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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 struct kmem_cache *filelock_cache __read_mostly;

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

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

}

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

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

void locks_init_lock(struct file_lock *fl)
{
      INIT_LIST_HEAD(&fl->fl_link);
      INIT_LIST_HEAD(&fl->fl_block);
      init_waitqueue_head(&fl->fl_wait);
      fl->fl_next = NULL;
      fl->fl_fasync = NULL;
      fl->fl_owner = NULL;
      fl->fl_pid = 0;
      fl->fl_file = NULL;
      fl->fl_flags = 0;
      fl->fl_type = 0;
      fl->fl_start = fl->fl_end = 0;
      fl->fl_ops = NULL;
      fl->fl_lmops = NULL;
}

EXPORT_SYMBOL(locks_init_lock);

/*
 * Initialises the fields of the file lock which are invariant for
 * free file_locks.
 */
static void init_once(struct kmem_cache *cache, void *foo)
{
      struct file_lock *lock = (struct file_lock *) foo;

      locks_init_lock(lock);
}

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

      switch (l->l_type) {
      case F_RDLCK:
      case F_WRLCK:
      case F_UNLCK:
            fl->fl_type = l->l_type;
            break;
      default:
            return -EINVAL;
      }

      return (0);
}
#endif

/* default lease lock manager operations */
static void lease_break_callback(struct file_lock *fl)
{
      kill_fasync(&fl->fl_fasync, SIGIO, POLL_MSG);
}

static void lease_release_private_callback(struct file_lock *fl)
{
      if (!fl->fl_file)
            return;

      f_delown(fl->fl_file);
      fl->fl_file->f_owner.signum = 0;
}

static int lease_mylease_callback(struct file_lock *fl, struct file_lock *try)
{
      return fl->fl_file == try->fl_file;
}

static struct lock_manager_operations lease_manager_ops = {
      .fl_break = lease_break_callback,
      .fl_release_private = lease_release_private_callback,
      .fl_mylease = lease_mylease_callback,
      .fl_change = lease_modify,
};

/*
 * Initialize a lease, use the default lock manager operations
 */
static int lease_init(struct file *filp, int type, struct file_lock *fl)
 {
      if (assign_type(fl, type) != 0)
            return -EINVAL;

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

      fl->fl_file = filp;
      fl->fl_flags = FL_LEASE;
      fl->fl_start = 0;
      fl->fl_end = OFFSET_MAX;
      fl->fl_ops = NULL;
      fl->fl_lmops = &lease_manager_ops;
      return 0;
}

/* Allocate a file_lock initialised to this type of lease */
static struct file_lock *lease_alloc(struct file *filp, int type)
{
      struct file_lock *fl = locks_alloc_lock();
      int error = -ENOMEM;

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

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

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

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

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

/*
 */
static void locks_delete_block(struct file_lock *waiter)
{
      lock_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;

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

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

      /* 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;
}

void
posix_test_lock(struct file *filp, struct file_lock *fl)
{
      struct file_lock *cfl;

      lock_kernel();
      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);
      else
            fl->fl_type = F_UNLCK;
      unlock_kernel();
      return;
}

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
 *
 * However, the failure of this assumption (also possible in the case of
 * multiple tasks sharing the same open file table) also means there's no
 * guarantee that the loop below will terminate.  As a hack, we give up
 * after a few iterations.
 */

#define MAX_DEADLK_ITERATIONS 10

static int posix_locks_deadlock(struct file_lock *caller_fl,
                        struct file_lock *block_fl)
{
      struct file_lock *fl;
      int i = 0;

next_task:
      if (posix_same_owner(caller_fl, block_fl))
            return 1;
      list_for_each_entry(fl, &blocked_list, fl_link) {
            if (posix_same_owner(fl, block_fl)) {
                  if (i++ > MAX_DEADLK_ITERATIONS)
                        return 0;
                  fl = fl->fl_next;
                  block_fl = fl;
                  goto next_task;
            }
      }
      return 0;
}

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

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

      if (request->fl_type != F_UNLCK) {
            error = -ENOMEM;
            new_fl = locks_alloc_lock();
            if (new_fl == NULL)
                  goto out;
            error = 0;
      }

      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)
            cond_resched();

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)
                  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_kernel();
      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_kernel();
      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 = -EAGAIN;
                  locks_insert_block(fl, request);
                  goto out;
            }
      }

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

      /*
       * Find the first old lock with the same owner as the new lock.
       */
      
      before = &inode->i_flock;

      /* First skip locks owned by other processes.  */
      while ((fl = *before) && (!IS_POSIX(fl) ||
                          !posix_same_owner(request, fl))) {
            before = &fl->fl_next;
      }

      /* Process locks with this owner.  */
      while ((fl = *before) && posix_same_owner(request, fl)) {
            /* Detect adjacent or overlapping regions (if same lock type)
             */
            if (request->fl_type == fl->fl_type) {
                  /* In all comparisons of start vs end, use
                   * "start - 1" rather than "end + 1". If end
                   * is OFFSET_MAX, end + 1 will become negative.
                   */
                  if (fl->fl_end < request->fl_start - 1)
                        goto next_lock;
                  /* If the next lock in the list has entirely bigger
                   * addresses than the new one, insert the lock here.
                   */
                  if (fl->fl_start - 1 > request->fl_end)
                        break;

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

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

      error = 0;
      if (!added) {
            if (request->fl_type == F_UNLCK) {
                  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_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
 * @conflock: Place to return a copy of the conflicting lock, if found.
 *
 * Add a POSIX style lock to a file.
 * We merge adjacent & overlapping locks whenever possible.
 * POSIX locks are sorted by owner task, then by starting address
 *
 * Note that if called with an FL_EXISTS argument, the caller may determine
 * whether or not a lock was successfully freed by testing the return
 * value for -ENOENT.
 */
int posix_lock_file(struct file *filp, struct file_lock *fl,
                  struct file_lock *conflock)
{
      return __posix_lock_file(filp->f_path.dentry->d_inode, fl, conflock);
}
EXPORT_SYMBOL(posix_lock_file);

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

            locks_delete_block(&fl);
            break;
      }

      return error;
}

EXPORT_SYMBOL(locks_mandatory_area);

/* We already had a lease on this file; just change its type */
int lease_modify(struct file_lock **before, int arg)
{
      struct file_lock *fl = *before;
      int error = assign_type(fl, arg);

      if (error)
            return error;
      locks_wake_up_blocks(fl);
      if (arg == F_UNLCK)
            locks_delete_lock(before);
      return 0;
}

EXPORT_SYMBOL(lease_modify);

static void time_out_leases(struct inode *inode)
{
      struct file_lock **before;
      struct file_lock *fl;

      before = &inode->i_flock;
      while ((fl = *before) && IS_LEASE(fl) && (fl->fl_type & F_INPROGRESS)) {
            if ((fl->fl_break_time == 0)
                        || time_before(jiffies, fl->fl_break_time)) {
                  before = &fl->fl_next;
                  continue;
            }
            lease_modify(before, fl->fl_type & ~F_INPROGRESS);
            if (fl == *before)      /* lease_modify may have freed fl */
                  before = &fl->fl_next;
      }
}

/**
 *    __break_lease     -     revoke all outstanding leases on file
 *    @inode: the inode of the file to return
 *    @mode: the open mode (read or write)
 *
 *    break_lease (inlined for speed) has checked there already is at least
 *    some kind of lock (maybe a lease) on this file.  Leases are broken on
 *    a call to open() or truncate().  This function can sleep unless you
 *    specified %O_NONBLOCK to your open().
 */
int __break_lease(struct inode *inode, unsigned int mode)
{
      int error = 0, future;
      struct file_lock *new_fl, *flock;
      struct file_lock *fl;
      unsigned long break_time;
      int i_have_this_lease = 0;

      new_fl = lease_alloc(NULL, mode & FMODE_WRITE ? F_WRLCK : F_RDLCK);

      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 (IS_ERR(new_fl) && !i_have_this_lease
                  && ((mode & O_NONBLOCK) == 0)) {
            error = PTR_ERR(new_fl);
            goto out;
      }

      break_time = 0;
      if (lease_break_time > 0) {
            break_time = jiffies + lease_break_time * HZ;
            if (break_time == 0)
                  break_time++;     /* so that 0 means no break time */
      }

      for (fl = flock; fl && IS_LEASE(fl); fl = fl->fl_next) {
            if (fl->fl_type != future) {
                  fl->fl_type = future;
                  fl->fl_break_time = break_time;
                  /* lease must have lmops break callback */
                  fl->fl_lmops->fl_break(fl);
            }
      }

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

restart:
      break_time = flock->fl_break_time;
      if (break_time != 0) {
            break_time -= jiffies;
            if (break_time == 0)
                  break_time++;
      }
      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 (!IS_ERR(new_fl))
            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_path.dentry->d_inode);
      for (fl = filp->f_path.dentry->d_inode->i_flock; fl && IS_LEASE(fl);
                  fl = fl->fl_next) {
            if (fl->fl_file == filp) {
                  type = fl->fl_type & ~F_INPROGRESS;
                  break;
            }
      }
      unlock_kernel();
      return type;
}

/**
 *    generic_setlease  -     sets a lease on an open file
 *    @filp: file pointer
 *    @arg: type of lease to obtain
 *    @flp: input - file_lock to use, output - file_lock inserted
 *
 *    The (input) flp->fl_lmops->fl_break function is required
 *    by break_lease().
 *
 *    Called with kernel lock held.
 */
int generic_setlease(struct file *filp, long arg, struct file_lock **flp)
{
      struct file_lock *fl, **before, **my_before = NULL, *lease;
      struct file_lock *new_fl = NULL;
      struct dentry *dentry = filp->f_path.dentry;
      struct inode *inode = dentry->d_inode;
      int error, rdlease_count = 0, wrlease_count = 0;

      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;

      time_out_leases(inode);

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

      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;

      error = -ENOMEM;
      new_fl = locks_alloc_lock();
      if (new_fl == NULL)
            goto out;

      /*
       * At this point, we know that if there is an exclusive
       * lease on this file, then we hold it on this filp
       * (otherwise our open of this file would have blocked).
       * And if we are trying to acquire an exclusive lease,
       * then the file is not open by anyone (including us)
       * except for this filp.
       */
      for (before = &inode->i_flock;
                  ((fl = *before) != NULL) && IS_LEASE(fl);
                  before = &fl->fl_next) {
            if (lease->fl_lmops->fl_mylease(fl, lease))
                  my_before = before;
            else if (fl->fl_type == (F_INPROGRESS | F_UNLCK))
                  /*
                   * Someone is in the process of opening this
                   * file for writing so we may not take an
                   * exclusive lease on it.
                   */
                  wrlease_count++;
            else
                  rdlease_count++;
      }

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

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

      error = 0;
      if (arg == F_UNLCK)
            goto out;

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

      locks_copy_lock(new_fl, lease);
      locks_insert_lock(before, new_fl);

      *flp = new_fl;
      return 0;

out:
      if (new_fl != NULL)
            locks_free_lock(new_fl);
      return error;
}
EXPORT_SYMBOL(generic_setlease);

 /**
 *    vfs_setlease        -       sets a lease on an open file
 *    @filp: file pointer
 *    @arg: type of lease to obtain
 *    @lease: file_lock to use
 *
 *    Call this to establish a lease on the file.
 *    The (*lease)->fl_lmops->fl_break operation must be set; if not,
 *    break_lease will oops!
 *
 *    This will call the filesystem's setlease file method, if
 *    defined.  Note that there is no getlease method; instead, the
 *    filesystem setlease method should call back to setlease() to
 *    add a lease to the inode's lease list, where fcntl_getlease() can
 *    find it.  Since fcntl_getlease() only reports whether the current
 *    task holds a lease, a cluster filesystem need only do this for
 *    leases held by processes on this node.
 *
 *    There is also no break_lease method; filesystems that
 *    handle their own leases shoud break leases themselves from the
 *    filesystem's open, create, and (on truncate) setattr methods.
 *
 *    Warning: the only current setlease methods exist only to disable
 *    leases in certain cases.  More vfs changes may be required to
 *    allow a full filesystem lease implementation.
 */

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

      lock_kernel();
      if (filp->f_op && filp->f_op->setlease)
            error = filp->f_op->setlease(filp, arg, lease);
      else
            error = generic_setlease(filp, arg, lease);
      unlock_kernel();

      return error;
}
EXPORT_SYMBOL_GPL(vfs_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_path.dentry;
      struct inode *inode = dentry->d_inode;
      int error;

      locks_init_lock(&fl);
      error = lease_init(filp, arg, &fl);
      if (error)
            return error;

      lock_kernel();

      error = vfs_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, task_pid(current), PIDTYPE_PID, 0);
out_unlock:
      unlock_kernel();
      return error;
}

/**
 * flock_lock_file_wait - Apply a FLOCK-style lock to a file
 * @filp: The file to apply the lock to
 * @fl: The lock to be applied
 *
 * Add a FLOCK style lock to a file.
 */
int flock_lock_file_wait(struct file *filp, struct file_lock *fl)
{
      int error;
      might_sleep();
      for (;;) {
            error = flock_lock_file(filp, fl);
            if ((error != -EAGAIN) || !(fl->fl_flags & FL_SLEEP))
                  break;
            error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
            if (!error)
                  continue;

            locks_delete_block(fl);
            break;
      }
      return error;
}

EXPORT_SYMBOL(flock_lock_file_wait);

/**
 *    sys_flock: - flock() system call.
 *    @fd: the file descriptor to lock.
 *    @cmd: the type of lock to apply.
 *
 *    Apply a %FL_FLOCK style lock to an open file descriptor.
 *    The @cmd can be one of
 *
 *    %LOCK_SH -- a shared lock.
 *
 *    %LOCK_EX -- an exclusive lock.
 *
 *    %LOCK_UN -- remove an existing lock.
 *
 *    %LOCK_MAND -- a `mandatory' flock.  This exists to emulate Windows Share Modes.
 *
 *    %LOCK_MAND can be combined with %LOCK_READ or %LOCK_WRITE to allow other
 *    processes read and write access respectively.
 */
asmlinkage long sys_flock(unsigned int fd, unsigned int cmd)
{
      struct file *filp;
      struct file_lock *lock;
      int can_sleep, unlock;
      int error;

      error = -EBADF;
      filp = fget(fd);
      if (!filp)
            goto out;

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

      if (!unlock && !(cmd & LOCK_MAND) && !(filp->f_mode & 3))
            goto out_putf;

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

      error = security_file_lock(filp, cmd);
      if (error)
            goto out_free;

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

 out_free:
      locks_free_lock(lock);

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

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

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

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

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

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

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

      error = vfs_test_lock(filp, &file_lock);
      if (error)
            goto out;
 
      flock.l_type = file_lock.fl_type;
      if (file_lock.fl_type != F_UNLCK) {
            error = posix_lock_to_flock(&flock, &file_lock);
            if (error)
                  goto out;
      }
      error = -EFAULT;
      if (!copy_to_user(l, &flock, sizeof(flock)))
            error = 0;
out:
      return error;
}

/**
 * vfs_lock_file - file byte range lock
 * @filp: The file to apply the lock to
 * @cmd: type of locking operation (F_SETLK, F_GETLK, etc.)
 * @fl: The lock to be applied
 * @conf: Place to return a copy of the conflicting lock, if found.
 *
 * A caller that doesn't care about the conflicting lock may pass NULL
 * as the final argument.
 *
 * If the filesystem defines a private ->lock() method, then @conf will
 * be left unchanged; so a caller that cares should initialize it to
 * some acceptable default.
 *
 * To avoid blocking kernel daemons, such as lockd, that need to acquire POSIX
 * locks, the ->lock() interface may return asynchronously, before the lock has
 * been granted or denied by the underlying filesystem, if (and only if)
 * fl_grant is set. Callers expecting ->lock() to return asynchronously
 * will only use F_SETLK, not F_SETLKW; they will set FL_SLEEP if (and only if)
 * the request is for a blocking lock. When ->lock() does return asynchronously,
 * it must return -EINPROGRESS, and call ->fl_grant() when the lock
 * request completes.
 * If the request is for non-blocking lock the file system should return
 * -EINPROGRESS then try to get the lock and call the callback routine with
 * the result. If the request timed out the callback routine will return a
 * nonzero return code and the file system should release the lock. The file
 * system is also responsible to keep a corresponding posix lock when it
 * grants a lock so the VFS can find out which locks are locally held and do
 * the correct lock cleanup when required.
 * The underlying filesystem must not drop the kernel lock or call
 * ->fl_grant() before returning to the caller with a -EINPROGRESS
 * return code.
 */
int vfs_lock_file(struct file *filp, unsigned int cmd, struct file_lock *fl, struct file_lock *conf)
{
      if (filp->f_op && filp->f_op->lock)
            return filp->f_op->lock(filp, cmd, fl);
      else
            return posix_lock_file(filp, fl, conf);
}
EXPORT_SYMBOL_GPL(vfs_lock_file);

/* 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_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 = security_file_lock(filp, file_lock->fl_type);
      if (error)
            goto out;

      for (;;) {
            error = vfs_lock_file(filp, cmd, file_lock, NULL);
            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 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;
      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 = security_file_lock(filp, file_lock->fl_type);
      if (error)
            goto out;

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

            locks_delete_block(file_lock);
            break;
      }

      /*
       * Attempt to detect a close/fcntl race and recover by
       * releasing the lock that was just acquired.
       */
      if (!error && fcheck(fd) != filp && flock.l_type != F_UNLCK) {
            flock.l_type = F_UNLCK;
            goto again;
      }

out:
      locks_free_lock(file_lock);
      return error;
}
#endif /* BITS_PER_LONG == 32 */

/*
 * This function is called when the file is being removed
 * from the task's fd array.  POSIX locks belonging to this task
 * are deleted at this time.
 */
void locks_remove_posix(struct file *filp, fl_owner_t owner)
{
      struct file_lock lock;

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

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

EXPORT_SYMBOL_GPL(vfs_cancel_lock);

#ifdef CONFIG_PROC_FS
#include <linux/seq_file.h>

static void lock_get_status(struct seq_file *f, struct file_lock *fl,
                                          int id, char *pfx)
{
      struct inode *inode = NULL;

      if (fl->fl_file != NULL)
            inode = fl->fl_file->f_path.dentry->d_inode;

      seq_printf(f, "%d:%s ", id, pfx);
      if (IS_POSIX(fl)) {
            seq_printf(f, "%6s %s ",
                       (fl->fl_flags & FL_ACCESS) ? "ACCESS" : "POSIX ",
                       (inode == NULL) ? "*NOINODE*" :
                       mandatory_lock(inode) ? "MANDATORY" : "ADVISORY ");
      } else if (IS_FLOCK(fl)) {
            if (fl->fl_type & LOCK_MAND) {
                  seq_printf(f, "FLOCK  MSNFS     ");
            } else {
                  seq_printf(f, "FLOCK  ADVISORY  ");
            }
      } else if (IS_LEASE(fl)) {
            seq_printf(f, "LEASE  ");
            if (fl->fl_type & F_INPROGRESS)
                  seq_printf(f, "BREAKING  ");
            else if (fl->fl_file)
                  seq_printf(f, "ACTIVE    ");
            else
                  seq_printf(f, "BREAKER   ");
      } else {
            seq_printf(f, "UNKNOWN UNKNOWN  ");
      }
      if (fl->fl_type & LOCK_MAND) {
            seq_printf(f, "%s ",
                         (fl->fl_type & LOCK_READ)
                         ? (fl->fl_type & LOCK_WRITE) ? "RW   " : "READ "
                         : (fl->fl_type & LOCK_WRITE) ? "WRITE" : "NONE ");
      } else {
            seq_printf(f, "%s ",
                         (fl->fl_type & F_INPROGRESS)
                         ? (fl->fl_type & F_UNLCK) ? "UNLCK" : "READ "
                         : (fl->fl_type & F_WRLCK) ? "WRITE" : "READ ");
      }
      if (inode) {
#ifdef WE_CAN_BREAK_LSLK_NOW
            seq_printf(f, "%d %s:%ld ", fl->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->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->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, (long)f->private, "");

      list_for_each_entry(bfl, &fl->fl_block, fl_block)
            lock_get_status(f, bfl, (long)f->private, " ->");

      f->private++;
      return 0;
}

static void *locks_start(struct seq_file *f, loff_t *pos)
{
      lock_kernel();
      f->private = (void *)1;
      return seq_list_start(&file_lock_list, *pos);
}

static void *locks_next(struct seq_file *f, void *v, loff_t *pos)
{
      return seq_list_next(v, &file_lock_list, pos);
}

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

struct seq_operations locks_seq_operations = {
      .start      = locks_start,
      .next = locks_next,
      .stop = locks_stop,
      .show = locks_show,
};
#endif

/**
 *    lock_may_read - checks that the region is free of locks
 *    @inode: the inode that is being read
 *    @start: the first byte to read
 *    @len: the number of bytes to read
 *
 *    Emulates Windows locking requirements.  Whole-file
 *    mandatory locks (share modes) can prohibit a read and
 *    byte-range POSIX locks can prohibit a read if they overlap.
 *
 *    N.B. this function is only ever called
 *    from knfsd and ownership of locks is never checked.
 */
int lock_may_read(struct inode *inode, loff_t start, unsigned long len)
{
      struct file_lock *fl;
      int result = 1;
      lock_kernel();
      for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
            if (IS_POSIX(fl)) {
                  if (fl->fl_type == F_RDLCK)
                        continue;
                  if ((fl->fl_end < start) || (fl->fl_start > (start + len)))
                        continue;
            } else if (IS_FLOCK(fl)) {
                  if (!(fl->fl_type & LOCK_MAND))
                        continue;
                  if (fl->fl_type & LOCK_READ)
                        continue;
            } else
                  continue;
            result = 0;
            break;
      }
      unlock_kernel();
      return result;
}

EXPORT_SYMBOL(lock_may_read);

/**
 *    lock_may_write - checks that the region is free of locks
 *    @inode: the inode that is being written
 *    @start: the first byte to write
 *    @len: the number of bytes to write
 *
 *    Emulates Windows locking requirements.  Whole-file
 *    mandatory locks (share modes) can prohibit a write and
 *    byte-range POSIX locks can prohibit a write if they overlap.
 *
 *    N.B. this function is only ever called
 *    from knfsd and ownership of locks is never checked.
 */
int lock_may_write(struct inode *inode, loff_t start, unsigned long len)
{
      struct file_lock *fl;
      int result = 1;
      lock_kernel();
      for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
            if (IS_POSIX(fl)) {
                  if ((fl->fl_end < start) || (fl->fl_start > (start + len)))
                        continue;
            } else if (IS_FLOCK(fl)) {
                  if (!(fl->fl_type & LOCK_MAND))
                        continue;
                  if (fl->fl_type & LOCK_WRITE)
                        continue;
            } else
                  continue;
            result = 0;
            break;
      }
      unlock_kernel();
      return result;
}

EXPORT_SYMBOL(lock_may_write);

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

core_initcall(filelock_init);

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