/*
   *  linux/fs/locks.c
   *
   *  Provide support for fcntl()'s F_GETLK, F_SETLK, and F_SETLKW calls.
   *  Doug Evans (dje@spiff.uucp), August 07, 1992
   *
   *  Deadlock detection added.
   *  FIXME: one thing isn't handled yet:
   *	- mandatory locks (requires lots of changes elsewhere)
   *  Kelly Carmichael (kelly@[142.24.8.65]), September 17, 1994.
   *
   *  Miscellaneous edits, and a total rewrite of posix_lock_file() code.
   *  Kai Petzke (wpp@marie.physik.tu-berlin.de), 1994
   *  
   *  Converted file_lock_table to a linked list from an array, which eliminates
   *  the limits on how many active file locks are open.
   *  Chad Page (pageone@netcom.com), November 27, 1994
   * 
   *  Removed dependency on file descriptors. dup()'ed file descriptors now
   *  get the same locks as the original file descriptors, and a close() on
   *  any file descriptor removes ALL the locks on the file for the current
   *  process. Since locks still depend on the process id, locks are inherited
   *  after an exec() but not after a fork(). This agrees with POSIX, and both
   *  BSD and SVR4 practice.
   *  Andy Walker (andy@lysaker.kvaerner.no), February 14, 1995
   *
   *  Scrapped free list which is redundant now that we allocate locks
   *  dynamically with kmalloc()/kfree().
   *  Andy Walker (andy@lysaker.kvaerner.no), February 21, 1995
   *
   *  Implemented two lock personalities - FL_FLOCK and FL_POSIX.
   *
   *  FL_POSIX locks are created with calls to fcntl() and lockf() through the
   *  fcntl() system call. They have the semantics described above.
   *
   *  FL_FLOCK locks are created with calls to flock(), through the flock()
   *  system call, which is new. Old C libraries implement flock() via fcntl()
   *  and will continue to use the old, broken implementation.
   *
   *  FL_FLOCK locks follow the 4.4 BSD flock() semantics. They are associated
   *  with a file pointer (filp). As a result they can be shared by a parent
   *  process and its children after a fork(). They are removed when the last
   *  file descriptor referring to the file pointer is closed (unless explicitly
   *  unlocked). 
   *
   *  FL_FLOCK locks never deadlock, an existing lock is always removed before
   *  upgrading from shared to exclusive (or vice versa). When this happens
   *  any processes blocked by the current lock are woken up and allowed to
   *  run before the new lock is applied.
   *  Andy Walker (andy@lysaker.kvaerner.no), June 09, 1995
   *
   *  Removed some race conditions in flock_lock_file(), marked other possible
   *  races. Just grep for FIXME to see them. 
   *  Dmitry Gorodchanin (pgmdsg@ibi.com), February 09, 1996.
   *
   *  Addressed Dmitry's concerns. Deadlock checking no longer recursive.
   *  Lock allocation changed to GFP_ATOMIC as we can't afford to sleep
   *  once we've checked for blocking and deadlocking.
   *  Andy Walker (andy@lysaker.kvaerner.no), April 03, 1996.
   *
   *  Initial implementation of mandatory locks. SunOS turned out to be
   *  a rotten model, so I implemented the "obvious" semantics.
   *  See 'Documentation/mandatory.txt' for details.
   *  Andy Walker (andy@lysaker.kvaerner.no), April 06, 1996.
   *
   *  Don't allow mandatory locks on mmap()'ed files. Added simple functions to
   *  check if a file has mandatory locks, used by mmap(), open() and creat() to
   *  see if system call should be rejected. Ref. HP-UX/SunOS/Solaris Reference
   *  Manual, Section 2.
   *  Andy Walker (andy@lysaker.kvaerner.no), April 09, 1996.
   *
   *  Tidied up block list handling. Added '/proc/locks' interface.
   *  Andy Walker (andy@lysaker.kvaerner.no), April 24, 1996.
   *
   *  Fixed deadlock condition for pathological code that mixes calls to
   *  flock() and fcntl().
   *  Andy Walker (andy@lysaker.kvaerner.no), April 29, 1996.
   *
   *  Allow only one type of locking scheme (FL_POSIX or FL_FLOCK) to be in use
   *  for a given file at a time. Changed the CONFIG_LOCK_MANDATORY scheme to
   *  guarantee sensible behaviour in the case where file system modules might
   *  be compiled with different options than the kernel itself.
   *  Andy Walker (andy@lysaker.kvaerner.no), May 15, 1996.
   *
   *  Added a couple of missing wake_up() calls. Thanks to Thomas Meckel
   *  (Thomas.Meckel@mni.fh-giessen.de) for spotting this.
   *  Andy Walker (andy@lysaker.kvaerner.no), May 15, 1996.
   *
   *  Changed FL_POSIX locks to use the block list in the same way as FL_FLOCK
   *  locks. Changed process synchronisation to avoid dereferencing locks that
   *  have already been freed.
   *  Andy Walker (andy@lysaker.kvaerner.no), Sep 21, 1996.
   *
   *  Made the block list a circular list to minimise searching in the list.
   *  Andy Walker (andy@lysaker.kvaerner.no), Sep 25, 1996.
   *
   *  Made mandatory locking a mount option. Default is not to allow mandatory
   *  locking.
   *  Andy Walker (andy@lysaker.kvaerner.no), Oct 04, 1996.
   *
   *  Some adaptations for NFS support.
   *  Olaf Kirch (okir@monad.swb.de), Dec 1996,
   *
   *  Fixed /proc/locks interface so that we can't overrun the buffer we are handed.
   *  Andy Walker (andy@lysaker.kvaerner.no), May 12, 1997.
   *
   *  Use slab allocator instead of kmalloc/kfree.
   *  Use generic list implementation from <linux/list.h>.
   *  Sped up posix_locks_deadlock by only considering blocked locks.
   *  Matthew Wilcox <willy@debian.org>, March, 2000.
   *
   *  Leases and LOCK_MAND
   *  Matthew Wilcox <willy@debian.org>, June, 2000.
   *  Stephen Rothwell <sfr@canb.auug.org.au>, June, 2000.
   */
  
  #include <linux/capability.h>
  #include <linux/file.h>

  #include <linux/fdtable.h>

  #include <linux/fs.h>
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/security.h>
  #include <linux/slab.h>

  #include <linux/syscalls.h>
  #include <linux/time.h>

  #include <linux/rcupdate.h>

  #include <linux/pid_namespace.h>

  #include <asm/uaccess.h>
  
  #define IS_POSIX(fl)	(fl->fl_flags & FL_POSIX)
  #define IS_FLOCK(fl)	(fl->fl_flags & FL_FLOCK)
  #define IS_LEASE(fl)	(fl->fl_flags & FL_LEASE)
  
  int leases_enable = 1;
  int lease_break_time = 45;
  
  #define for_each_lock(inode, lockp) \
  	for (lockp = &inode->i_flock; *lockp != NULL; lockp = &(*lockp)->fl_next)

  static LIST_HEAD(file_lock_list);

  static LIST_HEAD(blocked_list);

  static DEFINE_SPINLOCK(file_lock_lock);

  /*
   * Protects the two list heads above, plus the inode->i_flock list

   */
  void lock_flocks(void)
  {

  	spin_lock(&file_lock_lock);

  }
  EXPORT_SYMBOL_GPL(lock_flocks);
  
  void unlock_flocks(void)
  {

  	spin_unlock(&file_lock_lock);

  }
  EXPORT_SYMBOL_GPL(unlock_flocks);

  static struct kmem_cache *filelock_cache __read_mostly;

  static void locks_init_lock_heads(struct file_lock *fl)

  {

  	INIT_LIST_HEAD(&fl->fl_link);
  	INIT_LIST_HEAD(&fl->fl_block);
  	init_waitqueue_head(&fl->fl_wait);

  }

  /* Allocate an empty lock structure. */

  struct file_lock *locks_alloc_lock(void)

  {

  	struct file_lock *fl = kmem_cache_zalloc(filelock_cache, GFP_KERNEL);

  
  	if (fl)

  		locks_init_lock_heads(fl);

  
  	return fl;

  }

  EXPORT_SYMBOL_GPL(locks_alloc_lock);

  void locks_release_private(struct file_lock *fl)

  {
  	if (fl->fl_ops) {
  		if (fl->fl_ops->fl_release_private)
  			fl->fl_ops->fl_release_private(fl);
  		fl->fl_ops = NULL;
  	}
  	if (fl->fl_lmops) {

  		if (fl->fl_lmops->lm_release_private)
  			fl->fl_lmops->lm_release_private(fl);

  		fl->fl_lmops = NULL;
  	}
  
  }

  EXPORT_SYMBOL_GPL(locks_release_private);

  /* Free a lock which is not in use. */

  void locks_free_lock(struct file_lock *fl)

  {

  	BUG_ON(waitqueue_active(&fl->fl_wait));
  	BUG_ON(!list_empty(&fl->fl_block));
  	BUG_ON(!list_empty(&fl->fl_link));

  	locks_release_private(fl);

  	kmem_cache_free(filelock_cache, fl);
  }

  EXPORT_SYMBOL(locks_free_lock);

  
  void locks_init_lock(struct file_lock *fl)
  {

  	memset(fl, 0, sizeof(struct file_lock));
  	locks_init_lock_heads(fl);

  }
  
  EXPORT_SYMBOL(locks_init_lock);

  static void locks_copy_private(struct file_lock *new, struct file_lock *fl)
  {
  	if (fl->fl_ops) {
  		if (fl->fl_ops->fl_copy_lock)
  			fl->fl_ops->fl_copy_lock(new, fl);
  		new->fl_ops = fl->fl_ops;
  	}

  	if (fl->fl_lmops)

  		new->fl_lmops = fl->fl_lmops;

  }

  /*
   * Initialize a new lock from an existing file_lock structure.
   */

  void __locks_copy_lock(struct file_lock *new, const struct file_lock *fl)

  {
  	new->fl_owner = fl->fl_owner;
  	new->fl_pid = fl->fl_pid;

  	new->fl_file = NULL;

  	new->fl_flags = fl->fl_flags;
  	new->fl_type = fl->fl_type;
  	new->fl_start = fl->fl_start;
  	new->fl_end = fl->fl_end;

  	new->fl_ops = NULL;
  	new->fl_lmops = NULL;
  }

  EXPORT_SYMBOL(__locks_copy_lock);

  
  void locks_copy_lock(struct file_lock *new, struct file_lock *fl)
  {
  	locks_release_private(new);
  
  	__locks_copy_lock(new, fl);
  	new->fl_file = fl->fl_file;

  	new->fl_ops = fl->fl_ops;
  	new->fl_lmops = fl->fl_lmops;

  
  	locks_copy_private(new, fl);

  }
  
  EXPORT_SYMBOL(locks_copy_lock);
  
  static inline int flock_translate_cmd(int cmd) {
  	if (cmd & LOCK_MAND)
  		return cmd & (LOCK_MAND | LOCK_RW);
  	switch (cmd) {
  	case LOCK_SH:
  		return F_RDLCK;
  	case LOCK_EX:
  		return F_WRLCK;
  	case LOCK_UN:
  		return F_UNLCK;
  	}
  	return -EINVAL;
  }
  
  /* Fill in a file_lock structure with an appropriate FLOCK lock. */
  static int flock_make_lock(struct file *filp, struct file_lock **lock,
  		unsigned int cmd)
  {
  	struct file_lock *fl;
  	int type = flock_translate_cmd(cmd);
  	if (type < 0)
  		return type;
  	
  	fl = locks_alloc_lock();
  	if (fl == NULL)
  		return -ENOMEM;
  
  	fl->fl_file = filp;
  	fl->fl_pid = current->tgid;
  	fl->fl_flags = FL_FLOCK;
  	fl->fl_type = type;
  	fl->fl_end = OFFSET_MAX;
  	
  	*lock = fl;
  	return 0;
  }
  
  static int assign_type(struct file_lock *fl, int type)
  {
  	switch (type) {
  	case F_RDLCK:
  	case F_WRLCK:
  	case F_UNLCK:
  		fl->fl_type = type;
  		break;
  	default:
  		return -EINVAL;
  	}
  	return 0;
  }
  
  /* Verify a "struct flock" and copy it to a "struct file_lock" as a POSIX
   * style lock.
   */
  static int flock_to_posix_lock(struct file *filp, struct file_lock *fl,
  			       struct flock *l)
  {
  	off_t start, end;
  
  	switch (l->l_whence) {

  	case SEEK_SET:

  		start = 0;
  		break;

  	case SEEK_CUR:

  		start = filp->f_pos;
  		break;

  	case SEEK_END:

  		start = i_size_read(filp->f_path.dentry->d_inode);

  		break;
  	default:
  		return -EINVAL;
  	}
  
  	/* POSIX-1996 leaves the case l->l_len < 0 undefined;
  	   POSIX-2001 defines it. */
  	start += l->l_start;

  	if (start < 0)
  		return -EINVAL;
  	fl->fl_end = OFFSET_MAX;
  	if (l->l_len > 0) {
  		end = start + l->l_len - 1;
  		fl->fl_end = end;
  	} else if (l->l_len < 0) {

  		end = start - 1;

  		fl->fl_end = end;

  		start += l->l_len;

  		if (start < 0)
  			return -EINVAL;

  	}

  	fl->fl_start = start;	/* we record the absolute position */

  	if (fl->fl_end < fl->fl_start)
  		return -EOVERFLOW;

  	
  	fl->fl_owner = current->files;
  	fl->fl_pid = current->tgid;
  	fl->fl_file = filp;
  	fl->fl_flags = FL_POSIX;
  	fl->fl_ops = NULL;
  	fl->fl_lmops = NULL;
  
  	return assign_type(fl, l->l_type);
  }
  
  #if BITS_PER_LONG == 32
  static int flock64_to_posix_lock(struct file *filp, struct file_lock *fl,
  				 struct flock64 *l)
  {
  	loff_t start;
  
  	switch (l->l_whence) {

  	case SEEK_SET:

  		start = 0;
  		break;

  	case SEEK_CUR:

  		start = filp->f_pos;
  		break;

  	case SEEK_END:

  		start = i_size_read(filp->f_path.dentry->d_inode);

  		break;
  	default:
  		return -EINVAL;
  	}

  	start += l->l_start;
  	if (start < 0)

  		return -EINVAL;

  	fl->fl_end = OFFSET_MAX;
  	if (l->l_len > 0) {
  		fl->fl_end = start + l->l_len - 1;
  	} else if (l->l_len < 0) {
  		fl->fl_end = start - 1;
  		start += l->l_len;
  		if (start < 0)
  			return -EINVAL;
  	}

  	fl->fl_start = start;	/* we record the absolute position */

  	if (fl->fl_end < fl->fl_start)
  		return -EOVERFLOW;

  	
  	fl->fl_owner = current->files;
  	fl->fl_pid = current->tgid;
  	fl->fl_file = filp;
  	fl->fl_flags = FL_POSIX;
  	fl->fl_ops = NULL;
  	fl->fl_lmops = NULL;

  	return assign_type(fl, l->l_type);

  }
  #endif
  
  /* default lease lock manager operations */
  static void lease_break_callback(struct file_lock *fl)
  {
  	kill_fasync(&fl->fl_fasync, SIGIO, POLL_MSG);
  }
  
  static void lease_release_private_callback(struct file_lock *fl)
  {
  	if (!fl->fl_file)
  		return;
  
  	f_delown(fl->fl_file);
  	fl->fl_file->f_owner.signum = 0;
  }

  static const struct lock_manager_operations lease_manager_ops = {

  	.lm_break = lease_break_callback,
  	.lm_release_private = lease_release_private_callback,
  	.lm_change = lease_modify,

  };
  
  /*
   * Initialize a lease, use the default lock manager operations
   */
  static int lease_init(struct file *filp, int type, struct file_lock *fl)
   {

  	if (assign_type(fl, type) != 0)
  		return -EINVAL;

  	fl->fl_owner = current->files;
  	fl->fl_pid = current->tgid;
  
  	fl->fl_file = filp;
  	fl->fl_flags = FL_LEASE;

  	fl->fl_start = 0;
  	fl->fl_end = OFFSET_MAX;
  	fl->fl_ops = NULL;
  	fl->fl_lmops = &lease_manager_ops;
  	return 0;
  }
  
  /* Allocate a file_lock initialised to this type of lease */

  static struct file_lock *lease_alloc(struct file *filp, int type)

  {
  	struct file_lock *fl = locks_alloc_lock();

  	int error = -ENOMEM;

  
  	if (fl == NULL)

  		return ERR_PTR(error);

  
  	error = lease_init(filp, type, fl);

  	if (error) {
  		locks_free_lock(fl);

  		return ERR_PTR(error);

  	}

  	return fl;

  }
  
  /* Check if two locks overlap each other.
   */
  static inline int locks_overlap(struct file_lock *fl1, struct file_lock *fl2)
  {
  	return ((fl1->fl_end >= fl2->fl_start) &&
  		(fl2->fl_end >= fl1->fl_start));
  }
  
  /*
   * Check whether two locks have the same owner.
   */

  static int posix_same_owner(struct file_lock *fl1, struct file_lock *fl2)

  {

  	if (fl1->fl_lmops && fl1->fl_lmops->lm_compare_owner)

  		return fl2->fl_lmops == fl1->fl_lmops &&

  			fl1->fl_lmops->lm_compare_owner(fl1, fl2);

  	return fl1->fl_owner == fl2->fl_owner;
  }
  
  /* Remove waiter from blocker's block list.
   * When blocker ends up pointing to itself then the list is empty.
   */

  static void __locks_delete_block(struct file_lock *waiter)

  {
  	list_del_init(&waiter->fl_block);
  	list_del_init(&waiter->fl_link);
  	waiter->fl_next = NULL;
  }
  
  /*
   */
  static void locks_delete_block(struct file_lock *waiter)
  {

  	lock_flocks();

  	__locks_delete_block(waiter);

  	unlock_flocks();

  }
  
  /* Insert waiter into blocker's block list.
   * We use a circular list so that processes can be easily woken up in
   * the order they blocked. The documentation doesn't require this but
   * it seems like the reasonable thing to do.
   */
  static void locks_insert_block(struct file_lock *blocker, 
  			       struct file_lock *waiter)
  {

  	BUG_ON(!list_empty(&waiter->fl_block));

  	list_add_tail(&waiter->fl_block, &blocker->fl_block);
  	waiter->fl_next = blocker;
  	if (IS_POSIX(blocker))
  		list_add(&waiter->fl_link, &blocked_list);
  }
  
  /* Wake up processes blocked waiting for blocker.
   * If told to wait then schedule the processes until the block list
   * is empty, otherwise empty the block list ourselves.
   */
  static void locks_wake_up_blocks(struct file_lock *blocker)
  {
  	while (!list_empty(&blocker->fl_block)) {

  		struct file_lock *waiter;
  
  		waiter = list_first_entry(&blocker->fl_block,

  				struct file_lock, fl_block);
  		__locks_delete_block(waiter);

  		if (waiter->fl_lmops && waiter->fl_lmops->lm_notify)
  			waiter->fl_lmops->lm_notify(waiter);

  		else
  			wake_up(&waiter->fl_wait);
  	}
  }
  
  /* Insert file lock fl into an inode's lock list at the position indicated
   * by pos. At the same time add the lock to the global file lock list.
   */
  static void locks_insert_lock(struct file_lock **pos, struct file_lock *fl)
  {
  	list_add(&fl->fl_link, &file_lock_list);

  	fl->fl_nspid = get_pid(task_tgid(current));

  	/* insert into file's list */
  	fl->fl_next = *pos;
  	*pos = fl;

  }
  
  /*
   * Delete a lock and then free it.
   * Wake up processes that are blocked waiting for this lock,
   * notify the FS that the lock has been cleared and
   * finally free the lock.
   */
  static void locks_delete_lock(struct file_lock **thisfl_p)
  {
  	struct file_lock *fl = *thisfl_p;
  
  	*thisfl_p = fl->fl_next;
  	fl->fl_next = NULL;
  	list_del_init(&fl->fl_link);
  
  	fasync_helper(0, fl->fl_file, 0, &fl->fl_fasync);
  	if (fl->fl_fasync != NULL) {
  		printk(KERN_ERR "locks_delete_lock: fasync == %p
  ", fl->fl_fasync);
  		fl->fl_fasync = NULL;
  	}

  	if (fl->fl_nspid) {
  		put_pid(fl->fl_nspid);
  		fl->fl_nspid = NULL;
  	}

  	locks_wake_up_blocks(fl);
  	locks_free_lock(fl);
  }
  
  /* Determine if lock sys_fl blocks lock caller_fl. Common functionality
   * checks for shared/exclusive status of overlapping locks.
   */
  static int locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
  {
  	if (sys_fl->fl_type == F_WRLCK)
  		return 1;
  	if (caller_fl->fl_type == F_WRLCK)
  		return 1;
  	return 0;
  }
  
  /* Determine if lock sys_fl blocks lock caller_fl. POSIX specific
   * checking before calling the locks_conflict().
   */
  static int posix_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
  {
  	/* POSIX locks owned by the same process do not conflict with
  	 * each other.
  	 */
  	if (!IS_POSIX(sys_fl) || posix_same_owner(caller_fl, sys_fl))
  		return (0);
  
  	/* Check whether they overlap */
  	if (!locks_overlap(caller_fl, sys_fl))
  		return 0;
  
  	return (locks_conflict(caller_fl, sys_fl));
  }
  
  /* Determine if lock sys_fl blocks lock caller_fl. FLOCK specific
   * checking before calling the locks_conflict().
   */
  static int flock_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
  {
  	/* FLOCK locks referring to the same filp do not conflict with
  	 * each other.
  	 */
  	if (!IS_FLOCK(sys_fl) || (caller_fl->fl_file == sys_fl->fl_file))
  		return (0);
  	if ((caller_fl->fl_type & LOCK_MAND) || (sys_fl->fl_type & LOCK_MAND))
  		return 0;
  
  	return (locks_conflict(caller_fl, sys_fl));
  }

  void

  posix_test_lock(struct file *filp, struct file_lock *fl)

  {
  	struct file_lock *cfl;

  	lock_flocks();

  	for (cfl = filp->f_path.dentry->d_inode->i_flock; cfl; cfl = cfl->fl_next) {

  		if (!IS_POSIX(cfl))
  			continue;

  		if (posix_locks_conflict(fl, cfl))

  			break;
  	}

  	if (cfl) {

  		__locks_copy_lock(fl, cfl);

  		if (cfl->fl_nspid)

  			fl->fl_pid = pid_vnr(cfl->fl_nspid);

  	} else

  		fl->fl_type = F_UNLCK;

  	unlock_flocks();

  	return;

  }

  EXPORT_SYMBOL(posix_test_lock);

  /*
   * Deadlock detection:
   *
   * We attempt to detect deadlocks that are due purely to posix file
   * locks.

   *

   * We assume that a task can be waiting for at most one lock at a time.
   * So for any acquired lock, the process holding that lock may be
   * waiting on at most one other lock.  That lock in turns may be held by
   * someone waiting for at most one other lock.  Given a requested lock
   * caller_fl which is about to wait for a conflicting lock block_fl, we
   * follow this chain of waiters to ensure we are not about to create a
   * cycle.

   *

   * Since we do this before we ever put a process to sleep on a lock, we
   * are ensured that there is never a cycle; that is what guarantees that
   * the while() loop in posix_locks_deadlock() eventually completes.

   *

   * Note: the above assumption may not be true when handling lock
   * requests from a broken NFS client. It may also fail in the presence
   * of tasks (such as posix threads) sharing the same open file table.
   *
   * To handle those cases, we just bail out after a few iterations.

   */

  
  #define MAX_DEADLK_ITERATIONS 10

  /* Find a lock that the owner of the given block_fl is blocking on. */
  static struct file_lock *what_owner_is_waiting_for(struct file_lock *block_fl)
  {
  	struct file_lock *fl;
  
  	list_for_each_entry(fl, &blocked_list, fl_link) {
  		if (posix_same_owner(fl, block_fl))
  			return fl->fl_next;
  	}
  	return NULL;
  }

  static int posix_locks_deadlock(struct file_lock *caller_fl,

  				struct file_lock *block_fl)
  {

  	int i = 0;

  	while ((block_fl = what_owner_is_waiting_for(block_fl))) {
  		if (i++ > MAX_DEADLK_ITERATIONS)
  			return 0;
  		if (posix_same_owner(caller_fl, block_fl))
  			return 1;

  	}
  	return 0;
  }

  /* Try to create a FLOCK lock on filp. We always insert new FLOCK locks

   * after any leases, but before any posix locks.

   *
   * Note that if called with an FL_EXISTS argument, the caller may determine
   * whether or not a lock was successfully freed by testing the return
   * value for -ENOENT.

   */

  static int flock_lock_file(struct file *filp, struct file_lock *request)

  {

  	struct file_lock *new_fl = NULL;

  	struct file_lock **before;

  	struct inode * inode = filp->f_path.dentry->d_inode;

  	int error = 0;
  	int found = 0;

  	if (!(request->fl_flags & FL_ACCESS) && (request->fl_type != F_UNLCK)) {

  		new_fl = locks_alloc_lock();

  		if (!new_fl)
  			return -ENOMEM;

  	}

  	lock_flocks();
  	if (request->fl_flags & FL_ACCESS)
  		goto find_conflict;

  	for_each_lock(inode, before) {
  		struct file_lock *fl = *before;
  		if (IS_POSIX(fl))
  			break;
  		if (IS_LEASE(fl))
  			continue;
  		if (filp != fl->fl_file)
  			continue;

  		if (request->fl_type == fl->fl_type)

  			goto out;
  		found = 1;
  		locks_delete_lock(before);
  		break;
  	}

  	if (request->fl_type == F_UNLCK) {
  		if ((request->fl_flags & FL_EXISTS) && !found)
  			error = -ENOENT;

  		goto out;

  	}

  
  	/*
  	 * If a higher-priority process was blocked on the old file lock,
  	 * give it the opportunity to lock the file.
  	 */

  	if (found) {
  		unlock_flocks();

  		cond_resched();

  		lock_flocks();
  	}

  find_conflict:

  	for_each_lock(inode, before) {
  		struct file_lock *fl = *before;
  		if (IS_POSIX(fl))
  			break;
  		if (IS_LEASE(fl))
  			continue;

  		if (!flock_locks_conflict(request, fl))

  			continue;
  		error = -EAGAIN;

  		if (!(request->fl_flags & FL_SLEEP))
  			goto out;
  		error = FILE_LOCK_DEFERRED;
  		locks_insert_block(fl, request);

  		goto out;
  	}

  	if (request->fl_flags & FL_ACCESS)
  		goto out;

  	locks_copy_lock(new_fl, request);

  	locks_insert_lock(before, new_fl);

  	new_fl = NULL;

  	error = 0;

  
  out:

  	unlock_flocks();

  	if (new_fl)
  		locks_free_lock(new_fl);

  	return error;
  }

  static int __posix_lock_file(struct inode *inode, struct file_lock *request, struct file_lock *conflock)

  {
  	struct file_lock *fl;

  	struct file_lock *new_fl = NULL;
  	struct file_lock *new_fl2 = NULL;

  	struct file_lock *left = NULL;
  	struct file_lock *right = NULL;
  	struct file_lock **before;
  	int error, added = 0;
  
  	/*
  	 * We may need two file_lock structures for this operation,
  	 * so we get them in advance to avoid races.

  	 *
  	 * In some cases we can be sure, that no new locks will be needed

  	 */

  	if (!(request->fl_flags & FL_ACCESS) &&
  	    (request->fl_type != F_UNLCK ||
  	     request->fl_start != 0 || request->fl_end != OFFSET_MAX)) {
  		new_fl = locks_alloc_lock();
  		new_fl2 = locks_alloc_lock();
  	}

  	lock_flocks();

  	if (request->fl_type != F_UNLCK) {
  		for_each_lock(inode, before) {

  			fl = *before;

  			if (!IS_POSIX(fl))
  				continue;
  			if (!posix_locks_conflict(request, fl))
  				continue;

  			if (conflock)

  				__locks_copy_lock(conflock, fl);

  			error = -EAGAIN;
  			if (!(request->fl_flags & FL_SLEEP))
  				goto out;
  			error = -EDEADLK;
  			if (posix_locks_deadlock(request, fl))
  				goto out;

  			error = FILE_LOCK_DEFERRED;

  			locks_insert_block(fl, request);
  			goto out;
    		}
    	}
  
  	/* If we're just looking for a conflict, we're done. */
  	error = 0;
  	if (request->fl_flags & FL_ACCESS)
  		goto out;

  	/*

  	 * Find the first old lock with the same owner as the new lock.
  	 */
  	
  	before = &inode->i_flock;
  
  	/* First skip locks owned by other processes.  */
  	while ((fl = *before) && (!IS_POSIX(fl) ||
  				  !posix_same_owner(request, fl))) {
  		before = &fl->fl_next;
  	}
  
  	/* Process locks with this owner.  */
  	while ((fl = *before) && posix_same_owner(request, fl)) {
  		/* Detect adjacent or overlapping regions (if same lock type)
  		 */
  		if (request->fl_type == fl->fl_type) {

  			/* In all comparisons of start vs end, use
  			 * "start - 1" rather than "end + 1". If end
  			 * is OFFSET_MAX, end + 1 will become negative.
  			 */

  			if (fl->fl_end < request->fl_start - 1)
  				goto next_lock;
  			/* If the next lock in the list has entirely bigger
  			 * addresses than the new one, insert the lock here.
  			 */

  			if (fl->fl_start - 1 > request->fl_end)

  				break;
  
  			/* If we come here, the new and old lock are of the
  			 * same type and adjacent or overlapping. Make one
  			 * lock yielding from the lower start address of both
  			 * locks to the higher end address.
  			 */
  			if (fl->fl_start > request->fl_start)
  				fl->fl_start = request->fl_start;
  			else
  				request->fl_start = fl->fl_start;
  			if (fl->fl_end < request->fl_end)
  				fl->fl_end = request->fl_end;
  			else
  				request->fl_end = fl->fl_end;
  			if (added) {
  				locks_delete_lock(before);
  				continue;
  			}
  			request = fl;
  			added = 1;
  		}
  		else {
  			/* Processing for different lock types is a bit
  			 * more complex.
  			 */
  			if (fl->fl_end < request->fl_start)
  				goto next_lock;
  			if (fl->fl_start > request->fl_end)
  				break;
  			if (request->fl_type == F_UNLCK)
  				added = 1;
  			if (fl->fl_start < request->fl_start)
  				left = fl;
  			/* If the next lock in the list has a higher end
  			 * address than the new one, insert the new one here.
  			 */
  			if (fl->fl_end > request->fl_end) {
  				right = fl;
  				break;
  			}
  			if (fl->fl_start >= request->fl_start) {
  				/* The new lock completely replaces an old
  				 * one (This may happen several times).
  				 */
  				if (added) {
  					locks_delete_lock(before);
  					continue;
  				}
  				/* Replace the old lock with the new one.
  				 * Wake up anybody waiting for the old one,
  				 * as the change in lock type might satisfy
  				 * their needs.
  				 */
  				locks_wake_up_blocks(fl);
  				fl->fl_start = request->fl_start;
  				fl->fl_end = request->fl_end;
  				fl->fl_type = request->fl_type;

  				locks_release_private(fl);
  				locks_copy_private(fl, request);

  				request = fl;
  				added = 1;
  			}
  		}
  		/* Go on to next lock.
  		 */
  	next_lock:
  		before = &fl->fl_next;
  	}

  	/*
  	 * The above code only modifies existing locks in case of
  	 * merging or replacing.  If new lock(s) need to be inserted
  	 * all modifications are done bellow this, so it's safe yet to
  	 * bail out.
  	 */
  	error = -ENOLCK; /* "no luck" */
  	if (right && left == right && !new_fl2)
  		goto out;

  	error = 0;
  	if (!added) {

  		if (request->fl_type == F_UNLCK) {
  			if (request->fl_flags & FL_EXISTS)
  				error = -ENOENT;

  			goto out;

  		}

  
  		if (!new_fl) {
  			error = -ENOLCK;
  			goto out;
  		}

  		locks_copy_lock(new_fl, request);
  		locks_insert_lock(before, new_fl);
  		new_fl = NULL;
  	}
  	if (right) {
  		if (left == right) {
  			/* The new lock breaks the old one in two pieces,
  			 * so we have to use the second new lock.
  			 */
  			left = new_fl2;
  			new_fl2 = NULL;
  			locks_copy_lock(left, right);
  			locks_insert_lock(before, left);
  		}
  		right->fl_start = request->fl_end + 1;
  		locks_wake_up_blocks(right);
  	}
  	if (left) {
  		left->fl_end = request->fl_start - 1;
  		locks_wake_up_blocks(left);
  	}
   out:

  	unlock_flocks();

  	/*
  	 * Free any unused locks.
  	 */
  	if (new_fl)
  		locks_free_lock(new_fl);
  	if (new_fl2)
  		locks_free_lock(new_fl2);
  	return error;
  }
  
  /**
   * posix_lock_file - Apply a POSIX-style lock to a file
   * @filp: The file to apply the lock to
   * @fl: The lock to be applied

   * @conflock: Place to return a copy of the conflicting lock, if found.

   *
   * Add a POSIX style lock to a file.
   * We merge adjacent & overlapping locks whenever possible.
   * POSIX locks are sorted by owner task, then by starting address

   *
   * Note that if called with an FL_EXISTS argument, the caller may determine
   * whether or not a lock was successfully freed by testing the return
   * value for -ENOENT.

   */

  int posix_lock_file(struct file *filp, struct file_lock *fl,

  			struct file_lock *conflock)
  {

  	return __posix_lock_file(filp->f_path.dentry->d_inode, fl, conflock);

  }

  EXPORT_SYMBOL(posix_lock_file);

  
  /**
   * posix_lock_file_wait - Apply a POSIX-style lock to a file
   * @filp: The file to apply the lock to
   * @fl: The lock to be applied
   *
   * Add a POSIX style lock to a file.
   * We merge adjacent & overlapping locks whenever possible.
   * POSIX locks are sorted by owner task, then by starting address
   */
  int posix_lock_file_wait(struct file *filp, struct file_lock *fl)
  {
  	int error;
  	might_sleep ();
  	for (;;) {

  		error = posix_lock_file(filp, fl, NULL);

  		if (error != FILE_LOCK_DEFERRED)

  			break;
  		error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
  		if (!error)
  			continue;
  
  		locks_delete_block(fl);
  		break;
  	}
  	return error;
  }
  EXPORT_SYMBOL(posix_lock_file_wait);
  
  /**
   * locks_mandatory_locked - Check for an active lock
   * @inode: the file to check
   *
   * Searches the inode's list of locks to find any POSIX locks which conflict.
   * This function is called from locks_verify_locked() only.
   */
  int locks_mandatory_locked(struct inode *inode)
  {
  	fl_owner_t owner = current->files;
  	struct file_lock *fl;
  
  	/*
  	 * Search the lock list for this inode for any POSIX locks.
  	 */

  	lock_flocks();

  	for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
  		if (!IS_POSIX(fl))
  			continue;
  		if (fl->fl_owner != owner)
  			break;
  	}

  	unlock_flocks();

  	return fl ? -EAGAIN : 0;
  }
  
  /**
   * locks_mandatory_area - Check for a conflicting lock
   * @read_write: %FLOCK_VERIFY_WRITE for exclusive access, %FLOCK_VERIFY_READ
   *		for shared
   * @inode:      the file to check
   * @filp:       how the file was opened (if it was)
   * @offset:     start of area to check
   * @count:      length of area to check
   *
   * Searches the inode's list of locks to find any POSIX locks which conflict.
   * This function is called from rw_verify_area() and
   * locks_verify_truncate().
   */
  int locks_mandatory_area(int read_write, struct inode *inode,
  			 struct file *filp, loff_t offset,
  			 size_t count)
  {
  	struct file_lock fl;
  	int error;
  
  	locks_init_lock(&fl);
  	fl.fl_owner = current->files;
  	fl.fl_pid = current->tgid;
  	fl.fl_file = filp;
  	fl.fl_flags = FL_POSIX | FL_ACCESS;
  	if (filp && !(filp->f_flags & O_NONBLOCK))
  		fl.fl_flags |= FL_SLEEP;
  	fl.fl_type = (read_write == FLOCK_VERIFY_WRITE) ? F_WRLCK : F_RDLCK;
  	fl.fl_start = offset;
  	fl.fl_end = offset + count - 1;
  
  	for (;;) {

  		error = __posix_lock_file(inode, &fl, NULL);

  		if (error != FILE_LOCK_DEFERRED)

  			break;
  		error = wait_event_interruptible(fl.fl_wait, !fl.fl_next);
  		if (!error) {
  			/*
  			 * If we've been sleeping someone might have
  			 * changed the permissions behind our back.
  			 */

  			if (__mandatory_lock(inode))

  				continue;
  		}
  
  		locks_delete_block(&fl);
  		break;
  	}
  
  	return error;
  }
  
  EXPORT_SYMBOL(locks_mandatory_area);
  
  /* We already had a lease on this file; just change its type */
  int lease_modify(struct file_lock **before, int arg)
  {
  	struct file_lock *fl = *before;
  	int error = assign_type(fl, arg);
  
  	if (error)
  		return error;
  	locks_wake_up_blocks(fl);
  	if (arg == F_UNLCK)
  		locks_delete_lock(before);
  	return 0;
  }
  
  EXPORT_SYMBOL(lease_modify);
  
  static void time_out_leases(struct inode *inode)
  {
  	struct file_lock **before;
  	struct file_lock *fl;
  
  	before = &inode->i_flock;
  	while ((fl = *before) && IS_LEASE(fl) && (fl->fl_type & F_INPROGRESS)) {
  		if ((fl->fl_break_time == 0)
  				|| time_before(jiffies, fl->fl_break_time)) {
  			before = &fl->fl_next;
  			continue;
  		}

  		lease_modify(before, fl->fl_type & ~F_INPROGRESS);
  		if (fl == *before)	/* lease_modify may have freed fl */
  			before = &fl->fl_next;
  	}
  }
  
  /**
   *	__break_lease	-	revoke all outstanding leases on file
   *	@inode: the inode of the file to return
   *	@mode: the open mode (read or write)
   *

   *	break_lease (inlined for speed) has checked there already is at least
   *	some kind of lock (maybe a lease) on this file.  Leases are broken on
   *	a call to open() or truncate().  This function can sleep unless you

   *	specified %O_NONBLOCK to your open().
   */
  int __break_lease(struct inode *inode, unsigned int mode)
  {
  	int error = 0, future;
  	struct file_lock *new_fl, *flock;
  	struct file_lock *fl;

  	unsigned long break_time;
  	int i_have_this_lease = 0;

  	int want_write = (mode & O_ACCMODE) != O_RDONLY;

  	new_fl = lease_alloc(NULL, want_write ? F_WRLCK : F_RDLCK);

  	lock_flocks();

  
  	time_out_leases(inode);
  
  	flock = inode->i_flock;
  	if ((flock == NULL) || !IS_LEASE(flock))
  		goto out;
  
  	for (fl = flock; fl && IS_LEASE(fl); fl = fl->fl_next)
  		if (fl->fl_owner == current->files)
  			i_have_this_lease = 1;

  	if (want_write) {

  		/* If we want write access, we have to revoke any lease. */
  		future = F_UNLCK | F_INPROGRESS;
  	} else if (flock->fl_type & F_INPROGRESS) {
  		/* If the lease is already being broken, we just leave it */
  		future = flock->fl_type;
  	} else if (flock->fl_type & F_WRLCK) {
  		/* Downgrade the exclusive lease to a read-only lease. */
  		future = F_RDLCK | F_INPROGRESS;
  	} else {
  		/* the existing lease was read-only, so we can read too. */
  		goto out;
  	}

  	if (IS_ERR(new_fl) && !i_have_this_lease
  			&& ((mode & O_NONBLOCK) == 0)) {
  		error = PTR_ERR(new_fl);

  		goto out;
  	}
  
  	break_time = 0;
  	if (lease_break_time > 0) {
  		break_time = jiffies + lease_break_time * HZ;
  		if (break_time == 0)
  			break_time++;	/* so that 0 means no break time */
  	}
  
  	for (fl = flock; fl && IS_LEASE(fl); fl = fl->fl_next) {
  		if (fl->fl_type != future) {
  			fl->fl_type = future;
  			fl->fl_break_time = break_time;
  			/* lease must have lmops break callback */

  			fl->fl_lmops->lm_break(fl);

  		}
  	}
  
  	if (i_have_this_lease || (mode & O_NONBLOCK)) {
  		error = -EWOULDBLOCK;
  		goto out;
  	}
  
  restart:
  	break_time = flock->fl_break_time;
  	if (break_time != 0) {
  		break_time -= jiffies;
  		if (break_time == 0)
  			break_time++;
  	}

  	locks_insert_block(flock, new_fl);

  	unlock_flocks();

  	error = wait_event_interruptible_timeout(new_fl->fl_wait,
  						!new_fl->fl_next, break_time);

  	lock_flocks();

  	__locks_delete_block(new_fl);

  	if (error >= 0) {
  		if (error == 0)
  			time_out_leases(inode);
  		/* Wait for the next lease that has not been broken yet */
  		for (flock = inode->i_flock; flock && IS_LEASE(flock);
  				flock = flock->fl_next) {
  			if (flock->fl_type & F_INPROGRESS)
  				goto restart;
  		}
  		error = 0;
  	}
  
  out:

  	unlock_flocks();

  	if (!IS_ERR(new_fl))

  		locks_free_lock(new_fl);
  	return error;
  }
  
  EXPORT_SYMBOL(__break_lease);
  
  /**

   *	lease_get_mtime - get the last modified time of an inode

   *	@inode: the inode
   *      @time:  pointer to a timespec which will contain the last modified time
   *
   * This is to force NFS clients to flush their caches for files with
   * exclusive leases.  The justification is that if someone has an

   * exclusive lease, then they could be modifying it.

   */
  void lease_get_mtime(struct inode *inode, struct timespec *time)
  {
  	struct file_lock *flock = inode->i_flock;
  	if (flock && IS_LEASE(flock) && (flock->fl_type & F_WRLCK))
  		*time = current_fs_time(inode->i_sb);
  	else
  		*time = inode->i_mtime;
  }
  
  EXPORT_SYMBOL(lease_get_mtime);
  
  /**
   *	fcntl_getlease - Enquire what lease is currently active
   *	@filp: the file
   *
   *	The value returned by this function will be one of
   *	(if no lease break is pending):
   *
   *	%F_RDLCK to indicate a shared lease is held.
   *
   *	%F_WRLCK to indicate an exclusive lease is held.
   *
   *	%F_UNLCK to indicate no lease is held.
   *
   *	(if a lease break is pending):
   *
   *	%F_RDLCK to indicate an exclusive lease needs to be
   *		changed to a shared lease (or removed).
   *
   *	%F_UNLCK to indicate the lease needs to be removed.
   *
   *	XXX: sfr & willy disagree over whether F_INPROGRESS
   *	should be returned to userspace.
   */
  int fcntl_getlease(struct file *filp)
  {
  	struct file_lock *fl;
  	int type = F_UNLCK;

  	lock_flocks();

  	time_out_leases(filp->f_path.dentry->d_inode);
  	for (fl = filp->f_path.dentry->d_inode->i_flock; fl && IS_LEASE(fl);

  			fl = fl->fl_next) {
  		if (fl->fl_file == filp) {
  			type = fl->fl_type & ~F_INPROGRESS;
  			break;
  		}
  	}

  	unlock_flocks();

  	return type;
  }
  
  /**

   *	generic_setlease	-	sets a lease on an open file

   *	@filp: file pointer
   *	@arg: type of lease to obtain
   *	@flp: input - file_lock to use, output - file_lock inserted
   *

   *	The (input) flp->fl_lmops->lm_break function is required

   *	by break_lease().
   *

   *	Called with file_lock_lock held.

   */

  int generic_setlease(struct file *filp, long arg, struct file_lock **flp)

  {

  	struct file_lock *fl, **before, **my_before = NULL, *lease;

  	struct dentry *dentry = filp->f_path.dentry;

  	struct inode *inode = dentry->d_inode;
  	int error, rdlease_count = 0, wrlease_count = 0;

  	lease = *flp;
  
  	error = -EACCES;

  	if ((current_fsuid() != inode->i_uid) && !capable(CAP_LEASE))

  		goto out;
  	error = -EINVAL;

  	if (!S_ISREG(inode->i_mode))

  		goto out;

  	error = security_file_lock(filp, arg);
  	if (error)

  		goto out;

  	time_out_leases(inode);

  	BUG_ON(!(*flp)->fl_lmops->lm_break);

  	if (arg != F_UNLCK) {
  		error = -EAGAIN;
  		if ((arg == F_RDLCK) && (atomic_read(&inode->i_writecount) > 0))
  			goto out;
  		if ((arg == F_WRLCK)

  		    && ((dentry->d_count > 1)

  			|| (atomic_read(&inode->i_count) > 1)))
  			goto out;

  	}

  	/*
  	 * At this point, we know that if there is an exclusive
  	 * lease on this file, then we hold it on this filp
  	 * (otherwise our open of this file would have blocked).
  	 * And if we are trying to acquire an exclusive lease,
  	 * then the file is not open by anyone (including us)
  	 * except for this filp.
  	 */
  	for (before = &inode->i_flock;
  			((fl = *before) != NULL) && IS_LEASE(fl);
  			before = &fl->fl_next) {

  		if (fl->fl_file == filp)

  			my_before = before;
  		else if (fl->fl_type == (F_INPROGRESS | F_UNLCK))
  			/*
  			 * Someone is in the process of opening this
  			 * file for writing so we may not take an
  			 * exclusive lease on it.
  			 */
  			wrlease_count++;
  		else
  			rdlease_count++;
  	}

  	error = -EAGAIN;

  	if ((arg == F_RDLCK && (wrlease_count > 0)) ||
  	    (arg == F_WRLCK && ((rdlease_count + wrlease_count) > 0)))
  		goto out;
  
  	if (my_before != NULL) {

  		error = lease->fl_lmops->lm_change(my_before, arg);

  		if (!error)
  			*flp = *my_before;

  		goto out;
  	}

  	if (arg == F_UNLCK)
  		goto out;
  
  	error = -EINVAL;
  	if (!leases_enable)
  		goto out;

  	locks_insert_lock(before, lease);

  	return 0;

  out:
  	return error;
  }

  EXPORT_SYMBOL(generic_setlease);

  static int __vfs_setlease(struct file *filp, long arg, struct file_lock **lease)
  {
  	if (filp->f_op && filp->f_op->setlease)
  		return filp->f_op->setlease(filp, arg, lease);
  	else
  		return generic_setlease(filp, arg, lease);
  }
  
  /**

   *	vfs_setlease        -       sets a lease on an open file

   *	@filp: file pointer
   *	@arg: type of lease to obtain
   *	@lease: file_lock to use
   *
   *	Call this to establish a lease on the file.

   *	The (*lease)->fl_lmops->lm_break operation must be set; if not,

   *	break_lease will oops!
   *
   *	This will call the filesystem's setlease file method, if
   *	defined.  Note that there is no getlease method; instead, the
   *	filesystem setlease method should call back to setlease() to
   *	add a lease to the inode's lease list, where fcntl_getlease() can
   *	find it.  Since fcntl_getlease() only reports whether the current
   *	task holds a lease, a cluster filesystem need only do this for
   *	leases held by processes on this node.
   *
   *	There is also no break_lease method; filesystems that

   *	handle their own leases should break leases themselves from the

   *	filesystem's open, create, and (on truncate) setattr methods.
   *
   *	Warning: the only current setlease methods exist only to disable
   *	leases in certain cases.  More vfs changes may be required to
   *	allow a full filesystem lease implementation.

   */

  int vfs_setlease(struct file *filp, long arg, struct file_lock **lease)

  {

  	int error;

  	lock_flocks();
  	error = __vfs_setlease(filp, arg, lease);
  	unlock_flocks();

  
  	return error;
  }

  EXPORT_SYMBOL_GPL(vfs_setlease);

  static int do_fcntl_delete_lease(struct file *filp)
  {
  	struct file_lock fl, *flp = &fl;
  
  	lease_init(filp, F_UNLCK, flp);
  
  	return vfs_setlease(filp, F_UNLCK, &flp);
  }
  
  static int do_fcntl_add_lease(unsigned int fd, struct file *filp, long arg)

  {

  	struct file_lock *fl, *ret;

  	struct fasync_struct *new;

  	int error;

  	fl = lease_alloc(filp, arg);
  	if (IS_ERR(fl))
  		return PTR_ERR(fl);

  	new = fasync_alloc();
  	if (!new) {
  		locks_free_lock(fl);
  		return -ENOMEM;
  	}

  	ret = fl;

  	lock_flocks();

  	error = __vfs_setlease(filp, arg, &ret);

  	if (error) {
  		unlock_flocks();
  		locks_free_lock(fl);
  		goto out_free_fasync;
  	}

  	if (ret != fl)
  		locks_free_lock(fl);

  	/*
  	 * fasync_insert_entry() returns the old entry if any.
  	 * If there was no old entry, then it used 'new' and
  	 * inserted it into the fasync list. Clear new so that
  	 * we don't release it here.
  	 */

  	if (!fasync_insert_entry(fd, filp, &ret->fl_fasync, new))

  		new = NULL;

  	error = __f_setown(filp, task_pid(current), PIDTYPE_PID, 0);

  	unlock_flocks();

  
  out_free_fasync:

  	if (new)
  		fasync_free(new);

  	return error;
  }
  
  /**

   *	fcntl_setlease	-	sets a lease on an open file
   *	@fd: open file descriptor
   *	@filp: file pointer
   *	@arg: type of lease to obtain
   *
   *	Call this fcntl to establish a lease on the file.
   *	Note that you also need to call %F_SETSIG to
   *	receive a signal when the lease is broken.
   */
  int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
  {
  	if (arg == F_UNLCK)
  		return do_fcntl_delete_lease(filp);
  	return do_fcntl_add_lease(fd, filp, arg);
  }
  
  /**

   * flock_lock_file_wait - Apply a FLOCK-style lock to a file
   * @filp: The file to apply the lock to
   * @fl: The lock to be applied
   *
   * Add a FLOCK style lock to a file.
   */
  int flock_lock_file_wait(struct file *filp, struct file_lock *fl)
  {
  	int error;
  	might_sleep();
  	for (;;) {
  		error = flock_lock_file(filp, fl);

  		if (error != FILE_LOCK_DEFERRED)

  			break;
  		error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
  		if (!error)
  			continue;
  
  		locks_delete_block(fl);
  		break;
  	}
  	return error;
  }
  
  EXPORT_SYMBOL(flock_lock_file_wait);
  
  /**
   *	sys_flock: - flock() system call.
   *	@fd: the file descriptor to lock.
   *	@cmd: the type of lock to apply.
   *
   *	Apply a %FL_FLOCK style lock to an open file descriptor.
   *	The @cmd can be one of
   *
   *	%LOCK_SH -- a shared lock.
   *
   *	%LOCK_EX -- an exclusive lock.
   *
   *	%LOCK_UN -- remove an existing lock.
   *
   *	%LOCK_MAND -- a `mandatory' flock.  This exists to emulate Windows Share Modes.
   *
   *	%LOCK_MAND can be combined with %LOCK_READ or %LOCK_WRITE to allow other
   *	processes read and write access respectively.
   */

  SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)

  {
  	struct file *filp;
  	struct file_lock *lock;
  	int can_sleep, unlock;
  	int error;
  
  	error = -EBADF;
  	filp = fget(fd);
  	if (!filp)
  		goto out;
  
  	can_sleep = !(cmd & LOCK_NB);
  	cmd &= ~LOCK_NB;
  	unlock = (cmd == LOCK_UN);

  	if (!unlock && !(cmd & LOCK_MAND) &&
  	    !(filp->f_mode & (FMODE_READ|FMODE_WRITE)))

  		goto out_putf;
  
  	error = flock_make_lock(filp, &lock, cmd);
  	if (error)
  		goto out_putf;
  	if (can_sleep)
  		lock->fl_flags |= FL_SLEEP;

  	error = security_file_lock(filp, lock->fl_type);

  	if (error)
  		goto out_free;
  
  	if (filp->f_op && filp->f_op->flock)
  		error = filp->f_op->flock(filp,
  					  (can_sleep) ? F_SETLKW : F_SETLK,
  					  lock);
  	else
  		error = flock_lock_file_wait(filp, lock);
  
   out_free:

  	locks_free_lock(lock);

  
   out_putf:
  	fput(filp);
   out:
  	return error;
  }

  /**
   * vfs_test_lock - test file byte range lock
   * @filp: The file to test lock for

   * @fl: The lock to test; also used to hold result

   *
   * Returns -ERRNO on failure.  Indicates presence of conflicting lock by
   * setting conf->fl_type to something other than F_UNLCK.
   */
  int vfs_test_lock(struct file *filp, struct file_lock *fl)
  {
  	if (filp->f_op && filp->f_op->lock)
  		return filp->f_op->lock(filp, F_GETLK, fl);
  	posix_test_lock(filp, fl);
  	return 0;
  }
  EXPORT_SYMBOL_GPL(vfs_test_lock);

  static int posix_lock_to_flock(struct flock *flock, struct file_lock *fl)
  {
  	flock->l_pid = fl->fl_pid;
  #if BITS_PER_LONG == 32
  	/*
  	 * Make sure we can represent the posix lock via
  	 * legacy 32bit flock.
  	 */
  	if (fl->fl_start > OFFT_OFFSET_MAX)
  		return -EOVERFLOW;
  	if (fl->fl_end != OFFSET_MAX && fl->fl_end > OFFT_OFFSET_MAX)
  		return -EOVERFLOW;
  #endif
  	flock->l_start = fl->fl_start;
  	flock->l_len = fl->fl_end == OFFSET_MAX ? 0 :
  		fl->fl_end - fl->fl_start + 1;
  	flock->l_whence = 0;

  	flock->l_type = fl->fl_type;

  	return 0;
  }
  
  #if BITS_PER_LONG == 32
  static void posix_lock_to_flock64(struct flock64 *flock, struct file_lock *fl)
  {
  	flock->l_pid = fl->fl_pid;
  	flock->l_start = fl->fl_start;
  	flock->l_len = fl->fl_end == OFFSET_MAX ? 0 :
  		fl->fl_end - fl->fl_start + 1;
  	flock->l_whence = 0;
  	flock->l_type = fl->fl_type;
  }
  #endif

  /* Report the first existing lock that would conflict with l.
   * This implements the F_GETLK command of fcntl().
   */
  int fcntl_getlk(struct file *filp, struct flock __user *l)
  {

  	struct file_lock file_lock;

  	struct flock flock;
  	int error;
  
  	error = -EFAULT;
  	if (copy_from_user(&flock, l, sizeof(flock)))
  		goto out;
  	error = -EINVAL;
  	if ((flock.l_type != F_RDLCK) && (flock.l_type != F_WRLCK))
  		goto out;
  
  	error = flock_to_posix_lock(filp, &file_lock, &flock);
  	if (error)
  		goto out;

  	error = vfs_test_lock(filp, &file_lock);
  	if (error)
  		goto out;

  	flock.l_type = file_lock.fl_type;
  	if (file_lock.fl_type != F_UNLCK) {
  		error = posix_lock_to_flock(&flock, &file_lock);

  		if (error)

  			goto out;

  	}
  	error = -EFAULT;
  	if (!copy_to_user(l, &flock, sizeof(flock)))
  		error = 0;
  out:
  	return error;
  }

  /**
   * vfs_lock_file - file byte range lock
   * @filp: The file to apply the lock to
   * @cmd: type of locking operation (F_SETLK, F_GETLK, etc.)
   * @fl: The lock to be applied

   * @conf: Place to return a copy of the conflicting lock, if found.
   *
   * A caller that doesn't care about the conflicting lock may pass NULL
   * as the final argument.
   *
   * If the filesystem defines a private ->lock() method, then @conf will
   * be left unchanged; so a caller that cares should initialize it to
   * some acceptable default.

   *
   * To avoid blocking kernel daemons, such as lockd, that need to acquire POSIX
   * locks, the ->lock() interface may return asynchronously, before the lock has
   * been granted or denied by the underlying filesystem, if (and only if)

   * lm_grant is set. Callers expecting ->lock() to return asynchronously

   * will only use F_SETLK, not F_SETLKW; they will set FL_SLEEP if (and only if)
   * the request is for a blocking lock. When ->lock() does return asynchronously,

   * it must return FILE_LOCK_DEFERRED, and call ->lm_grant() when the lock

   * request completes.
   * If the request is for non-blocking lock the file system should return

   * FILE_LOCK_DEFERRED then try to get the lock and call the callback routine
   * with the result. If the request timed out the callback routine will return a

   * nonzero return code and the file system should release the lock. The file
   * system is also responsible to keep a corresponding posix lock when it
   * grants a lock so the VFS can find out which locks are locally held and do
   * the correct lock cleanup when required.
   * The underlying filesystem must not drop the kernel lock or call

   * ->lm_grant() before returning to the caller with a FILE_LOCK_DEFERRED

   * return code.

   */

  int vfs_lock_file(struct file *filp, unsigned int cmd, struct file_lock *fl, struct file_lock *conf)

  {
  	if (filp->f_op && filp->f_op->lock)
  		return filp->f_op->lock(filp, cmd, fl);
  	else

  		return posix_lock_file(filp, fl, conf);

  }
  EXPORT_SYMBOL_GPL(vfs_lock_file);

  static int do_lock_file_wait(struct file *filp, unsigned int cmd,
  			     struct file_lock *fl)
  {
  	int error;
  
  	error = security_file_lock(filp, fl->fl_type);
  	if (error)
  		return error;

  	for (;;) {
  		error = vfs_lock_file(filp, cmd, fl, NULL);
  		if (error != FILE_LOCK_DEFERRED)

  			break;

  		error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
  		if (!error)
  			continue;
  
  		locks_delete_block(fl);
  		break;

  	}
  
  	return error;
  }

  /* Apply the lock described by l to an open file descriptor.
   * This implements both the F_SETLK and F_SETLKW commands of fcntl().
   */

  int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd,
  		struct flock __user *l)

  {
  	struct file_lock *file_lock = locks_alloc_lock();
  	struct flock flock;
  	struct inode *inode;

  	struct file *f;

  	int error;
  
  	if (file_lock == NULL)
  		return -ENOLCK;
  
  	/*
  	 * This might block, so we do it before checking the inode.
  	 */
  	error = -EFAULT;
  	if (copy_from_user(&flock, l, sizeof(flock)))
  		goto out;

  	inode = filp->f_path.dentry->d_inode;

  
  	/* Don't allow mandatory locks on files that may be memory mapped
  	 * and shared.
  	 */

  	if (mandatory_lock(inode) && mapping_writably_mapped(filp->f_mapping)) {

  		error = -EAGAIN;
  		goto out;
  	}

  again:

  	error = flock_to_posix_lock(filp, file_lock, &flock);
  	if (error)
  		goto out;
  	if (cmd == F_SETLKW) {
  		file_lock->fl_flags |= FL_SLEEP;
  	}
  	
  	error = -EBADF;
  	switch (flock.l_type) {
  	case F_RDLCK:
  		if (!(filp->f_mode & FMODE_READ))
  			goto out;
  		break;
  	case F_WRLCK:
  		if (!(filp->f_mode & FMODE_WRITE))
  			goto out;
  		break;
  	case F_UNLCK:
  		break;
  	default:
  		error = -EINVAL;
  		goto out;
  	}

  	error = do_lock_file_wait(filp, cmd, file_lock);

  	/*
  	 * Attempt to detect a close/fcntl race and recover by
  	 * releasing the lock that was just acquired.
  	 */

  	/*
  	 * we need that spin_lock here - it prevents reordering between
  	 * update of inode->i_flock and check for it done in close().
  	 * rcu_read_lock() wouldn't do.
  	 */
  	spin_lock(&current->files->file_lock);
  	f = fcheck(fd);
  	spin_unlock(&current->files->file_lock);
  	if (!error && f != filp && flock.l_type != F_UNLCK) {

  		flock.l_type = F_UNLCK;
  		goto again;

  	}

  out:

  	locks_free_lock(file_lock);
  	return error;
  }
  
  #if BITS_PER_LONG == 32
  /* Report the first existing lock that would conflict with l.
   * This implements the F_GETLK command of fcntl().
   */
  int fcntl_getlk64(struct file *filp, struct flock64 __user *l)
  {

  	struct file_lock file_lock;

  	struct flock64 flock;
  	int error;
  
  	error = -EFAULT;
  	if (copy_from_user(&flock, l, sizeof(flock)))
  		goto out;
  	error = -EINVAL;
  	if ((flock.l_type != F_RDLCK) && (flock.l_type != F_WRLCK))
  		goto out;
  
  	error = flock64_to_posix_lock(filp, &file_lock, &flock);
  	if (error)
  		goto out;

  	error = vfs_test_lock(filp, &file_lock);
  	if (error)
  		goto out;

  	flock.l_type = file_lock.fl_type;
  	if (file_lock.fl_type != F_UNLCK)
  		posix_lock_to_flock64(&flock, &file_lock);

  	error = -EFAULT;
  	if (!copy_to_user(l, &flock, sizeof(flock)))
  		error = 0;
    
  out:
  	return error;
  }
  
  /* Apply the lock described by l to an open file descriptor.
   * This implements both the F_SETLK and F_SETLKW commands of fcntl().
   */

  int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
  		struct flock64 __user *l)

  {
  	struct file_lock *file_lock = locks_alloc_lock();
  	struct flock64 flock;
  	struct inode *inode;

  	struct file *f;

  	int error;
  
  	if (file_lock == NULL)
  		return -ENOLCK;
  
  	/*
  	 * This might block, so we do it before checking the inode.
  	 */
  	error = -EFAULT;
  	if (copy_from_user(&flock, l, sizeof(flock)))
  		goto out;

  	inode = filp->f_path.dentry->d_inode;

  
  	/* Don't allow mandatory locks on files that may be memory mapped
  	 * and shared.
  	 */

  	if (mandatory_lock(inode) && mapping_writably_mapped(filp->f_mapping)) {

  		error = -EAGAIN;
  		goto out;
  	}

  again:

  	error = flock64_to_posix_lock(filp, file_lock, &flock);
  	if (error)
  		goto out;
  	if (cmd == F_SETLKW64) {
  		file_lock->fl_flags |= FL_SLEEP;
  	}
  	
  	error = -EBADF;
  	switch (flock.l_type) {
  	case F_RDLCK:
  		if (!(filp->f_mode & FMODE_READ))
  			goto out;
  		break;
  	case F_WRLCK:
  		if (!(filp->f_mode & FMODE_WRITE))
  			goto out;
  		break;
  	case F_UNLCK:
  		break;
  	default:
  		error = -EINVAL;
  		goto out;
  	}

  	error = do_lock_file_wait(filp, cmd, file_lock);

  	/*
  	 * Attempt to detect a close/fcntl race and recover by
  	 * releasing the lock that was just acquired.
  	 */

  	spin_lock(&current->files->file_lock);
  	f = fcheck(fd);
  	spin_unlock(&current->files->file_lock);
  	if (!error && f != filp && flock.l_type != F_UNLCK) {

  		flock.l_type = F_UNLCK;
  		goto again;

  	}
  
  out:
  	locks_free_lock(file_lock);
  	return error;
  }
  #endif /* BITS_PER_LONG == 32 */
  
  /*
   * This function is called when the file is being removed
   * from the task's fd array.  POSIX locks belonging to this task
   * are deleted at this time.
   */
  void locks_remove_posix(struct file *filp, fl_owner_t owner)
  {

  	struct file_lock lock;

  
  	/*
  	 * If there are no locks held on this file, we don't need to call
  	 * posix_lock_file().  Another process could be setting a lock on this
  	 * file at the same time, but we wouldn't remove that lock anyway.
  	 */

  	if (!filp->f_path.dentry->d_inode->i_flock)

  		return;
  
  	lock.fl_type = F_UNLCK;

  	lock.fl_flags = FL_POSIX | FL_CLOSE;

  	lock.fl_start = 0;
  	lock.fl_end = OFFSET_MAX;
  	lock.fl_owner = owner;
  	lock.fl_pid = current->tgid;
  	lock.fl_file = filp;
  	lock.fl_ops = NULL;
  	lock.fl_lmops = NULL;

  	vfs_lock_file(filp, F_SETLK, &lock, NULL);

  	if (lock.fl_ops && lock.fl_ops->fl_release_private)
  		lock.fl_ops->fl_release_private(&lock);
  }
  
  EXPORT_SYMBOL(locks_remove_posix);
  
  /*
   * This function is called on the last close of an open file.
   */
  void locks_remove_flock(struct file *filp)
  {

  	struct inode * inode = filp->f_path.dentry->d_inode;

  	struct file_lock *fl;
  	struct file_lock **before;
  
  	if (!inode->i_flock)
  		return;
  
  	if (filp->f_op && filp->f_op->flock) {
  		struct file_lock fl = {
  			.fl_pid = current->tgid,
  			.fl_file = filp,
  			.fl_flags = FL_FLOCK,
  			.fl_type = F_UNLCK,
  			.fl_end = OFFSET_MAX,
  		};
  		filp->f_op->flock(filp, F_SETLKW, &fl);

  		if (fl.fl_ops && fl.fl_ops->fl_release_private)
  			fl.fl_ops->fl_release_private(&fl);

  	}

  	lock_flocks();

  	before = &inode->i_flock;
  
  	while ((fl = *before) != NULL) {
  		if (fl->fl_file == filp) {

  			if (IS_FLOCK(fl)) {

  				locks_delete_lock(before);
  				continue;
  			}
  			if (IS_LEASE(fl)) {
  				lease_modify(before, F_UNLCK);
  				continue;
  			}
  			/* What? */
  			BUG();
   		}
  		before = &fl->fl_next;
  	}

  	unlock_flocks();

  }
  
  /**

   *	posix_unblock_lock - stop waiting for a file lock
   *      @filp:   how the file was opened
   *	@waiter: the lock which was waiting
   *
   *	lockd needs to block waiting for locks.
   */

  int

  posix_unblock_lock(struct file *filp, struct file_lock *waiter)
  {

  	int status = 0;

  	lock_flocks();

  	if (waiter->fl_next)

  		__locks_delete_block(waiter);

  	else
  		status = -ENOENT;

  	unlock_flocks();

  	return status;

  }
  
  EXPORT_SYMBOL(posix_unblock_lock);

  /**
   * vfs_cancel_lock - file byte range unblock lock
   * @filp: The file to apply the unblock to
   * @fl: The lock to be unblocked
   *
   * Used by lock managers to cancel blocked requests
   */
  int vfs_cancel_lock(struct file *filp, struct file_lock *fl)
  {
  	if (filp->f_op && filp->f_op->lock)
  		return filp->f_op->lock(filp, F_CANCELLK, fl);
  	return 0;
  }
  
  EXPORT_SYMBOL_GPL(vfs_cancel_lock);

  #ifdef CONFIG_PROC_FS

  #include <linux/proc_fs.h>

  #include <linux/seq_file.h>
  
  static void lock_get_status(struct seq_file *f, struct file_lock *fl,

  			    loff_t id, char *pfx)

  {
  	struct inode *inode = NULL;

  	unsigned int fl_pid;
  
  	if (fl->fl_nspid)

  		fl_pid = pid_vnr(fl->fl_nspid);

  	else
  		fl_pid = fl->fl_pid;

  
  	if (fl->fl_file != NULL)

  		inode = fl->fl_file->f_path.dentry->d_inode;

  	seq_printf(f, "%lld:%s ", id, pfx);

  	if (IS_POSIX(fl)) {

  		seq_printf(f, "%6s %s ",

  			     (fl->fl_flags & FL_ACCESS) ? "ACCESS" : "POSIX ",
  			     (inode == NULL) ? "*NOINODE*" :

  			     mandatory_lock(inode) ? "MANDATORY" : "ADVISORY ");

  	} else if (IS_FLOCK(fl)) {
  		if (fl->fl_type & LOCK_MAND) {

  			seq_printf(f, "FLOCK  MSNFS     ");

  		} else {

  			seq_printf(f, "FLOCK  ADVISORY  ");

  		}
  	} else if (IS_LEASE(fl)) {

  		seq_printf(f, "LEASE  ");

  		if (fl->fl_type & F_INPROGRESS)

  			seq_printf(f, "BREAKING  ");

  		else if (fl->fl_file)

  			seq_printf(f, "ACTIVE    ");

  		else

  			seq_printf(f, "BREAKER   ");

  	} else {

  		seq_printf(f, "UNKNOWN UNKNOWN  ");

  	}
  	if (fl->fl_type & LOCK_MAND) {

  		seq_printf(f, "%s ",

  			       (fl->fl_type & LOCK_READ)
  			       ? (fl->fl_type & LOCK_WRITE) ? "RW   " : "READ "
  			       : (fl->fl_type & LOCK_WRITE) ? "WRITE" : "NONE ");
  	} else {

  		seq_printf(f, "%s ",

  			       (fl->fl_type & F_INPROGRESS)
  			       ? (fl->fl_type & F_UNLCK) ? "UNLCK" : "READ "
  			       : (fl->fl_type & F_WRLCK) ? "WRITE" : "READ ");
  	}
  	if (inode) {
  #ifdef WE_CAN_BREAK_LSLK_NOW

  		seq_printf(f, "%d %s:%ld ", fl_pid,

  				inode->i_sb->s_id, inode->i_ino);
  #else
  		/* userspace relies on this representation of dev_t ;-( */

  		seq_printf(f, "%d %02x:%02x:%ld ", fl_pid,

  				MAJOR(inode->i_sb->s_dev),
  				MINOR(inode->i_sb->s_dev), inode->i_ino);
  #endif
  	} else {

  		seq_printf(f, "%d <none>:0 ", fl_pid);

  	}
  	if (IS_POSIX(fl)) {
  		if (fl->fl_end == OFFSET_MAX)

  			seq_printf(f, "%Ld EOF
  ", fl->fl_start);

  		else

  			seq_printf(f, "%Ld %Ld
  ", fl->fl_start, fl->fl_end);

  	} else {

  		seq_printf(f, "0 EOF
  ");

  	}
  }

  static int locks_show(struct seq_file *f, void *v)

  {

  	struct file_lock *fl, *bfl;

  	fl = list_entry(v, struct file_lock, fl_link);

  	lock_get_status(f, fl, *((loff_t *)f->private), "");

  	list_for_each_entry(bfl, &fl->fl_block, fl_block)

  		lock_get_status(f, bfl, *((loff_t *)f->private), " ->");

  	return 0;
  }

  static void *locks_start(struct seq_file *f, loff_t *pos)
  {

  	loff_t *p = f->private;

  	lock_flocks();

  	*p = (*pos + 1);

  	return seq_list_start(&file_lock_list, *pos);
  }

  static void *locks_next(struct seq_file *f, void *v, loff_t *pos)
  {

  	loff_t *p = f->private;
  	++*p;

  	return seq_list_next(v, &file_lock_list, pos);
  }

  static void locks_stop(struct seq_file *f, void *v)
  {

  	unlock_flocks();

  }

  static const struct seq_operations locks_seq_operations = {

  	.start	= locks_start,
  	.next	= locks_next,
  	.stop	= locks_stop,
  	.show	= locks_show,
  };

  
  static int locks_open(struct inode *inode, struct file *filp)
  {

  	return seq_open_private(filp, &locks_seq_operations, sizeof(loff_t));

  }
  
  static const struct file_operations proc_locks_operations = {
  	.open		= locks_open,
  	.read		= seq_read,
  	.llseek		= seq_lseek,

  	.release	= seq_release_private,

  };
  
  static int __init proc_locks_init(void)
  {
  	proc_create("locks", 0, NULL, &proc_locks_operations);
  	return 0;
  }
  module_init(proc_locks_init);

  #endif

  /**
   *	lock_may_read - checks that the region is free of locks
   *	@inode: the inode that is being read
   *	@start: the first byte to read
   *	@len: the number of bytes to read
   *
   *	Emulates Windows locking requirements.  Whole-file
   *	mandatory locks (share modes) can prohibit a read and
   *	byte-range POSIX locks can prohibit a read if they overlap.
   *
   *	N.B. this function is only ever called
   *	from knfsd and ownership of locks is never checked.
   */
  int lock_may_read(struct inode *inode, loff_t start, unsigned long len)
  {
  	struct file_lock *fl;
  	int result = 1;

  	lock_flocks();

  	for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
  		if (IS_POSIX(fl)) {
  			if (fl->fl_type == F_RDLCK)
  				continue;
  			if ((fl->fl_end < start) || (fl->fl_start > (start + len)))
  				continue;
  		} else if (IS_FLOCK(fl)) {
  			if (!(fl->fl_type & LOCK_MAND))
  				continue;
  			if (fl->fl_type & LOCK_READ)
  				continue;
  		} else
  			continue;
  		result = 0;
  		break;
  	}

  	unlock_flocks();

  	return result;
  }
  
  EXPORT_SYMBOL(lock_may_read);
  
  /**
   *	lock_may_write - checks that the region is free of locks
   *	@inode: the inode that is being written
   *	@start: the first byte to write
   *	@len: the number of bytes to write
   *
   *	Emulates Windows locking requirements.  Whole-file
   *	mandatory locks (share modes) can prohibit a write and
   *	byte-range POSIX locks can prohibit a write if they overlap.
   *
   *	N.B. this function is only ever called
   *	from knfsd and ownership of locks is never checked.
   */
  int lock_may_write(struct inode *inode, loff_t start, unsigned long len)
  {
  	struct file_lock *fl;
  	int result = 1;

  	lock_flocks();

  	for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
  		if (IS_POSIX(fl)) {
  			if ((fl->fl_end < start) || (fl->fl_start > (start + len)))
  				continue;
  		} else if (IS_FLOCK(fl)) {
  			if (!(fl->fl_type & LOCK_MAND))
  				continue;
  			if (fl->fl_type & LOCK_WRITE)
  				continue;
  		} else
  			continue;
  		result = 0;
  		break;
  	}

  	unlock_flocks();

  	return result;
  }
  
  EXPORT_SYMBOL(lock_may_write);

  static int __init filelock_init(void)
  {
  	filelock_cache = kmem_cache_create("file_lock_cache",

  			sizeof(struct file_lock), 0, SLAB_PANIC, NULL);

  	return 0;
  }
  
  core_initcall(filelock_init);