/*
   *  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/fs.h>
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/security.h>
  #include <linux/slab.h>
  #include <linux/smp_lock.h>
  #include <linux/syscalls.h>
  #include <linux/time.h>

  #include <linux/rcupdate.h>

  
  #include <asm/semaphore.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 kmem_cache_t *filelock_cache __read_mostly;

  
  /* Allocate an empty lock structure. */
  static struct file_lock *locks_alloc_lock(void)
  {
  	return kmem_cache_alloc(filelock_cache, SLAB_KERNEL);
  }

  static 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->fl_release_private)
  			fl->fl_lmops->fl_release_private(fl);
  		fl->fl_lmops = NULL;
  	}
  
  }

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

  static 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);
  }
  
  void locks_init_lock(struct file_lock *fl)
  {
  	INIT_LIST_HEAD(&fl->fl_link);
  	INIT_LIST_HEAD(&fl->fl_block);
  	init_waitqueue_head(&fl->fl_wait);
  	fl->fl_next = NULL;
  	fl->fl_fasync = NULL;
  	fl->fl_owner = NULL;
  	fl->fl_pid = 0;
  	fl->fl_file = NULL;
  	fl->fl_flags = 0;
  	fl->fl_type = 0;
  	fl->fl_start = fl->fl_end = 0;
  	fl->fl_ops = NULL;
  	fl->fl_lmops = NULL;
  }
  
  EXPORT_SYMBOL(locks_init_lock);
  
  /*
   * Initialises the fields of the file lock which are invariant for
   * free file_locks.
   */
  static void init_once(void *foo, kmem_cache_t *cache, unsigned long flags)
  {
  	struct file_lock *lock = (struct file_lock *) foo;
  
  	if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) !=
  					SLAB_CTOR_CONSTRUCTOR)
  		return;
  
  	locks_init_lock(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) {
  		if (fl->fl_lmops->fl_copy_lock)
  			fl->fl_lmops->fl_copy_lock(new, fl);
  		new->fl_lmops = fl->fl_lmops;
  	}
  }

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

  static 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;
  }
  
  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 0: /*SEEK_SET*/
  		start = 0;
  		break;
  	case 1: /*SEEK_CUR*/
  		start = filp->f_pos;
  		break;
  	case 2: /*SEEK_END*/
  		start = i_size_read(filp->f_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 0: /*SEEK_SET*/
  		start = 0;
  		break;
  	case 1: /*SEEK_CUR*/
  		start = filp->f_pos;
  		break;
  	case 2: /*SEEK_END*/
  		start = i_size_read(filp->f_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;
  
  	switch (l->l_type) {
  	case F_RDLCK:
  	case F_WRLCK:
  	case F_UNLCK:
  		fl->fl_type = l->l_type;
  		break;
  	default:
  		return -EINVAL;
  	}
  
  	return (0);
  }
  #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 int lease_mylease_callback(struct file_lock *fl, struct file_lock *try)

  {
  	return fl->fl_file == try->fl_file;
  }

  static struct lock_manager_operations lease_manager_ops = {

  	.fl_break = lease_break_callback,
  	.fl_release_private = lease_release_private_callback,
  	.fl_mylease = lease_mylease_callback,
  	.fl_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 int lease_alloc(struct file *filp, int type, struct file_lock **flp)
  {
  	struct file_lock *fl = locks_alloc_lock();

  	int error = -ENOMEM;

  
  	if (fl == NULL)

  		goto out;

  
  	error = lease_init(filp, type, fl);

  	if (error) {
  		locks_free_lock(fl);
  		fl = NULL;
  	}
  out:

  	*flp = fl;

  	return error;

  }
  
  /* 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->fl_compare_owner)
  		return fl2->fl_lmops == fl1->fl_lmops &&
  			fl1->fl_lmops->fl_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_kernel();
  	__locks_delete_block(waiter);
  	unlock_kernel();
  }
  
  /* 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 = list_entry(blocker->fl_block.next,
  				struct file_lock, fl_block);
  		__locks_delete_block(waiter);
  		if (waiter->fl_lmops && waiter->fl_lmops->fl_notify)
  			waiter->fl_lmops->fl_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);
  
  	/* insert into file's list */
  	fl->fl_next = *pos;
  	*pos = fl;
  
  	if (fl->fl_ops && fl->fl_ops->fl_insert)
  		fl->fl_ops->fl_insert(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_ops && fl->fl_ops->fl_remove)
  		fl->fl_ops->fl_remove(fl);
  
  	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));
  }
  
  static int interruptible_sleep_on_locked(wait_queue_head_t *fl_wait, int timeout)
  {
  	int result = 0;
  	DECLARE_WAITQUEUE(wait, current);
  
  	__set_current_state(TASK_INTERRUPTIBLE);
  	add_wait_queue(fl_wait, &wait);
  	if (timeout == 0)
  		schedule();
  	else
  		result = schedule_timeout(timeout);
  	if (signal_pending(current))
  		result = -ERESTARTSYS;
  	remove_wait_queue(fl_wait, &wait);
  	__set_current_state(TASK_RUNNING);
  	return result;
  }
  
  static int locks_block_on_timeout(struct file_lock *blocker, struct file_lock *waiter, int time)
  {
  	int result;
  	locks_insert_block(blocker, waiter);
  	result = interruptible_sleep_on_locked(&waiter->fl_wait, time);
  	__locks_delete_block(waiter);
  	return result;
  }

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

  {
  	struct file_lock *cfl;
  
  	lock_kernel();
  	for (cfl = filp->f_dentry->d_inode->i_flock; cfl; cfl = cfl->fl_next) {
  		if (!IS_POSIX(cfl))
  			continue;
  		if (posix_locks_conflict(cfl, fl))
  			break;
  	}

  	if (cfl) {

  		__locks_copy_lock(conflock, cfl);

  		unlock_kernel();
  		return 1;
  	}

  	unlock_kernel();

  	return 0;

  }
  
  EXPORT_SYMBOL(posix_test_lock);
  
  /* This function tests for deadlock condition before putting a process to
   * sleep. The detection scheme is no longer recursive. Recursive was neat,
   * but dangerous - we risked stack corruption if the lock data was bad, or
   * if the recursion was too deep for any other reason.
   *
   * We rely on the fact that a task can only be on one lock's wait queue
   * at a time. When we find blocked_task on a wait queue we can re-search
   * with blocked_task equal to that queue's owner, until either blocked_task
   * isn't found, or blocked_task is found on a queue owned by my_task.
   *
   * Note: the above assumption may not be true when handling lock requests
   * from a broken NFS client. But broken NFS clients have a lot more to
   * worry about than proper deadlock detection anyway... --okir
   */

  static int posix_locks_deadlock(struct file_lock *caller_fl,

  				struct file_lock *block_fl)
  {
  	struct list_head *tmp;
  
  next_task:
  	if (posix_same_owner(caller_fl, block_fl))
  		return 1;
  	list_for_each(tmp, &blocked_list) {
  		struct file_lock *fl = list_entry(tmp, struct file_lock, fl_link);
  		if (posix_same_owner(fl, block_fl)) {
  			fl = fl->fl_next;
  			block_fl = fl;
  			goto next_task;
  		}
  	}
  	return 0;
  }

  /* Try to create a FLOCK lock on filp. We always insert new FLOCK locks
   * at the head of the list, but that's secret knowledge known only to
   * flock_lock_file and posix_lock_file.
   */

  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_dentry->d_inode;
  	int error = 0;
  	int found = 0;
  
  	lock_kernel();
  	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)
  		goto out;

  	error = -ENOMEM;

  	new_fl = locks_alloc_lock();
  	if (new_fl == NULL)
  		goto out;

  	/*
  	 * If a higher-priority process was blocked on the old file lock,
  	 * give it the opportunity to lock the file.
  	 */
  	if (found)
  		cond_resched();

  	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)
  			locks_insert_block(fl, request);

  		goto out;
  	}

  	locks_copy_lock(new_fl, request);

  	locks_insert_lock(&inode->i_flock, new_fl);

  	new_fl = NULL;

  	error = 0;

  
  out:
  	unlock_kernel();

  	if (new_fl)
  		locks_free_lock(new_fl);

  	return error;
  }

  static int __posix_lock_file_conf(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_kernel();
  	if (request->fl_type != F_UNLCK) {
  		for_each_lock(inode, before) {
  			struct file_lock *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 = -EAGAIN;
  			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)
  			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_kernel();
  	/*
  	 * 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
   *
   * 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(struct file *filp, struct file_lock *fl)
  {

  	return __posix_lock_file_conf(filp->f_dentry->d_inode, fl, NULL);
  }
  EXPORT_SYMBOL(posix_lock_file);
  
  /**
   * posix_lock_file_conf - 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.
   *
   * Except for the conflock parameter, acts just like posix_lock_file.
   */
  int posix_lock_file_conf(struct file *filp, struct file_lock *fl,
  			struct file_lock *conflock)
  {
  	return __posix_lock_file_conf(filp->f_dentry->d_inode, fl, conflock);

  }

  EXPORT_SYMBOL(posix_lock_file_conf);

  
  /**
   * 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);

  		if ((error != -EAGAIN) || !(fl->fl_flags & FL_SLEEP))
  			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_kernel();
  	for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
  		if (!IS_POSIX(fl))
  			continue;
  		if (fl->fl_owner != owner)
  			break;
  	}
  	unlock_kernel();
  	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_conf(inode, &fl, NULL);

  		if (error != -EAGAIN)
  			break;
  		if (!(fl.fl_flags & FL_SLEEP))
  			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 ((inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
  				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 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;
  	int alloc_err;
  	unsigned long break_time;
  	int i_have_this_lease = 0;
  
  	alloc_err = lease_alloc(NULL, mode & FMODE_WRITE ? F_WRLCK : F_RDLCK,
  			&new_fl);
  
  	lock_kernel();
  
  	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 (mode & FMODE_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 (alloc_err && !i_have_this_lease && ((mode & O_NONBLOCK) == 0)) {
  		error = alloc_err;
  		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->fl_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++;
  	}
  	error = locks_block_on_timeout(flock, new_fl, break_time);
  	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_kernel();
  	if (!alloc_err)
  		locks_free_lock(new_fl);
  	return error;
  }
  
  EXPORT_SYMBOL(__break_lease);
  
  /**
   *	lease_get_mtime
   *	@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 modifiying 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_kernel();
  	time_out_leases(filp->f_dentry->d_inode);
  	for (fl = filp->f_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_kernel();
  	return type;
  }
  
  /**
   *	__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->fl_break function is required
   *	by break_lease().
   *
   *	Called with kernel lock held.
   */

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

  {

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

  	struct dentry *dentry = filp->f_dentry;
  	struct inode *inode = dentry->d_inode;
  	int error, rdlease_count = 0, wrlease_count = 0;
  
  	time_out_leases(inode);
  
  	error = -EINVAL;
  	if (!flp || !(*flp) || !(*flp)->fl_lmops || !(*flp)->fl_lmops->fl_break)
  		goto out;

  	lease = *flp;

  	error = -EAGAIN;
  	if ((arg == F_RDLCK) && (atomic_read(&inode->i_writecount) > 0))
  		goto out;
  	if ((arg == F_WRLCK)
  	    && ((atomic_read(&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 (lease->fl_lmops->fl_mylease(fl, lease))
  			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++;
  	}
  
  	if ((arg == F_RDLCK && (wrlease_count > 0)) ||
  	    (arg == F_WRLCK && ((rdlease_count + wrlease_count) > 0)))
  		goto out;
  
  	if (my_before != NULL) {

  		*flp = *my_before;

  		error = lease->fl_lmops->fl_change(my_before, arg);
  		goto out;
  	}
  
  	error = 0;
  	if (arg == F_UNLCK)
  		goto out;
  
  	error = -EINVAL;
  	if (!leases_enable)
  		goto out;
  
  	error = lease_alloc(filp, arg, &fl);
  	if (error)
  		goto out;
  
  	locks_copy_lock(fl, lease);
  
  	locks_insert_lock(before, fl);
  
  	*flp = fl;
  out:
  	return error;
  }
  
   /**
   *	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 fl_lmops fl_break function is required by break_lease
   */
  
  int setlease(struct file *filp, long arg, struct file_lock **lease)
  {
  	struct dentry *dentry = filp->f_dentry;
  	struct inode *inode = dentry->d_inode;
  	int error;
  
  	if ((current->fsuid != inode->i_uid) && !capable(CAP_LEASE))
  		return -EACCES;
  	if (!S_ISREG(inode->i_mode))
  		return -EINVAL;
  	error = security_file_lock(filp, arg);
  	if (error)
  		return error;
  
  	lock_kernel();
  	error = __setlease(filp, arg, lease);
  	unlock_kernel();
  
  	return error;
  }
  
  EXPORT_SYMBOL(setlease);
  
  /**
   *	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)
  {
  	struct file_lock fl, *flp = &fl;
  	struct dentry *dentry = filp->f_dentry;
  	struct inode *inode = dentry->d_inode;
  	int error;
  
  	if ((current->fsuid != inode->i_uid) && !capable(CAP_LEASE))
  		return -EACCES;
  	if (!S_ISREG(inode->i_mode))
  		return -EINVAL;
  	error = security_file_lock(filp, arg);
  	if (error)
  		return error;
  
  	locks_init_lock(&fl);
  	error = lease_init(filp, arg, &fl);
  	if (error)
  		return error;
  
  	lock_kernel();
  
  	error = __setlease(filp, arg, &flp);

  	if (error || arg == F_UNLCK)

  		goto out_unlock;
  
  	error = fasync_helper(fd, filp, 1, &flp->fl_fasync);
  	if (error < 0) {
  		/* remove lease just inserted by __setlease */
  		flp->fl_type = F_UNLCK | F_INPROGRESS;
  		flp->fl_break_time = jiffies- 10;
  		time_out_leases(inode);
  		goto out_unlock;
  	}
  
  	error = f_setown(filp, current->pid, 0);
  out_unlock:
  	unlock_kernel();
  	return error;
  }
  
  /**
   * 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 != -EAGAIN) || !(fl->fl_flags & FL_SLEEP))
  			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.
   */
  asmlinkage long sys_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 & 3))
  		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, cmd);
  	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;
  }
  
  /* 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 *fl, cfl, 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;
  
  	if (filp->f_op && filp->f_op->lock) {
  		error = filp->f_op->lock(filp, F_GETLK, &file_lock);

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

  		if (error < 0)
  			goto out;
  		else
  		  fl = (file_lock.fl_type == F_UNLCK ? NULL : &file_lock);
  	} else {

  		fl = (posix_test_lock(filp, &file_lock, &cfl) ? &cfl : NULL);

  	}
   
  	flock.l_type = F_UNLCK;
  	if (fl != NULL) {
  		flock.l_pid = fl->fl_pid;
  #if BITS_PER_LONG == 32
  		/*
  		 * Make sure we can represent the posix lock via
  		 * legacy 32bit flock.
  		 */
  		error = -EOVERFLOW;
  		if (fl->fl_start > OFFT_OFFSET_MAX)
  			goto out;
  		if ((fl->fl_end != OFFSET_MAX)
  		    && (fl->fl_end > OFFT_OFFSET_MAX))
  			goto out;
  #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;
  	}
  	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_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;
  	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_dentry->d_inode;
  
  	/* Don't allow mandatory locks on files that may be memory mapped
  	 * and shared.
  	 */
  	if (IS_MANDLOCK(inode) &&
  	    (inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID &&
  	    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 = security_file_lock(filp, file_lock->fl_type);
  	if (error)
  		goto out;

  	if (filp->f_op && filp->f_op->lock != NULL)

  		error = filp->f_op->lock(filp, cmd, file_lock);

  	else {
  		for (;;) {

  			error = posix_lock_file(filp, file_lock);

  			if ((error != -EAGAIN) || (cmd == F_SETLK))
  				break;
  			error = wait_event_interruptible(file_lock->fl_wait,
  					!file_lock->fl_next);
  			if (!error)
  				continue;

  			locks_delete_block(file_lock);

  			break;

  		}
  	}

  	/*
  	 * Attempt to detect a close/fcntl race and recover by
  	 * releasing the lock that was just acquired.
  	 */
  	if (!error && fcheck(fd) != 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 *fl, cfl, 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;
  
  	if (filp->f_op && filp->f_op->lock) {
  		error = filp->f_op->lock(filp, F_GETLK, &file_lock);

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

  		if (error < 0)
  			goto out;
  		else
  		  fl = (file_lock.fl_type == F_UNLCK ? NULL : &file_lock);
  	} else {

  		fl = (posix_test_lock(filp, &file_lock, &cfl) ? &cfl : NULL);

  	}
   
  	flock.l_type = F_UNLCK;
  	if (fl != NULL) {
  		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;
  	}
  	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;
  	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_dentry->d_inode;
  
  	/* Don't allow mandatory locks on files that may be memory mapped
  	 * and shared.
  	 */
  	if (IS_MANDLOCK(inode) &&
  	    (inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID &&
  	    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 = security_file_lock(filp, file_lock->fl_type);
  	if (error)
  		goto out;

  	if (filp->f_op && filp->f_op->lock != NULL)

  		error = filp->f_op->lock(filp, cmd, file_lock);

  	else {
  		for (;;) {

  			error = posix_lock_file(filp, file_lock);

  			if ((error != -EAGAIN) || (cmd == F_SETLK64))
  				break;
  			error = wait_event_interruptible(file_lock->fl_wait,
  					!file_lock->fl_next);
  			if (!error)
  				continue;

  			locks_delete_block(file_lock);

  			break;

  		}
  	}

  	/*
  	 * Attempt to detect a close/fcntl race and recover by
  	 * releasing the lock that was just acquired.
  	 */
  	if (!error && fcheck(fd) != 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_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;

  	if (filp->f_op && filp->f_op->lock != NULL)

  		filp->f_op->lock(filp, F_SETLK, &lock);

  	else
  		posix_lock_file(filp, &lock);

  	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_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_kernel();
  	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_kernel();
  }
  
  /**

   *	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_kernel();

  	if (waiter->fl_next)

  		__locks_delete_block(waiter);

  	else
  		status = -ENOENT;

  	unlock_kernel();

  	return status;

  }
  
  EXPORT_SYMBOL(posix_unblock_lock);
  
  static void lock_get_status(char* out, struct file_lock *fl, int id, char *pfx)
  {
  	struct inode *inode = NULL;
  
  	if (fl->fl_file != NULL)
  		inode = fl->fl_file->f_dentry->d_inode;
  
  	out += sprintf(out, "%d:%s ", id, pfx);
  	if (IS_POSIX(fl)) {
  		out += sprintf(out, "%6s %s ",
  			     (fl->fl_flags & FL_ACCESS) ? "ACCESS" : "POSIX ",
  			     (inode == NULL) ? "*NOINODE*" :
  			     (IS_MANDLOCK(inode) &&
  			      (inode->i_mode & (S_IXGRP | S_ISGID)) == S_ISGID) ?
  			     "MANDATORY" : "ADVISORY ");
  	} else if (IS_FLOCK(fl)) {
  		if (fl->fl_type & LOCK_MAND) {
  			out += sprintf(out, "FLOCK  MSNFS     ");
  		} else {
  			out += sprintf(out, "FLOCK  ADVISORY  ");
  		}
  	} else if (IS_LEASE(fl)) {
  		out += sprintf(out, "LEASE  ");
  		if (fl->fl_type & F_INPROGRESS)
  			out += sprintf(out, "BREAKING  ");
  		else if (fl->fl_file)
  			out += sprintf(out, "ACTIVE    ");
  		else
  			out += sprintf(out, "BREAKER   ");
  	} else {
  		out += sprintf(out, "UNKNOWN UNKNOWN  ");
  	}
  	if (fl->fl_type & LOCK_MAND) {
  		out += sprintf(out, "%s ",
  			       (fl->fl_type & LOCK_READ)
  			       ? (fl->fl_type & LOCK_WRITE) ? "RW   " : "READ "
  			       : (fl->fl_type & LOCK_WRITE) ? "WRITE" : "NONE ");
  	} else {
  		out += sprintf(out, "%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
  		out += sprintf(out, "%d %s:%ld ", fl->fl_pid,
  				inode->i_sb->s_id, inode->i_ino);
  #else
  		/* userspace relies on this representation of dev_t ;-( */
  		out += sprintf(out, "%d %02x:%02x:%ld ", fl->fl_pid,
  				MAJOR(inode->i_sb->s_dev),
  				MINOR(inode->i_sb->s_dev), inode->i_ino);
  #endif
  	} else {
  		out += sprintf(out, "%d <none>:0 ", fl->fl_pid);
  	}
  	if (IS_POSIX(fl)) {
  		if (fl->fl_end == OFFSET_MAX)
  			out += sprintf(out, "%Ld EOF
  ", fl->fl_start);
  		else
  			out += sprintf(out, "%Ld %Ld
  ", fl->fl_start,
  					fl->fl_end);
  	} else {
  		out += sprintf(out, "0 EOF
  ");
  	}
  }
  
  static void move_lock_status(char **p, off_t* pos, off_t offset)
  {
  	int len;
  	len = strlen(*p);
  	if(*pos >= offset) {
  		/* the complete line is valid */
  		*p += len;
  		*pos += len;
  		return;
  	}
  	if(*pos+len > offset) {
  		/* use the second part of the line */
  		int i = offset-*pos;
  		memmove(*p,*p+i,len-i);
  		*p += len-i;
  		*pos += len;
  		return;
  	}
  	/* discard the complete line */
  	*pos += len;
  }
  
  /**
   *	get_locks_status	-	reports lock usage in /proc/locks
   *	@buffer: address in userspace to write into
   *	@start: ?
   *	@offset: how far we are through the buffer
   *	@length: how much to read
   */
  
  int get_locks_status(char *buffer, char **start, off_t offset, int length)
  {
  	struct list_head *tmp;
  	char *q = buffer;
  	off_t pos = 0;
  	int i = 0;
  
  	lock_kernel();
  	list_for_each(tmp, &file_lock_list) {
  		struct list_head *btmp;
  		struct file_lock *fl = list_entry(tmp, struct file_lock, fl_link);
  		lock_get_status(q, fl, ++i, "");
  		move_lock_status(&q, &pos, offset);
  
  		if(pos >= offset+length)
  			goto done;
  
  		list_for_each(btmp, &fl->fl_block) {
  			struct file_lock *bfl = list_entry(btmp,
  					struct file_lock, fl_block);
  			lock_get_status(q, bfl, i, " ->");
  			move_lock_status(&q, &pos, offset);
  
  			if(pos >= offset+length)
  				goto done;
  		}
  	}
  done:
  	unlock_kernel();
  	*start = buffer;
  	if(q-buffer < length)
  		return (q-buffer);
  	return length;
  }
  
  /**
   *	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_kernel();
  	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_kernel();
  	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_kernel();
  	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_kernel();
  	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,
  			init_once, NULL);
  	return 0;
  }
  
  core_initcall(filelock_init);