initial_commit

1 files changed, 2341 insertions, 0 deletions

diff --git a/fs/locks.c b/fs/locks.c
new file mode 100644
index 00000000..b286539d
--- /dev/null
+++ b/fs/locks.c
@@ -0,0 +1,2341 @@
+/*
+ *  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_always(struct file_lock *fl)
+{
+	fl->fl_next = NULL;
+	fl->fl_fasync = NULL;
+	fl->fl_owner = NULL;
+	fl->fl_pid = 0;
+	fl->fl_nspid = NULL;
+	fl->fl_file = NULL;
+	fl->fl_flags = 0;
+	fl->fl_type = 0;
+	fl->fl_start = fl->fl_end = 0;
+}
+
+/* Allocate an empty lock structure. */
+struct file_lock *locks_alloc_lock(void)
+{
+	struct file_lock *fl = kmem_cache_alloc(filelock_cache, GFP_KERNEL);
+
+	if (fl)
+		locks_init_lock_always(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->fl_release_private)
+			fl->fl_lmops->fl_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)
+{
+	INIT_LIST_HEAD(&fl->fl_link);
+	INIT_LIST_HEAD(&fl->fl_block);
+	init_waitqueue_head(&fl->fl_wait);
+	fl->fl_ops = NULL;
+	fl->fl_lmops = NULL;
+	locks_init_lock_always(fl);
+}
+
+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)
+{
+	struct file_lock *lock = (struct file_lock *) foo;
+
+	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)
+		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 = {
+	.fl_break = lease_break_callback,
+	.fl_release_private = lease_release_private_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 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->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_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->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);
+
+	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\n", 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->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++;
+	}
+	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->fl_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->fl_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->fl_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->fl_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)
+ * fl_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 ->fl_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
+ * ->fl_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\n", fl->fl_start);
+		else
+			seq_printf(f, "%Ld %Ld\n", fl->fl_start, fl->fl_end);
+	} else {
+		seq_printf(f, "0 EOF\n");
+	}
+}
+
+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,
+			init_once);
+	return 0;
+}
+
+core_initcall(filelock_init);