/*
   * Copyright (c) 2002, 2007 Red Hat, Inc. All rights reserved.
   *
   * This software may be freely redistributed under the terms of the
   * GNU General Public License.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
   *
   * Authors: David Woodhouse <dwmw2@infradead.org>
   *          David Howells <dhowells@redhat.com>
   *
   */
  
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/circ_buf.h>
  #include <linux/sched.h>
  #include "internal.h"
  
  #if 0
  unsigned afs_vnode_update_timeout = 10;
  #endif  /*  0  */
  
  #define afs_breakring_space(server) \
  	CIRC_SPACE((server)->cb_break_head, (server)->cb_break_tail,	\
  		   ARRAY_SIZE((server)->cb_break))
  
  //static void afs_callback_updater(struct work_struct *);
  
  static struct workqueue_struct *afs_callback_update_worker;
  
  /*
   * allow the fileserver to request callback state (re-)initialisation
   */
  void afs_init_callback_state(struct afs_server *server)
  {
  	struct afs_vnode *vnode;
  
  	_enter("{%p}", server);
  
  	spin_lock(&server->cb_lock);
  
  	/* kill all the promises on record from this server */
  	while (!RB_EMPTY_ROOT(&server->cb_promises)) {
  		vnode = rb_entry(server->cb_promises.rb_node,
  				 struct afs_vnode, cb_promise);
  		_debug("UNPROMISE { vid=%x:%u uq=%u}",
  		       vnode->fid.vid, vnode->fid.vnode, vnode->fid.unique);
  		rb_erase(&vnode->cb_promise, &server->cb_promises);
  		vnode->cb_promised = false;
  	}
  
  	spin_unlock(&server->cb_lock);
  	_leave("");
  }
  
  /*
   * handle the data invalidation side of a callback being broken
   */
  void afs_broken_callback_work(struct work_struct *work)
  {
  	struct afs_vnode *vnode =
  		container_of(work, struct afs_vnode, cb_broken_work);
  
  	_enter("");
  
  	if (test_bit(AFS_VNODE_DELETED, &vnode->flags))
  		return;
  
  	/* we're only interested in dealing with a broken callback on *this*
  	 * vnode and only if no-one else has dealt with it yet */
  	if (!mutex_trylock(&vnode->validate_lock))
  		return; /* someone else is dealing with it */
  
  	if (test_bit(AFS_VNODE_CB_BROKEN, &vnode->flags)) {
  		if (S_ISDIR(vnode->vfs_inode.i_mode))
  			afs_clear_permits(vnode);
  
  		if (afs_vnode_fetch_status(vnode, NULL, NULL) < 0)
  			goto out;
  
  		if (test_bit(AFS_VNODE_DELETED, &vnode->flags))
  			goto out;
  
  		/* if the vnode's data version number changed then its contents
  		 * are different */
  		if (test_and_clear_bit(AFS_VNODE_ZAP_DATA, &vnode->flags))
  			afs_zap_data(vnode);
  	}
  
  out:
  	mutex_unlock(&vnode->validate_lock);
  
  	/* avoid the potential race whereby the mutex_trylock() in this
  	 * function happens again between the clear_bit() and the
  	 * mutex_unlock() */
  	if (test_bit(AFS_VNODE_CB_BROKEN, &vnode->flags)) {
  		_debug("requeue");
  		queue_work(afs_callback_update_worker, &vnode->cb_broken_work);
  	}
  	_leave("");
  }
  
  /*
   * actually break a callback
   */
  static void afs_break_callback(struct afs_server *server,
  			       struct afs_vnode *vnode)
  {
  	_enter("");
  
  	set_bit(AFS_VNODE_CB_BROKEN, &vnode->flags);
  
  	if (vnode->cb_promised) {
  		spin_lock(&vnode->lock);
  
  		_debug("break callback");
  
  		spin_lock(&server->cb_lock);
  		if (vnode->cb_promised) {
  			rb_erase(&vnode->cb_promise, &server->cb_promises);
  			vnode->cb_promised = false;
  		}
  		spin_unlock(&server->cb_lock);
  
  		queue_work(afs_callback_update_worker, &vnode->cb_broken_work);
  		if (list_empty(&vnode->granted_locks) &&
  		    !list_empty(&vnode->pending_locks))
  			afs_lock_may_be_available(vnode);
  		spin_unlock(&vnode->lock);
  	}
  }
  
  /*
   * allow the fileserver to explicitly break one callback
   * - happens when
   *   - the backing file is changed
   *   - a lock is released
   */
  static void afs_break_one_callback(struct afs_server *server,
  				   struct afs_fid *fid)
  {
  	struct afs_vnode *vnode;
  	struct rb_node *p;
  
  	_debug("find");
  	spin_lock(&server->fs_lock);
  	p = server->fs_vnodes.rb_node;
  	while (p) {
  		vnode = rb_entry(p, struct afs_vnode, server_rb);
  		if (fid->vid < vnode->fid.vid)
  			p = p->rb_left;
  		else if (fid->vid > vnode->fid.vid)
  			p = p->rb_right;
  		else if (fid->vnode < vnode->fid.vnode)
  			p = p->rb_left;
  		else if (fid->vnode > vnode->fid.vnode)
  			p = p->rb_right;
  		else if (fid->unique < vnode->fid.unique)
  			p = p->rb_left;
  		else if (fid->unique > vnode->fid.unique)
  			p = p->rb_right;
  		else
  			goto found;
  	}
  
  	/* not found so we just ignore it (it may have moved to another
  	 * server) */
  not_available:
  	_debug("not avail");
  	spin_unlock(&server->fs_lock);
  	_leave("");
  	return;
  
  found:
  	_debug("found");
  	ASSERTCMP(server, ==, vnode->server);
  
  	if (!igrab(AFS_VNODE_TO_I(vnode)))
  		goto not_available;
  	spin_unlock(&server->fs_lock);
  
  	afs_break_callback(server, vnode);
  	iput(&vnode->vfs_inode);
  	_leave("");
  }
  
  /*
   * allow the fileserver to break callback promises
   */
  void afs_break_callbacks(struct afs_server *server, size_t count,
  			 struct afs_callback callbacks[])
  {
  	_enter("%p,%zu,", server, count);
  
  	ASSERT(server != NULL);
  	ASSERTCMP(count, <=, AFSCBMAX);
  
  	for (; count > 0; callbacks++, count--) {
  		_debug("- Fid { vl=%08x n=%u u=%u }  CB { v=%u x=%u t=%u }",
  		       callbacks->fid.vid,
  		       callbacks->fid.vnode,
  		       callbacks->fid.unique,
  		       callbacks->version,
  		       callbacks->expiry,
  		       callbacks->type
  		       );
  		afs_break_one_callback(server, &callbacks->fid);
  	}
  
  	_leave("");
  	return;
  }
  
  /*
   * record the callback for breaking
   * - the caller must hold server->cb_lock
   */
  static void afs_do_give_up_callback(struct afs_server *server,
  				    struct afs_vnode *vnode)
  {
  	struct afs_callback *cb;
  
  	_enter("%p,%p", server, vnode);
  
  	cb = &server->cb_break[server->cb_break_head];
  	cb->fid		= vnode->fid;
  	cb->version	= vnode->cb_version;
  	cb->expiry	= vnode->cb_expiry;
  	cb->type	= vnode->cb_type;
  	smp_wmb();
  	server->cb_break_head =
  		(server->cb_break_head + 1) &
  		(ARRAY_SIZE(server->cb_break) - 1);
  
  	/* defer the breaking of callbacks to try and collect as many as
  	 * possible to ship in one operation */
  	switch (atomic_inc_return(&server->cb_break_n)) {
  	case 1 ... AFSCBMAX - 1:
  		queue_delayed_work(afs_callback_update_worker,
  				   &server->cb_break_work, HZ * 2);
  		break;
  	case AFSCBMAX:
  		afs_flush_callback_breaks(server);
  		break;
  	default:
  		break;
  	}
  
  	ASSERT(server->cb_promises.rb_node != NULL);
  	rb_erase(&vnode->cb_promise, &server->cb_promises);
  	vnode->cb_promised = false;
  	_leave("");
  }
  
  /*
   * discard the callback on a deleted item
   */
  void afs_discard_callback_on_delete(struct afs_vnode *vnode)
  {
  	struct afs_server *server = vnode->server;
  
  	_enter("%d", vnode->cb_promised);
  
  	if (!vnode->cb_promised) {
  		_leave(" [not promised]");
  		return;
  	}
  
  	ASSERT(server != NULL);
  
  	spin_lock(&server->cb_lock);
  	if (vnode->cb_promised) {
  		ASSERT(server->cb_promises.rb_node != NULL);
  		rb_erase(&vnode->cb_promise, &server->cb_promises);
  		vnode->cb_promised = false;
  	}
  	spin_unlock(&server->cb_lock);
  	_leave("");
  }
  
  /*
   * give up the callback registered for a vnode on the file server when the
   * inode is being cleared
   */
  void afs_give_up_callback(struct afs_vnode *vnode)
  {
  	struct afs_server *server = vnode->server;
  
  	DECLARE_WAITQUEUE(myself, current);
  
  	_enter("%d", vnode->cb_promised);
  
  	_debug("GIVE UP INODE %p", &vnode->vfs_inode);
  
  	if (!vnode->cb_promised) {
  		_leave(" [not promised]");
  		return;
  	}
  
  	ASSERT(server != NULL);
  
  	spin_lock(&server->cb_lock);
  	if (vnode->cb_promised && afs_breakring_space(server) == 0) {
  		add_wait_queue(&server->cb_break_waitq, &myself);
  		for (;;) {
  			set_current_state(TASK_UNINTERRUPTIBLE);
  			if (!vnode->cb_promised ||
  			    afs_breakring_space(server) != 0)
  				break;
  			spin_unlock(&server->cb_lock);
  			schedule();
  			spin_lock(&server->cb_lock);
  		}
  		remove_wait_queue(&server->cb_break_waitq, &myself);
  		__set_current_state(TASK_RUNNING);
  	}
  
  	/* of course, it's always possible for the server to break this vnode's
  	 * callback first... */
  	if (vnode->cb_promised)
  		afs_do_give_up_callback(server, vnode);
  
  	spin_unlock(&server->cb_lock);
  	_leave("");
  }
  
  /*
   * dispatch a deferred give up callbacks operation
   */
  void afs_dispatch_give_up_callbacks(struct work_struct *work)
  {
  	struct afs_server *server =
  		container_of(work, struct afs_server, cb_break_work.work);
  
  	_enter("");
  
  	/* tell the fileserver to discard the callback promises it has
  	 * - in the event of ENOMEM or some other error, we just forget that we
  	 *   had callbacks entirely, and the server will call us later to break
  	 *   them
  	 */
  	afs_fs_give_up_callbacks(server, &afs_async_call);
  }
  
  /*
   * flush the outstanding callback breaks on a server
   */
  void afs_flush_callback_breaks(struct afs_server *server)
  {
  	mod_delayed_work(afs_callback_update_worker, &server->cb_break_work, 0);
  }
  
  #if 0
  /*
   * update a bunch of callbacks
   */
  static void afs_callback_updater(struct work_struct *work)
  {
  	struct afs_server *server;
  	struct afs_vnode *vnode, *xvnode;
  	time_t now;
  	long timeout;
  	int ret;
  
  	server = container_of(work, struct afs_server, updater);
  
  	_enter("");
  
  	now = get_seconds();
  
  	/* find the first vnode to update */
  	spin_lock(&server->cb_lock);
  	for (;;) {
  		if (RB_EMPTY_ROOT(&server->cb_promises)) {
  			spin_unlock(&server->cb_lock);
  			_leave(" [nothing]");
  			return;
  		}
  
  		vnode = rb_entry(rb_first(&server->cb_promises),
  				 struct afs_vnode, cb_promise);
  		if (atomic_read(&vnode->usage) > 0)
  			break;
  		rb_erase(&vnode->cb_promise, &server->cb_promises);
  		vnode->cb_promised = false;
  	}
  
  	timeout = vnode->update_at - now;
  	if (timeout > 0) {
  		queue_delayed_work(afs_vnode_update_worker,
  				   &afs_vnode_update, timeout * HZ);
  		spin_unlock(&server->cb_lock);
  		_leave(" [nothing]");
  		return;
  	}
  
  	list_del_init(&vnode->update);
  	atomic_inc(&vnode->usage);
  	spin_unlock(&server->cb_lock);
  
  	/* we can now perform the update */
  	_debug("update %s", vnode->vldb.name);
  	vnode->state = AFS_VL_UPDATING;
  	vnode->upd_rej_cnt = 0;
  	vnode->upd_busy_cnt = 0;
  
  	ret = afs_vnode_update_record(vl, &vldb);
  	switch (ret) {
  	case 0:
  		afs_vnode_apply_update(vl, &vldb);
  		vnode->state = AFS_VL_UPDATING;
  		break;
  	case -ENOMEDIUM:
  		vnode->state = AFS_VL_VOLUME_DELETED;
  		break;
  	default:
  		vnode->state = AFS_VL_UNCERTAIN;
  		break;
  	}
  
  	/* and then reschedule */
  	_debug("reschedule");
  	vnode->update_at = get_seconds() + afs_vnode_update_timeout;
  
  	spin_lock(&server->cb_lock);
  
  	if (!list_empty(&server->cb_promises)) {
  		/* next update in 10 minutes, but wait at least 1 second more
  		 * than the newest record already queued so that we don't spam
  		 * the VL server suddenly with lots of requests
  		 */
  		xvnode = list_entry(server->cb_promises.prev,
  				    struct afs_vnode, update);
  		if (vnode->update_at <= xvnode->update_at)
  			vnode->update_at = xvnode->update_at + 1;
  		xvnode = list_entry(server->cb_promises.next,
  				    struct afs_vnode, update);
  		timeout = xvnode->update_at - now;
  		if (timeout < 0)
  			timeout = 0;
  	} else {
  		timeout = afs_vnode_update_timeout;
  	}
  
  	list_add_tail(&vnode->update, &server->cb_promises);
  
  	_debug("timeout %ld", timeout);
  	queue_delayed_work(afs_vnode_update_worker,
  			   &afs_vnode_update, timeout * HZ);
  	spin_unlock(&server->cb_lock);
  	afs_put_vnode(vl);
  }
  #endif
  
  /*
   * initialise the callback update process
   */
  int __init afs_callback_update_init(void)
  {
  	afs_callback_update_worker =
  		create_singlethread_workqueue("kafs_callbackd");
  	return afs_callback_update_worker ? 0 : -ENOMEM;
  }
  
  /*
   * shut down the callback update process
   */
  void afs_callback_update_kill(void)
  {
  	destroy_workqueue(afs_callback_update_worker);
  }