locks.c

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/*
 *  linux/fs/locks.c
 *
 *  Provide support for fcntl()'s F_GETLK, F_SETLK, and F_SETLKW calls.
 *  Doug Evans ([email protected]), 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 ([email protected]), 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 ([email protected]), 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 ([email protected]), February 14, 1995
 *
 *  Scrapped free list which is redundant now that we allocate locks
 *  dynamically with kmalloc()/kfree().
 *  Andy Walker ([email protected]), 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 ([email protected]), June 09, 1995
 *
 *  Removed some race conditions in flock_lock_file(), marked other possible
 *  races. Just grep for FIXME to see them. 
 *  Dmitry Gorodchanin ([email protected]), 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 ([email protected]), April 03, 1996.
 *
 *  Initial implementation of mandatory locks. SunOS turned out to be
 *  a rotten model, so I implemented the "obvious" semantics.
 *  See 'Documentation/filesystems/mandatory-locking.txt' for details.
 *  Andy Walker ([email protected]), 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 ([email protected]), April 09, 1996.
 *
 *  Tidied up block list handling. Added '/proc/locks' interface.
 *  Andy Walker ([email protected]), April 24, 1996.
 *
 *  Fixed deadlock condition for pathological code that mixes calls to
 *  flock() and fcntl().
 *  Andy Walker ([email protected]), 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 ([email protected]), May 15, 1996.
 *
 *  Added a couple of missing wake_up() calls. Thanks to Thomas Meckel
 *  ([email protected]) for spotting this.
 *  Andy Walker ([email protected]), 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 ([email protected]), Sep 21, 1996.
 *
 *  Made the block list a circular list to minimise searching in the list.
 *  Andy Walker ([email protected]), Sep 25, 1996.
 *
 *  Made mandatory locking a mount option. Default is not to allow mandatory
 *  locking.
 *  Andy Walker ([email protected]), Oct 04, 1996.
 *
 *  Some adaptations for NFS support.
 *  Olaf Kirch ([email protected]), Dec 1996,
 *
 *  Fixed /proc/locks interface so that we can't overrun the buffer we are handed.
 *  Andy Walker ([email protected]), 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 <[email protected]>, March, 2000.
 *
 *  Leases and LOCK_MAND
 *  Matthew Wilcox <[email protected]>, June, 2000.
 *  Stephen Rothwell <[email protected]>, 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)

static bool lease_breaking(struct file_lock *fl)
{
    return fl->fl_flags & (FL_UNLOCK_PENDING | FL_DOWNGRADE_PENDING);
}

static int target_leasetype(struct file_lock *fl)
{
    if (fl->fl_flags & FL_UNLOCK_PENDING)
        return F_UNLCK;
    if (fl->fl_flags & FL_DOWNGRADE_PENDING)
        return F_RDLCK;
    return fl->fl_type;
}

int leases_enable = 1;
int lease_break_time = 45;

#define for_each_lock(inode, lockp) \
    for (lockp = &inode->i_flock; *lockp != NULL; lockp = &(*lockp)->fl_next)

static LIST_HEAD(file_lock_list);
static LIST_HEAD(blocked_list);
static DEFINE_SPINLOCK(file_lock_lock);

/*
 * Protects the two list heads above, plus the inode->i_flock list
 */
void lock_flocks(void)
{
    spin_lock(&file_lock_lock);
}
EXPORT_SYMBOL_GPL(lock_flocks);

void unlock_flocks(void)
{
    spin_unlock(&file_lock_lock);
}
EXPORT_SYMBOL_GPL(unlock_flocks);

static struct kmem_cache *filelock_cache __read_mostly;

static void locks_init_lock_heads(struct file_lock *fl)
{
    INIT_LIST_HEAD(&fl->fl_link);
    INIT_LIST_HEAD(&fl->fl_block);
    init_waitqueue_head(&fl->fl_wait);
}

/* Allocate an empty lock structure. */
struct file_lock *locks_alloc_lock(void)
{
    struct file_lock *fl = kmem_cache_zalloc(filelock_cache, GFP_KERNEL);

    if (fl)
        locks_init_lock_heads(fl);

    return fl;
}
EXPORT_SYMBOL_GPL(locks_alloc_lock);

void locks_release_private(struct file_lock *fl)
{
    if (fl->fl_ops) {
        if (fl->fl_ops->fl_release_private)
            fl->fl_ops->fl_release_private(fl);
        fl->fl_ops = NULL;
    }
    fl->fl_lmops = NULL;

}
EXPORT_SYMBOL_GPL(locks_release_private);

/* Free a lock which is not in use. */
void locks_free_lock(struct file_lock *fl)
{
    BUG_ON(waitqueue_active(&fl->fl_wait));
    BUG_ON(!list_empty(&fl->fl_block));
    BUG_ON(!list_empty(&fl->fl_link));

    locks_release_private(fl);
    kmem_cache_free(filelock_cache, fl);
}
EXPORT_SYMBOL(locks_free_lock);

void locks_init_lock(struct file_lock *fl)
{
    memset(fl, 0, sizeof(struct file_lock));
    locks_init_lock_heads(fl);
}

EXPORT_SYMBOL(locks_init_lock);

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

/*
 * Initialize a new lock from an existing file_lock structure.
 */
void __locks_copy_lock(struct file_lock *new, const struct file_lock *fl)
{
    new->fl_owner = fl->fl_owner;
    new->fl_pid = fl->fl_pid;
    new->fl_file = NULL;
    new->fl_flags = fl->fl_flags;
    new->fl_type = fl->fl_type;
    new->fl_start = fl->fl_start;
    new->fl_end = fl->fl_end;
    new->fl_ops = NULL;
    new->fl_lmops = NULL;
}
EXPORT_SYMBOL(__locks_copy_lock);

void locks_copy_lock(struct file_lock *new, struct file_lock *fl)
{
    locks_release_private(new);

    __locks_copy_lock(new, fl);
    new->fl_file = fl->fl_file;
    new->fl_ops = fl->fl_ops;
    new->fl_lmops = fl->fl_lmops;

    locks_copy_private(new, fl);
}

EXPORT_SYMBOL(locks_copy_lock);

static inline int flock_translate_cmd(int cmd) {
    if (cmd & LOCK_MAND)
        return cmd & (LOCK_MAND | LOCK_RW);
    switch (cmd) {
    case LOCK_SH:
        return F_RDLCK;
    case LOCK_EX:
        return F_WRLCK;
    case LOCK_UN:
        return F_UNLCK;
    }
    return -EINVAL;
}

/* Fill in a file_lock structure with an appropriate FLOCK lock. */
static int flock_make_lock(struct file *filp, struct file_lock **lock,
        unsigned int cmd)
{
    struct file_lock *fl;
    int type = flock_translate_cmd(cmd);
    if (type < 0)
        return type;
    
    fl = locks_alloc_lock();
    if (fl == NULL)
        return -ENOMEM;

    fl->fl_file = filp;
    fl->fl_pid = current->tgid;
    fl->fl_flags = FL_FLOCK;
    fl->fl_type = type;
    fl->fl_end = OFFSET_MAX;
    
    *lock = fl;
    return 0;
}

static int assign_type(struct file_lock *fl, long 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 const struct lock_manager_operations lease_manager_ops = {
    .lm_break = lease_break_callback,
    .lm_change = lease_modify,
};

/*
 * Initialize a lease, use the default lock manager operations
 */
static int lease_init(struct file *filp, long 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, long type)
{
    struct file_lock *fl = locks_alloc_lock();
    int error = -ENOMEM;

    if (fl == NULL)
        return ERR_PTR(error);

    error = lease_init(filp, type, fl);
    if (error) {
        locks_free_lock(fl);
        return ERR_PTR(error);
    }
    return fl;
}

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

/*
 * Check whether two locks have the same owner.
 */
static int posix_same_owner(struct file_lock *fl1, struct file_lock *fl2)
{
    if (fl1->fl_lmops && fl1->fl_lmops->lm_compare_owner)
        return fl2->fl_lmops == fl1->fl_lmops &&
            fl1->fl_lmops->lm_compare_owner(fl1, fl2);
    return fl1->fl_owner == fl2->fl_owner;
}

/* Remove waiter from blocker's block list.
 * When blocker ends up pointing to itself then the list is empty.
 */
static void __locks_delete_block(struct file_lock *waiter)
{
    list_del_init(&waiter->fl_block);
    list_del_init(&waiter->fl_link);
    waiter->fl_next = NULL;
}

/*
 */
void locks_delete_block(struct file_lock *waiter)
{
    lock_flocks();
    __locks_delete_block(waiter);
    unlock_flocks();
}
EXPORT_SYMBOL(locks_delete_block);

/* Insert waiter into blocker's block list.
 * We use a circular list so that processes can be easily woken up in
 * the order they blocked. The documentation doesn't require this but
 * it seems like the reasonable thing to do.
 */
static void locks_insert_block(struct file_lock *blocker, 
                   struct file_lock *waiter)
{
    BUG_ON(!list_empty(&waiter->fl_block));
    list_add_tail(&waiter->fl_block, &blocker->fl_block);
    waiter->fl_next = blocker;
    if (IS_POSIX(blocker))
        list_add(&waiter->fl_link, &blocked_list);
}

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

        waiter = list_first_entry(&blocker->fl_block,
                struct file_lock, fl_block);
        __locks_delete_block(waiter);
        if (waiter->fl_lmops && waiter->fl_lmops->lm_notify)
            waiter->fl_lmops->lm_notify(waiter);
        else
            wake_up(&waiter->fl_wait);
    }
}

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

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

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

/*
 * Delete a lock and then free it.
 * Wake up processes that are blocked waiting for this lock,
 * notify the FS that the lock has been cleared and
 * finally free the lock.
 */
static void locks_delete_lock(struct file_lock **thisfl_p)
{
    struct file_lock *fl = *thisfl_p;

    *thisfl_p = fl->fl_next;
    fl->fl_next = NULL;
    list_del_init(&fl->fl_link);

    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;
}

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);

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);

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;
}

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);

static void lease_clear_pending(struct file_lock *fl, int arg)
{
    switch (arg) {
    case F_UNLCK:
        fl->fl_flags &= ~FL_UNLOCK_PENDING;
        /* fall through: */
    case F_RDLCK:
        fl->fl_flags &= ~FL_DOWNGRADE_PENDING;
    }
}

/* 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;
    lease_clear_pending(fl, arg);
    locks_wake_up_blocks(fl);
    if (arg == F_UNLCK) {
        struct file *filp = fl->fl_file;

        f_delown(filp);
        filp->f_owner.signum = 0;
        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;
        }
        locks_delete_lock(before);
    }
    return 0;
}

EXPORT_SYMBOL(lease_modify);

static bool past_time(unsigned long then)
{
    if (!then)
        /* 0 is a special value meaning "this never expires": */
        return false;
    return time_after(jiffies, then);
}

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) && lease_breaking(fl)) {
        if (past_time(fl->fl_downgrade_time))
            lease_modify(before, F_RDLCK);
        if (past_time(fl->fl_break_time))
            lease_modify(before, F_UNLCK);
        if (fl == *before)  /* lease_modify may have freed fl */
            before = &fl->fl_next;
    }
}

int __break_lease(struct inode *inode, unsigned int mode)
{
    int error = 0;
    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);
    if (IS_ERR(new_fl))
        return PTR_ERR(new_fl);

    lock_flocks();

    time_out_leases(inode);

    flock = inode->i_flock;
    if ((flock == NULL) || !IS_LEASE(flock))
        goto out;

    if (!locks_conflict(flock, new_fl))
        goto out;

    for (fl = flock; fl && IS_LEASE(fl); fl = fl->fl_next)
        if (fl->fl_owner == current->files)
            i_have_this_lease = 1;

    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 (want_write) {
            if (fl->fl_flags & FL_UNLOCK_PENDING)
                continue;
            fl->fl_flags |= FL_UNLOCK_PENDING;
            fl->fl_break_time = break_time;
        } else {
            if (lease_breaking(flock))
                continue;
            fl->fl_flags |= FL_DOWNGRADE_PENDING;
            fl->fl_downgrade_time = break_time;
        }
        fl->fl_lmops->lm_break(fl);
    }

    if (i_have_this_lease || (mode & O_NONBLOCK)) {
        error = -EWOULDBLOCK;
        goto out;
    }

restart:
    break_time = flock->fl_break_time;
    if (break_time != 0) {
        break_time -= jiffies;
        if (break_time == 0)
            break_time++;
    }
    locks_insert_block(flock, new_fl);
    unlock_flocks();
    error = wait_event_interruptible_timeout(new_fl->fl_wait,
                        !new_fl->fl_next, break_time);
    lock_flocks();
    __locks_delete_block(new_fl);
    if (error >= 0) {
        if (error == 0)
            time_out_leases(inode);
        /*
         * Wait for the next conflicting lease that has not been
         * broken yet
         */
        for (flock = inode->i_flock; flock && IS_LEASE(flock);
                flock = flock->fl_next) {
            if (locks_conflict(new_fl, flock))
                goto restart;
        }
        error = 0;
    }

out:
    unlock_flocks();
    locks_free_lock(new_fl);
    return error;
}

EXPORT_SYMBOL(__break_lease);

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);

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 = target_leasetype(fl);
            break;
        }
    }
    unlock_flocks();
    return type;
}

int generic_add_lease(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;

    lease = *flp;

    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.
     */
    error = -EAGAIN;
    for (before = &inode->i_flock;
            ((fl = *before) != NULL) && IS_LEASE(fl);
            before = &fl->fl_next) {
        if (fl->fl_file == filp) {
            my_before = before;
            continue;
        }
        /*
         * No exclusive leases if someone else has a lease on
         * this file:
         */
        if (arg == F_WRLCK)
            goto out;
        /*
         * Modifying our existing lease is OK, but no getting a
         * new lease if someone else is opening for write:
         */
        if (fl->fl_flags & FL_UNLOCK_PENDING)
            goto out;
    }

    if (my_before != NULL) {
        error = lease->fl_lmops->lm_change(my_before, arg);
        if (!error)
            *flp = *my_before;
        goto out;
    }

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

    locks_insert_lock(before, lease);
    return 0;

out:
    return error;
}

int generic_delete_lease(struct file *filp, struct file_lock **flp)
{
    struct file_lock *fl, **before;
    struct dentry *dentry = filp->f_path.dentry;
    struct inode *inode = dentry->d_inode;

    for (before = &inode->i_flock;
            ((fl = *before) != NULL) && IS_LEASE(fl);
            before = &fl->fl_next) {
        if (fl->fl_file != filp)
            continue;
        return (*flp)->fl_lmops->lm_change(before, F_UNLCK);
    }
    return -EAGAIN;
}

int generic_setlease(struct file *filp, long arg, struct file_lock **flp)
{
    struct dentry *dentry = filp->f_path.dentry;
    struct inode *inode = dentry->d_inode;
    int error;

    if ((!uid_eq(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;

    time_out_leases(inode);

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

    switch (arg) {
    case F_UNLCK:
        return generic_delete_lease(filp, flp);
    case F_RDLCK:
    case F_WRLCK:
        return generic_add_lease(filp, arg, flp);
    default:
        return -EINVAL;
    }
}
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);
}

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;
}

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);
}

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);

SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
{
    struct fd f = fdget(fd);
    struct file_lock *lock;
    int can_sleep, unlock;
    int error;

    error = -EBADF;
    if (!f.file)
        goto out;

    can_sleep = !(cmd & LOCK_NB);
    cmd &= ~LOCK_NB;
    unlock = (cmd == LOCK_UN);

    if (!unlock && !(cmd & LOCK_MAND) &&
        !(f.file->f_mode & (FMODE_READ|FMODE_WRITE)))
        goto out_putf;

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

    error = security_file_lock(f.file, lock->fl_type);
    if (error)
        goto out_free;

    if (f.file->f_op && f.file->f_op->flock)
        error = f.file->f_op->flock(f.file,
                      (can_sleep) ? F_SETLKW : F_SETLK,
                      lock);
    else
        error = flock_lock_file_wait(f.file, lock);

 out_free:
    locks_free_lock(lock);

 out_putf:
    fdput(f);
 out:
    return error;
}

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;
}

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();
}

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);

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 (lease_breaking(fl))
            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 ",
                   (lease_breaking(fl))
                   ? (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

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);

int lock_may_write(struct inode *inode, loff_t start, unsigned long len)
{
    struct file_lock *fl;
    int result = 1;
    lock_flocks();
    for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
        if (IS_POSIX(fl)) {
            if ((fl->fl_end < start) || (fl->fl_start > (start + len)))
                continue;
        } else if (IS_FLOCK(fl)) {
            if (!(fl->fl_type & LOCK_MAND))
                continue;
            if (fl->fl_type & LOCK_WRITE)
                continue;
        } else
            continue;
        result = 0;
        break;
    }
    unlock_flocks();
    return result;
}

EXPORT_SYMBOL(lock_may_write);

static int __init filelock_init(void)
{
    filelock_cache = kmem_cache_create("file_lock_cache",
            sizeof(struct file_lock), 0, SLAB_PANIC, NULL);

    return 0;
}

core_initcall(filelock_init);