F_RDLCK) ?
  			AFS_LOCK_READ : AFS_LOCK_WRITE;
  		spin_unlock(&vnode->lock);
  
  		ret = afs_vnode_set_lock(vnode, key, type);
  		clear_bit(AFS_VNODE_LOCKING, &vnode->flags);
  		switch (ret) {
  		case -EWOULDBLOCK:
  			_debug("blocked");
  			break;
  		case 0:
  			_debug("acquired");
  			if (type == AFS_LOCK_READ)
  				set_bit(AFS_VNODE_READLOCKED, &vnode->flags);
  			else
  				set_bit(AFS_VNODE_WRITELOCKED, &vnode->flags);
  			ret = AFS_LOCK_GRANTED;
  		default:
  			spin_lock(&vnode->lock);
  			/* the pending lock may have been withdrawn due to a
  			 * signal */
  			if (list_entry(vnode->pending_locks.next,
  				       struct file_lock, fl_u.afs.link) == fl) {
  				fl->fl_u.afs.state = ret;
  				if (ret == AFS_LOCK_GRANTED)
  					afs_grant_locks(vnode, fl);
  				else
  					list_del_init(&fl->fl_u.afs.link);
  				wake_up(&fl->fl_wait);
  				spin_unlock(&vnode->lock);
  			} else {
  				_debug("withdrawn");
  				clear_bit(AFS_VNODE_READLOCKED, &vnode->flags);
  				clear_bit(AFS_VNODE_WRITELOCKED, &vnode->flags);
  				spin_unlock(&vnode->lock);
  				afs_vnode_release_lock(vnode, key);
  				if (!list_empty(&vnode->pending_locks))
  					afs_lock_may_be_available(vnode);
  			}
  			break;
  		}
  		key_put(key);
  		_leave(" [pend]");
  		return;
  	}
  
  	/* looks like the lock request was withdrawn on a signal */
  	spin_unlock(&vnode->lock);
  	_leave(" [no locks]");
  }
  
  /*
   * pass responsibility for the unlocking of a vnode on the server to the
   * manager thread, lest a pending signal in the calling thread interrupt
   * AF_RXRPC
   * - the caller must hold the vnode lock
   */
  static void afs_defer_unlock(struct afs_vnode *vnode, struct key *key)
  {
  	cancel_delayed_work(&vnode->lock_work);
  	if (!test_and_clear_bit(AFS_VNODE_READLOCKED, &vnode->flags) &&
  	    !test_and_clear_bit(AFS_VNODE_WRITELOCKED, &vnode->flags))
  		BUG();
  	if (test_and_set_bit(AFS_VNODE_UNLOCKING, &vnode->flags))
  		BUG();
  	vnode->unlock_key = key_get(key);
  	afs_lock_may_be_available(vnode);
  }
  
  /*
   * request a lock on a file on the server
   */
  static int afs_do_setlk(struct file *file, struct file_lock *fl)
  {
  	struct inode *inode = file_inode(file);
  	struct afs_vnode *vnode = AFS_FS_I(inode);
  	afs_lock_type_t type;
  	struct key *key = file->private_data;
  	int ret;
  
  	_enter("{%x:%u},%u", vnode->fid.vid, vnode->fid.vnode, fl->fl_type);
  
  	/* only whole-file locks are supported */
  	if (fl->fl_start != 0 || fl->fl_end != OFFSET_MAX)
  		return -EINVAL;
  
  	ret = afs_init_lock_manager();
  	if (ret < 0)
  		return ret;
  
  	fl->fl_ops = &afs_lock_ops;
  	INIT_LIST_HEAD(&fl->fl_u.afs.link);
  	fl->fl_u.afs.state = AFS_LOCK_PENDING;
  
  	type = (fl->fl_type == F_RDLCK) ? AFS_LOCK_READ : AFS_LOCK_WRITE;
  
  	spin_lock(&inode->i_lock);
  
  	/* make sure we've got a callback on this file and that our view of the
  	 * data version is up to date */
  	ret = afs_vnode_fetch_status(vnode, NULL, key);
  	if (ret < 0)
  		goto error;
  
  	if (vnode->status.lock_count != 0 && !(fl->fl_flags & FL_SLEEP)) {
  		ret = -EAGAIN;
  		goto error;
  	}
  
  	spin_lock(&vnode->lock);
  
  	/* if we've already got a readlock on the server then we can instantly
  	 * grant another readlock, irrespective of whether there are any
  	 * pending writelocks */
  	if (type == AFS_LOCK_READ &&
  	    vnode->flags & (1 << AFS_VNODE_READLOCKED)) {
  		_debug("instant readlock");
  		ASSERTCMP(vnode->flags &
  			  ((1 << AFS_VNODE_LOCKING) |
  			   (1 << AFS_VNODE_WRITELOCKED)), ==, 0);
  		ASSERT(!list_empty(&vnode->granted_locks));
  		goto sharing_existing_lock;
  	}
  
  	/* if there's no-one else with a lock on this vnode, then we need to
  	 * ask the server for a lock */
  	if (list_empty(&vnode->pending_locks) &&
  	    list_empty(&vnode->granted_locks)) {
  		_debug("not locked");
  		ASSERTCMP(vnode->flags &
  			  ((1 << AFS_VNODE_LOCKING) |
  			   (1 << AFS_VNODE_READLOCKED) |
  			   (1 << AFS_VNODE_WRITELOCKED)), ==, 0);
  		list_add_tail(&fl->fl_u.afs.link, &vnode->pending_locks);
  		set_bit(AFS_VNODE_LOCKING, &vnode->flags);
  		spin_unlock(&vnode->lock);
  
  		ret = afs_vnode_set_lock(vnode, key, type);
  		clear_bit(AFS_VNODE_LOCKING, &vnode->flags);
  		switch (ret) {
  		case 0:
  			_debug("acquired");
  			goto acquired_server_lock;
  		case -EWOULDBLOCK:
  			_debug("would block");
  			spin_lock(&vnode->lock);
  			ASSERT(list_empty(&vnode->granted_locks));
  			ASSERTCMP(vnode->pending_locks.next, ==,
  				  &fl->fl_u.afs.link);
  			goto wait;
  		default:
  			spin_lock(&vnode->lock);
  			list_del_init(&fl->fl_u.afs.link);
  			spin_unlock(&vnode->lock);
  			goto error;
  		}
  	}
  
  	/* otherwise, we need to wait for a local lock to become available */
  	_debug("wait local");
  	list_add_tail(&fl->fl_u.afs.link, &vnode->pending_locks);
  wait:
  	if (!(fl->fl_flags & FL_SLEEP)) {
  		_debug("noblock");
  		ret = -EAGAIN;
  		goto abort_attempt;
  	}
  	spin_unlock(&vnode->lock);
  
  	/* now we need to sleep and wait for the lock manager thread to get the
  	 * lock from the server */
  	_debug("sleep");
  	ret = wait_event_interruptible(fl->fl_wait,
  				       fl->fl_u.afs.state <= AFS_LOCK_GRANTED);
  	if (fl->fl_u.afs.state <= AFS_LOCK_GRANTED) {
  		ret = fl->fl_u.afs.state;
  		if (ret < 0)
  			goto error;
  		spin_lock(&vnode->lock);
  		goto given_lock;
  	}
  
  	/* we were interrupted, but someone may still be in the throes of
  	 * giving us the lock */
  	_debug("intr");
  	ASSERTCMP(ret, ==, -ERESTARTSYS);
  
  	spin_lock(&vnode->lock);
  	if (fl->fl_u.afs.state <= AFS_LOCK_GRANTED) {
  		ret = fl->fl_u.afs.state;
  		if (ret < 0) {
  			spin_unlock(&vnode->lock);
  			goto error;
  		}
  		goto given_lock;
  	}
  
  abort_attempt:
  	/* we aren't going to get the lock, either because we're unwilling to
  	 * wait, or because some signal happened */
  	_debug("abort");
  	if (list_empty(&vnode->granted_locks) &&
  	    vnode->pending_locks.next == &fl->fl_u.afs.link) {
  		if (vnode->pending_locks.prev != &fl->fl_u.afs.link) {
  			/* kick the next pending lock into having a go */
  			list_del_init(&fl->fl_u.afs.link);
  			afs_lock_may_be_available(vnode);
  		}
  	} else {
  		list_del_init(&fl->fl_u.afs.link);
  	}
  	spin_unlock(&vnode->lock);
  	goto error;
  
  acquired_server_lock:
  	/* we've acquired a server lock, but it needs to be renewed after 5
  	 * mins */
  	spin_lock(&vnode->lock);
  	afs_schedule_lock_extension(vnode);
  	if (type == AFS_LOCK_READ)
  		set_bit(AFS_VNODE_READLOCKED, &vnode->flags);
  	else
  		set_bit(AFS_VNODE_WRITELOCKED, &vnode->flags);
  sharing_existing_lock:
  	/* the lock has been granted as far as we're concerned... */
  	fl->fl_u.afs.state = AFS_LOCK_GRANTED;
  	list_move_tail(&fl->fl_u.afs.link, &vnode->granted_locks);
  given_lock:
  	/* ... but we do still need to get the VFS's blessing */
  	ASSERT(!(vnode->flags & (1 << AFS_VNODE_LOCKING)));
  	ASSERT((vnode->flags & ((1 << AFS_VNODE_READLOCKED) |
  				(1 << AFS_VNODE_WRITELOCKED))) != 0);
  	ret = posix_lock_file(file, fl, NULL);
  	if (ret < 0)
  		goto vfs_rejected_lock;
  	spin_unlock(&vnode->lock);
  
  	/* again, make sure we've got a callback on this file and, again, make
  	 * sure that our view of the data version is up to date (we ignore
  	 * errors incurred here and deal with the consequences elsewhere) */
  	afs_vnode_fetch_status(vnode, NULL, key);
  
  error:
  	spin_unlock(&inode->i_lock);
  	_leave(" = %d", ret);
  	return ret;
  
  vfs_rejected_lock:
  	/* the VFS rejected the lock we just obtained, so we have to discard
  	 * what we just got */
  	_debug("vfs refused %d", ret);
  	list_del_init(&fl->fl_u.afs.link);
  	if (list_empty(&vnode->granted_locks))
  		afs_defer_unlock(vnode, key);
  	goto abort_attempt;
  }
  
  /*
   * unlock on a file on the server
   */
  static int afs_do_unlk(struct file *file, struct file_lock *fl)
  {
  	struct afs_vnode *vnode = AFS_FS_I(file->f_mapping->host);
  	struct key *key = file->private_data;
  	int ret;
  
  	_enter("{%x:%u},%u", vnode->fid.vid, vnode->fid.vnode, fl->fl_type);
  
  	/* only whole-file unlocks are supported */
  	if (fl->fl_start != 0 || fl->fl_end != OFFSET_MAX)
  		return -EINVAL;
  
  	fl->fl_ops = &afs_lock_ops;
  	INIT_LIST_HEAD(&fl->fl_u.afs.link);
  	fl->fl_u.afs.state = AFS_LOCK_PENDING;
  
  	spin_lock(&vnode->lock);
  	ret = posix_lock_file(file, fl, NULL);
  	if (ret < 0) {
  		spin_unlock(&vnode->lock);
  		_leave(" = %d [vfs]", ret);
  		return ret;
  	}
  
  	/* discard the server lock only if all granted locks are gone */
  	if (list_empty(&vnode->granted_locks))
  		afs_defer_unlock(vnode, key);
  	spin_unlock(&vnode->lock);
  	_leave(" = 0");
  	return 0;
  }
  
  /*
   * return information about a lock we currently hold, if indeed we hold one
   */
  static int afs_do_getlk(struct file *file, struct file_lock *fl)
  {
  	struct afs_vnode *vnode = AFS_FS_I(file->f_mapping->host);
  	struct key *key = file->private_data;
  	int ret, lock_count;
  
  	_enter("");
  
  	fl->fl_type = F_UNLCK;
  
  	mutex_lock(&vnode->vfs_inode.i_mutex);
  
  	/* check local lock records first */
  	ret = 0;
  	posix_test_lock(file, fl);
  	if (fl->fl_type == F_UNLCK) {
  		/* no local locks; consult the server */
  		ret = afs_vnode_fetch_status(vnode, NULL, key);
  		if (ret < 0)
  			goto error;
  		lock_count = vnode->status.lock_count;
  		if (lock_count) {
  			if (lock_count > 0)
  				fl->fl_type = F_RDLCK;
  			else
  				fl->fl_type = F_WRLCK;
  			fl->fl_start = 0;
  			fl->fl_end = OFFSET_MAX;
  		}
  	}
  
  error:
  	mutex_unlock(&vnode->vfs_inode.i_mutex);
  	_leave(" = %d [%hd]", ret, fl->fl_type);
  	return ret;
  }
  
  /*
   * manage POSIX locks on a file
   */
  int afs_lock(struct file *file, int cmd, struct file_lock *fl)
  {
  	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
  
  	_enter("{%x:%u},%d,{t=%x,fl=%x,r=%Ld:%Ld}",
  	       vnode->fid.vid, vnode->fid.vnode, cmd,
  	       fl->fl_type, fl->fl_flags,
  	       (long long) fl->fl_start, (long long) fl->fl_end);
  
  	/* AFS doesn't support mandatory locks */
  	if (__mandatory_lock(&vnode->vfs_inode) && fl->fl_type != F_UNLCK)
  		return -ENOLCK;
  
  	if (IS_GETLK(cmd))
  		return afs_do_getlk(file, fl);
  	if (fl->fl_type == F_UNLCK)
  		return afs_do_unlk(file, fl);
  	return afs_do_setlk(file, fl);
  }
  
  /*
   * manage FLOCK locks on a file
   */
  int afs_flock(struct file *file, int cmd, struct file_lock *fl)
  {
  	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
  
  	_enter("{%x:%u},%d,{t=%x,fl=%x}",
  	       vnode->fid.vid, vnode->fid.vnode, cmd,
  	       fl->fl_type, fl->fl_flags);
  
  	/*
  	 * No BSD flocks over NFS allowed.
  	 * Note: we could try to fake a POSIX lock request here by
  	 * using ((u32) filp | 0x80000000) or some such as the pid.
  	 * Not sure whether that would be unique, though, or whether
  	 * that would break in other places.
  	 */
  	if (!(fl->fl_flags & FL_FLOCK))
  		return -ENOLCK;
  
  	/* we're simulating flock() locks using posix locks on the server */
  	fl->fl_owner = (fl_owner_t) file;
  	fl->fl_start = 0;
  	fl->fl_end = OFFSET_MAX;
  
  	if (fl->fl_type == F_UNLCK)
  		return afs_do_unlk(file, fl);
  	return afs_do_setlk(file, fl);
  }
  
  /*
   * the POSIX lock management core VFS code copies the lock record and adds the
   * copy into its own list, so we need to add that copy to the vnode's lock
   * queue in the same place as the original (which will be deleted shortly
   * after)
   */
  static void afs_fl_copy_lock(struct file_lock *new, struct file_lock *fl)
  {
  	_enter("");
  
  	list_add(&new->fl_u.afs.link, &fl->fl_u.afs.link);
  }
  
  /*
   * need to remove this lock from the vnode queue when it's removed from the
   * VFS's list
   */
  static void afs_fl_release_private(struct file_lock *fl)
  {
  	_enter("");
  
  	list_del_init(&fl->fl_u.afs.link);
  }