[PATCH] libata: Simplex and other mode filtering logic

[linux-2.6.22.y-op.git] / fs / locks.c

/*
 *  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)
{
        if (fl == NULL) {
                BUG();
                return;
        }
        if (waitqueue_active(&fl->fl_wait))
                panic("Attempting to free lock with active wait queue");

        if (!list_empty(&fl->fl_block))
                panic("Attempting to free lock with active block list");

        if (!list_empty(&fl->fl_link))
                panic("Attempting to free lock on active lock list");

        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)
 {
        fl->fl_owner = current->files;
        fl->fl_pid = current->tgid;

        fl->fl_file = filp;
        fl->fl_flags = FL_LEASE;
        if (assign_type(fl, type) != 0) {
                locks_free_lock(fl);
                return -EINVAL;
        }
        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;

        if (fl == NULL)
                return -ENOMEM;

        error = lease_init(filp, type, fl);
        if (error)
                return error;
        *flp = fl;
        return 0;
}

/* 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\n", 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
 */
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;
}

EXPORT_SYMBOL(posix_locks_deadlock);

/* 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 *new_fl)
{
        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 (new_fl->fl_type == fl->fl_type)
                        goto out;
                found = 1;
                locks_delete_lock(before);
                break;
        }
        unlock_kernel();

        if (new_fl->fl_type == F_UNLCK)
                return 0;

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

        lock_kernel();
        for_each_lock(inode, before) {
                struct file_lock *fl = *before;
                if (IS_POSIX(fl))
                        break;
                if (IS_LEASE(fl))
                        continue;
                if (!flock_locks_conflict(new_fl, fl))
                        continue;
                error = -EAGAIN;
                if (new_fl->fl_flags & FL_SLEEP) {
                        locks_insert_block(fl, new_fl);
                }
                goto out;
        }
        locks_insert_lock(&inode->i_flock, new_fl);
        error = 0;

out:
        unlock_kernel();
        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, *new_fl2;
        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.
         */
        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;

        error = -ENOLCK; /* "no luck" */
        if (!(new_fl && new_fl2))
                goto out;

        /*
         * We've allocated the new locks in advance, so there are no
         * errors possible (and no blocking operations) from here on.
         * 
         * 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;
        }

        error = 0;
        if (!added) {
                if (request->fl_type == F_UNLCK)
                        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) {
                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:
        if (list_empty(&lock->fl_link)) {
                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, **before;

        /*
         * 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.
         */
        before = &filp->f_dentry->d_inode->i_flock;
        if (*before == NULL)
                return;

        lock.fl_type = F_UNLCK;
        lock.fl_flags = FL_POSIX;
        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);
                goto out;
        }

        /* Can't use posix_lock_file here; we need to remove it no matter
         * which pid we have.
         */
        lock_kernel();
        while (*before != NULL) {
                struct file_lock *fl = *before;
                if (IS_POSIX(fl) && posix_same_owner(fl, &lock)) {
                        locks_delete_lock(before);
                        continue;
                }
                before = &fl->fl_next;
        }
        unlock_kernel();
out:
        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\n", fl->fl_start);
                else
                        out += sprintf(out, "%Ld %Ld\n", fl->fl_start,
                                        fl->fl_end);
        } else {
                out += sprintf(out, "0 EOF\n");
        }
}

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 inline void __steal_locks(struct file *file, fl_owner_t from)
{
        struct inode *inode = file->f_dentry->d_inode;
        struct file_lock *fl = inode->i_flock;

        while (fl) {
                if (fl->fl_file == file && fl->fl_owner == from)
                        fl->fl_owner = current->files;
                fl = fl->fl_next;
        }
}

/* When getting ready for executing a binary, we make sure that current
 * has a files_struct on its own. Before dropping the old files_struct,
 * we take over ownership of all locks for all file descriptors we own.
 * Note that we may accidentally steal a lock for a file that a sibling
 * has created since the unshare_files() call.
 */
void steal_locks(fl_owner_t from)
{
        struct files_struct *files = current->files;
        int i, j;
        struct fdtable *fdt;

        if (from == files)
                return;

        lock_kernel();
        j = 0;
        rcu_read_lock();
        fdt = files_fdtable(files);
        for (;;) {
                unsigned long set;
                i = j * __NFDBITS;
                if (i >= fdt->max_fdset || i >= fdt->max_fds)
                        break;
                set = fdt->open_fds->fds_bits[j++];
                while (set) {
                        if (set & 1) {
                                struct file *file = fdt->fd[i];
                                if (file)
                                        __steal_locks(file, from);
                        }
                        i++;
                        set >>= 1;
                }
        }
        rcu_read_unlock();
        unlock_kernel();
}
EXPORT_SYMBOL(steal_locks);

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);