fs/afs/flock.c - kernel/msm-4.9 - Gitiles

 /* 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 <linux/smp_lock.h>
 #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 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)
 {
 	if (!afs_lock_manager) {
 		afs_lock_manager = create_singlethread_workqueue("kafs_lockd");
 		if (!afs_lock_manager)
 			return -ENOMEM;
 	}
 	return 0;
 }

 /*
  * 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);
 }

 /*
  * 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\n",
 			       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\n",
 			       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)
 					list_move_tail(&fl->fl_u.afs.link,
 						       &vnode->granted_locks);
 				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 afs_vnode *vnode = AFS_FS_I(file->f_mapping->host);
 	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;

 	lock_kernel();

 	/* 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 (list_empty(&vnode->pending_locks)) {
 		/* 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->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:
 				goto acquired_server_lock;
 			case -EWOULDBLOCK:
 				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;
 			}
 		}

 		/* if we've already got a readlock on the server and no waiting
 		 * writelocks, then we might be able to instantly grant another
 		 * readlock */
 		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;
 		}
 	}

 	/* 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:
 	unlock_kernel();
 	_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);
 	spin_unlock(&vnode->lock);
 	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;
 	if (posix_test_lock(file, fl) == 0) {
 		/* 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->f_dentry->d_inode);

 	_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 ((vnode->vfs_inode.i_mode & (S_ISGID | S_IXGRP)) == S_ISGID &&
 	    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->f_dentry->d_inode);

 	_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);
 }
	/* 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 <linux/smp_lock.h>
	#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 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)
	{
	if (!afs_lock_manager) {
	afs_lock_manager = create_singlethread_workqueue("kafs_lockd");
	if (!afs_lock_manager)
	return -ENOMEM;
	}
	return 0;
	}

	/*
	* 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);
	}

	/*
	* 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\n",
	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\n",
	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)
	list_move_tail(&fl->fl_u.afs.link,
	&vnode->granted_locks);
	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 afs_vnode *vnode = AFS_FS_I(file->f_mapping->host);
	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;

	lock_kernel();

	/* 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 (list_empty(&vnode->pending_locks)) {
	/* 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->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:
	goto acquired_server_lock;
	case -EWOULDBLOCK:
	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;
	}
	}

	/* if we've already got a readlock on the server and no waiting
	* writelocks, then we might be able to instantly grant another
	* readlock */
	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;
	}
	}

	/* 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:
	unlock_kernel();
	_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);
	spin_unlock(&vnode->lock);
	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;
	if (posix_test_lock(file, fl) == 0) {
	/* 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->f_dentry->d_inode);

	_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 ((vnode->vfs_inode.i_mode & (S_ISGID \| S_IXGRP)) == S_ISGID &&
	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->f_dentry->d_inode);

	_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);
	}