FreeBSD/Linux Kernel Cross Reference
sys/fs/locks.c

     /*
      *  linux/fs/locks.c
      *
      *  Provide support for fcntl()'s F_GETLK, F_SETLK, and F_SETLKW calls.
      *  Doug Evans (dje@spiff.uucp), August 07, 1992
      *
      *  Deadlock detection added.
      *  FIXME: one thing isn't handled yet:
      *      - mandatory locks (requires lots of changes elsewhere)
     *  Kelly Carmichael (kelly@[142.24.8.65]), September 17, 1994.
     *
     *  Miscellaneous edits, and a total rewrite of posix_lock_file() code.
     *  Kai Petzke (wpp@marie.physik.tu-berlin.de), 1994
     *  
     *  Converted file_lock_table to a linked list from an array, which eliminates
     *  the limits on how many active file locks are open.
     *  Chad Page (pageone@netcom.com), November 27, 1994
     * 
     *  Removed dependency on file descriptors. dup()'ed file descriptors now
     *  get the same locks as the original file descriptors, and a close() on
     *  any file descriptor removes ALL the locks on the file for the current
     *  process. Since locks still depend on the process id, locks are inherited
     *  after an exec() but not after a fork(). This agrees with POSIX, and both
     *  BSD and SVR4 practice.
     *  Andy Walker (andy@lysaker.kvaerner.no), February 14, 1995
     *
     *  Scrapped free list which is redundant now that we allocate locks
     *  dynamically with kmalloc()/kfree().
     *  Andy Walker (andy@lysaker.kvaerner.no), February 21, 1995
     *
     *  Implemented two lock personalities - FL_FLOCK and FL_POSIX.
     *
     *  FL_POSIX locks are created with calls to fcntl() and lockf() through the
     *  fcntl() system call. They have the semantics described above.
     *
     *  FL_FLOCK locks are created with calls to flock(), through the flock()
     *  system call, which is new. Old C libraries implement flock() via fcntl()
     *  and will continue to use the old, broken implementation.
     *
     *  FL_FLOCK locks follow the 4.4 BSD flock() semantics. They are associated
     *  with a file pointer (filp). As a result they can be shared by a parent
     *  process and its children after a fork(). They are removed when the last
     *  file descriptor referring to the file pointer is closed (unless explicitly
     *  unlocked). 
     *
     *  FL_FLOCK locks never deadlock, an existing lock is always removed before
     *  upgrading from shared to exclusive (or vice versa). When this happens
     *  any processes blocked by the current lock are woken up and allowed to
     *  run before the new lock is applied.
     *  Andy Walker (andy@lysaker.kvaerner.no), June 09, 1995
     *
     *  Removed some race conditions in flock_lock_file(), marked other possible
     *  races. Just grep for FIXME to see them. 
     *  Dmitry Gorodchanin (pgmdsg@ibi.com), February 09, 1996.
     *
     *  Addressed Dmitry's concerns. Deadlock checking no longer recursive.
     *  Lock allocation changed to GFP_ATOMIC as we can't afford to sleep
     *  once we've checked for blocking and deadlocking.
     *  Andy Walker (andy@lysaker.kvaerner.no), April 03, 1996.
     *
     *  Initial implementation of mandatory locks. SunOS turned out to be
     *  a rotten model, so I implemented the "obvious" semantics.
     *  See 'Documentation/filesystems/mandatory-locking.txt' for details.
     *  Andy Walker (andy@lysaker.kvaerner.no), April 06, 1996.
     *
     *  Don't allow mandatory locks on mmap()'ed files. Added simple functions to
     *  check if a file has mandatory locks, used by mmap(), open() and creat() to
     *  see if system call should be rejected. Ref. HP-UX/SunOS/Solaris Reference
     *  Manual, Section 2.
     *  Andy Walker (andy@lysaker.kvaerner.no), April 09, 1996.
     *
     *  Tidied up block list handling. Added '/proc/locks' interface.
     *  Andy Walker (andy@lysaker.kvaerner.no), April 24, 1996.
     *
     *  Fixed deadlock condition for pathological code that mixes calls to
     *  flock() and fcntl().
     *  Andy Walker (andy@lysaker.kvaerner.no), April 29, 1996.
     *
     *  Allow only one type of locking scheme (FL_POSIX or FL_FLOCK) to be in use
     *  for a given file at a time. Changed the CONFIG_LOCK_MANDATORY scheme to
     *  guarantee sensible behaviour in the case where file system modules might
     *  be compiled with different options than the kernel itself.
     *  Andy Walker (andy@lysaker.kvaerner.no), May 15, 1996.
     *
     *  Added a couple of missing wake_up() calls. Thanks to Thomas Meckel
     *  (Thomas.Meckel@mni.fh-giessen.de) for spotting this.
     *  Andy Walker (andy@lysaker.kvaerner.no), May 15, 1996.
     *
     *  Changed FL_POSIX locks to use the block list in the same way as FL_FLOCK
     *  locks. Changed process synchronisation to avoid dereferencing locks that
     *  have already been freed.
     *  Andy Walker (andy@lysaker.kvaerner.no), Sep 21, 1996.
     *
     *  Made the block list a circular list to minimise searching in the list.
     *  Andy Walker (andy@lysaker.kvaerner.no), Sep 25, 1996.
     *
     *  Made mandatory locking a mount option. Default is not to allow mandatory
     *  locking.
     *  Andy Walker (andy@lysaker.kvaerner.no), Oct 04, 1996.
    *
    *  Some adaptations for NFS support.
    *  Olaf Kirch (okir@monad.swb.de), Dec 1996,
    *
    *  Fixed /proc/locks interface so that we can't overrun the buffer we are handed.
    *  Andy Walker (andy@lysaker.kvaerner.no), May 12, 1997.
    *
    *  Use slab allocator instead of kmalloc/kfree.
    *  Use generic list implementation from <linux/list.h>.
    *  Sped up posix_locks_deadlock by only considering blocked locks.
    *  Matthew Wilcox <willy@debian.org>, March, 2000.
    *
    *  Leases and LOCK_MAND
    *  Matthew Wilcox <willy@debian.org>, June, 2000.
    *  Stephen Rothwell <sfr@canb.auug.org.au>, June, 2000.
    */
   
   #include <linux/capability.h>
   #include <linux/file.h>
   #include <linux/fdtable.h>
   #include <linux/fs.h>
   #include <linux/init.h>
   #include <linux/module.h>
   #include <linux/security.h>
   #include <linux/slab.h>
   #include <linux/syscalls.h>
   #include <linux/time.h>
   #include <linux/rcupdate.h>
   #include <linux/pid_namespace.h>
   
   #include <asm/uaccess.h>
   
   #define IS_POSIX(fl)    (fl->fl_flags & FL_POSIX)
   #define IS_FLOCK(fl)    (fl->fl_flags & FL_FLOCK)
   #define IS_LEASE(fl)    (fl->fl_flags & FL_LEASE)
   
   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;
   }
   
   /**
    * posix_lock_file - Apply a POSIX-style lock to a file
    * @filp: The file to apply the lock to
    * @fl: The lock to be applied
    * @conflock: Place to return a copy of the conflicting lock, if found.
    *
    * Add a POSIX style lock to a file.
    * We merge adjacent & overlapping locks whenever possible.
    * POSIX locks are sorted by owner task, then by starting address
    *
    * Note that if called with an FL_EXISTS argument, the caller may determine
    * whether or not a lock was successfully freed by testing the return
   * value for -ENOENT.
   */
  int posix_lock_file(struct file *filp, struct file_lock *fl,
                          struct file_lock *conflock)
  {
          return __posix_lock_file(filp->f_path.dentry->d_inode, fl, conflock);
  }
  EXPORT_SYMBOL(posix_lock_file);
  
  /**
   * posix_lock_file_wait - Apply a POSIX-style lock to a file
   * @filp: The file to apply the lock to
   * @fl: The lock to be applied
   *
   * Add a POSIX style lock to a file.
   * We merge adjacent & overlapping locks whenever possible.
   * POSIX locks are sorted by owner task, then by starting address
   */
  int posix_lock_file_wait(struct file *filp, struct file_lock *fl)
  {
          int error;
          might_sleep ();
          for (;;) {
                  error = posix_lock_file(filp, fl, NULL);
                  if (error != FILE_LOCK_DEFERRED)
                          break;
                  error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
                  if (!error)
                          continue;
  
                  locks_delete_block(fl);
                  break;
          }
          return error;
  }
  EXPORT_SYMBOL(posix_lock_file_wait);
  
  /**
   * locks_mandatory_locked - Check for an active lock
   * @inode: the file to check
   *
   * Searches the inode's list of locks to find any POSIX locks which conflict.
   * This function is called from locks_verify_locked() only.
   */
  int locks_mandatory_locked(struct inode *inode)
  {
          fl_owner_t owner = current->files;
          struct file_lock *fl;
  
          /*
           * Search the lock list for this inode for any POSIX locks.
           */
          lock_flocks();
          for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
                  if (!IS_POSIX(fl))
                          continue;
                  if (fl->fl_owner != owner)
                          break;
          }
          unlock_flocks();
          return fl ? -EAGAIN : 0;
  }
  
  /**
   * locks_mandatory_area - Check for a conflicting lock
   * @read_write: %FLOCK_VERIFY_WRITE for exclusive access, %FLOCK_VERIFY_READ
   *              for shared
   * @inode:      the file to check
   * @filp:       how the file was opened (if it was)
   * @offset:     start of area to check
   * @count:      length of area to check
   *
   * Searches the inode's list of locks to find any POSIX locks which conflict.
   * This function is called from rw_verify_area() and
   * locks_verify_truncate().
   */
  int locks_mandatory_area(int read_write, struct inode *inode,
                           struct file *filp, loff_t offset,
                           size_t count)
  {
          struct file_lock fl;
          int error;
  
          locks_init_lock(&fl);
          fl.fl_owner = current->files;
          fl.fl_pid = current->tgid;
          fl.fl_file = filp;
          fl.fl_flags = FL_POSIX | FL_ACCESS;
          if (filp && !(filp->f_flags & O_NONBLOCK))
                  fl.fl_flags |= FL_SLEEP;
          fl.fl_type = (read_write == FLOCK_VERIFY_WRITE) ? F_WRLCK : F_RDLCK;
          fl.fl_start = offset;
          fl.fl_end = offset + count - 1;
  
          for (;;) {
                  error = __posix_lock_file(inode, &fl, NULL);
                  if (error != FILE_LOCK_DEFERRED)
                          break;
                  error = wait_event_interruptible(fl.fl_wait, !fl.fl_next);
                  if (!error) {
                          /*
                           * If we've been sleeping someone might have
                           * changed the permissions behind our back.
                           */
                          if (__mandatory_lock(inode))
                                  continue;
                  }
  
                  locks_delete_block(&fl);
                  break;
          }
  
          return error;
  }
  
  EXPORT_SYMBOL(locks_mandatory_area);
  
  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;
          }
  }
  
  /**
   *      __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;
          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);
  
  /**
   *      lease_get_mtime - get the last modified time of an inode
   *      @inode: the inode
   *      @time:  pointer to a timespec which will contain the last modified time
   *
   * This is to force NFS clients to flush their caches for files with
   * exclusive leases.  The justification is that if someone has an
   * exclusive lease, then they could be modifying it.
   */
  void lease_get_mtime(struct inode *inode, struct timespec *time)
  {
          struct file_lock *flock = inode->i_flock;
          if (flock && IS_LEASE(flock) && (flock->fl_type == F_WRLCK))
                  *time = current_fs_time(inode->i_sb);
          else
                  *time = inode->i_mtime;
  }
  
  EXPORT_SYMBOL(lease_get_mtime);
  
  /**
   *      fcntl_getlease - Enquire what lease is currently active
   *      @filp: the file
   *
   *      The value returned by this function will be one of
   *      (if no lease break is pending):
   *
   *      %F_RDLCK to indicate a shared lease is held.
   *
   *      %F_WRLCK to indicate an exclusive lease is held.
   *
   *      %F_UNLCK to indicate no lease is held.
   *
   *      (if a lease break is pending):
   *
   *      %F_RDLCK to indicate an exclusive lease needs to be
   *              changed to a shared lease (or removed).
   *
   *      %F_UNLCK to indicate the lease needs to be removed.
   *
   *      XXX: sfr & willy disagree over whether F_INPROGRESS
   *      should be returned to userspace.
   */
  int fcntl_getlease(struct file *filp)
  {
          struct file_lock *fl;
          int type = F_UNLCK;
  
          lock_flocks();
          time_out_leases(filp->f_path.dentry->d_inode);
          for (fl = filp->f_path.dentry->d_inode->i_flock; fl && IS_LEASE(fl);
                          fl = fl->fl_next) {
                  if (fl->fl_file == filp) {
                          type = 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;
  }
  
  /**
   *      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->lm_break function is required
   *      by break_lease().
   *
   *      Called with file_lock_lock held.
   */
  int generic_setlease(struct file *filp, long arg, struct file_lock **flp)
  {
          struct 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);
  }
  
  /**
   *      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->lm_break operation must be set; if not,
   *      break_lease will oops!
   *
   *      This will call the filesystem's setlease file method, if
   *      defined.  Note that there is no getlease method; instead, the
   *      filesystem setlease method should call back to setlease() to
   *      add a lease to the inode's lease list, where fcntl_getlease() can
   *      find it.  Since fcntl_getlease() only reports whether the current
   *      task holds a lease, a cluster filesystem need only do this for
   *      leases held by processes on this node.
   *
   *      There is also no break_lease method; filesystems that
   *      handle their own leases should break leases themselves from the
   *      filesystem's open, create, and (on truncate) setattr methods.
   *
   *      Warning: the only current setlease methods exist only to disable
   *      leases in certain cases.  More vfs changes may be required to
   *      allow a full filesystem lease implementation.
   */
  
  int vfs_setlease(struct file *filp, long arg, struct file_lock **lease)
  {
          int error;
  
          lock_flocks();
          error = __vfs_setlease(filp, arg, lease);
          unlock_flocks();
  
          return error;
  }
  EXPORT_SYMBOL_GPL(vfs_setlease);
  
  static int do_fcntl_delete_lease(struct file *filp)
  {
          struct file_lock fl, *flp = &fl;
  
          lease_init(filp, F_UNLCK, flp);
  
          return vfs_setlease(filp, F_UNLCK, &flp);
  }
  
  static int do_fcntl_add_lease(unsigned int fd, struct file *filp, long arg)
  {
          struct file_lock *fl, *ret;
          struct fasync_struct *new;
          int error;
  
          fl = lease_alloc(filp, arg);
          if (IS_ERR(fl))
                  return PTR_ERR(fl);
  
          new = fasync_alloc();
          if (!new) {
                  locks_free_lock(fl);
                  return -ENOMEM;
          }
          ret = fl;
          lock_flocks();
          error = __vfs_setlease(filp, arg, &ret);
          if (error) {
                  unlock_flocks();
                  locks_free_lock(fl);
                  goto out_free_fasync;
          }
          if (ret != fl)
                  locks_free_lock(fl);
  
          /*
           * fasync_insert_entry() returns the old entry if any.
           * If there was no old entry, then it used 'new' and
           * inserted it into the fasync list. Clear new so that
           * we don't release it here.
           */
          if (!fasync_insert_entry(fd, filp, &ret->fl_fasync, new))
                  new = NULL;
  
          error = __f_setown(filp, task_pid(current), PIDTYPE_PID, 0);
          unlock_flocks();
  
  out_free_fasync:
          if (new)
                  fasync_free(new);
          return error;
  }
  
  /**
   *      fcntl_setlease  -       sets a lease on an open file
   *      @fd: open file descriptor
   *      @filp: file pointer
   *      @arg: type of lease to obtain
   *
   *      Call this fcntl to establish a lease on the file.
   *      Note that you also need to call %F_SETSIG to
   *      receive a signal when the lease is broken.
   */
  int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
  {
          if (arg == F_UNLCK)
                  return do_fcntl_delete_lease(filp);
          return do_fcntl_add_lease(fd, filp, arg);
  }
  
  /**
   * flock_lock_file_wait - Apply a FLOCK-style lock to a file
   * @filp: The file to apply the lock to
   * @fl: The lock to be applied
   *
   * Add a FLOCK style lock to a file.
   */
  int flock_lock_file_wait(struct file *filp, struct file_lock *fl)
  {
          int error;
          might_sleep();
          for (;;) {
                  error = flock_lock_file(filp, fl);
                  if (error != FILE_LOCK_DEFERRED)
                          break;
                  error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
                  if (!error)
                          continue;
  
                  locks_delete_block(fl);
                  break;
          }
          return error;
  }
  
  EXPORT_SYMBOL(flock_lock_file_wait);
  
  /**
   *      sys_flock: - flock() system call.
   *      @fd: the file descriptor to lock.
   *      @cmd: the type of lock to apply.
   *
   *      Apply a %FL_FLOCK style lock to an open file descriptor.
   *      The @cmd can be one of
   *
   *      %LOCK_SH -- a shared lock.
   *
   *      %LOCK_EX -- an exclusive lock.
   *
   *      %LOCK_UN -- remove an existing lock.
   *
   *      %LOCK_MAND -- a `mandatory' flock.  This exists to emulate Windows Share Modes.
   *
   *      %LOCK_MAND can be combined with %LOCK_READ or %LOCK_WRITE to allow other
   *      processes read and write access respectively.
   */
  SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
  {
          struct 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;
  }
  
  /**
   * 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)
   * lm_grant is set. Callers expecting ->lock() to return asynchronously
   * will only use F_SETLK, not F_SETLKW; they will set FL_SLEEP if (and only if)
   * the request is for a blocking lock. When ->lock() does return asynchronously,
   * it must return FILE_LOCK_DEFERRED, and call ->lm_grant() when the lock
   * request completes.
   * If the request is for non-blocking lock the file system should return
   * FILE_LOCK_DEFERRED then try to get the lock and call the callback routine
   * with the result. If the request timed out the callback routine will return a
   * nonzero return code and the file system should release the lock. The file
   * system is also responsible to keep a corresponding posix lock when it
   * grants a lock so the VFS can find out which locks are locally held and do
   * the correct lock cleanup when required.
   * The underlying filesystem must not drop the kernel lock or call
   * ->lm_grant() before returning to the caller with a FILE_LOCK_DEFERRED
   * return code.
   */
  int vfs_lock_file(struct file *filp, unsigned int cmd, struct file_lock *fl, struct file_lock *conf)
  {
          if (filp->f_op && filp->f_op->lock)
                  return filp->f_op->lock(filp, cmd, fl);
          else
                  return posix_lock_file(filp, fl, conf);
  }
  EXPORT_SYMBOL_GPL(vfs_lock_file);
  
  static int do_lock_file_wait(struct file *filp, unsigned int cmd,
                               struct file_lock *fl)
  {
          int error;
  
          error = security_file_lock(filp, fl->fl_type);
          if (error)
                  return error;
  
          for (;;) {
                  error = vfs_lock_file(filp, cmd, fl, NULL);
                  if (error != FILE_LOCK_DEFERRED)
                          break;
                  error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
                  if (!error)
                          continue;
  
                  locks_delete_block(fl);
                  break;
          }
  
          return error;
  }
  
  /* Apply the lock described by l to an open file descriptor.
   * This implements both the F_SETLK and F_SETLKW commands of fcntl().
   */
  int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd,
                  struct flock __user *l)
  {
          struct file_lock *file_lock = locks_alloc_lock();
          struct flock flock;
          struct inode *inode;
          struct file *f;
          int error;
  
          if (file_lock == NULL)
                  return -ENOLCK;
  
          /*
           * This might block, so we do it before checking the inode.
           */
          error = -EFAULT;
          if (copy_from_user(&flock, l, sizeof(flock)))
                  goto out;
  
          inode = filp->f_path.dentry->d_inode;
  
          /* Don't allow mandatory locks on files that may be memory mapped
           * and shared.
           */
          if (mandatory_lock(inode) && mapping_writably_mapped(filp->f_mapping)) {
                  error = -EAGAIN;
                  goto out;
          }
  
  again:
          error = flock_to_posix_lock(filp, file_lock, &flock);
          if (error)
                  goto out;
          if (cmd == F_SETLKW) {
                  file_lock->fl_flags |= FL_SLEEP;
          }
          
          error = -EBADF;
          switch (flock.l_type) {
          case F_RDLCK:
                  if (!(filp->f_mode & FMODE_READ))
                          goto out;
                  break;
          case F_WRLCK:
                  if (!(filp->f_mode & FMODE_WRITE))
                          goto out;
                  break;
          case F_UNLCK:
                  break;
          default:
                  error = -EINVAL;
                  goto out;
          }
  
          error = do_lock_file_wait(filp, cmd, file_lock);
  
          /*
           * Attempt to detect a close/fcntl race and recover by
           * releasing the lock that was just acquired.
           */
          /*
           * we need that spin_lock here - it prevents reordering between
           * update of inode->i_flock and check for it done in close().
           * rcu_read_lock() wouldn't do.
           */
          spin_lock(&current->files->file_lock);
          f = fcheck(fd);
          spin_unlock(&current->files->file_lock);
          if (!error && f != filp && flock.l_type != F_UNLCK) {
                  flock.l_type = F_UNLCK;
                  goto again;
          }
  
  out:
          locks_free_lock(file_lock);
          return error;
  }
  
  #if BITS_PER_LONG == 32
  /* Report the first existing lock that would conflict with l.
   * This implements the F_GETLK command of fcntl().
   */
  int fcntl_getlk64(struct file *filp, struct flock64 __user *l)
  {
          struct file_lock file_lock;
          struct flock64 flock;
          int error;
  
          error = -EFAULT;
          if (copy_from_user(&flock, l, sizeof(flock)))
                  goto out;
          error = -EINVAL;
          if ((flock.l_type != F_RDLCK) && (flock.l_type != F_WRLCK))
                  goto out;
  
          error = flock64_to_posix_lock(filp, &file_lock, &flock);
          if (error)
                  goto out;
  
          error = vfs_test_lock(filp, &file_lock);
          if (error)
                  goto out;
  
          flock.l_type = file_lock.fl_type;
          if (file_lock.fl_type != F_UNLCK)
                  posix_lock_to_flock64(&flock, &file_lock);
  
          error = -EFAULT;
          if (!copy_to_user(l, &flock, sizeof(flock)))
                  error = 0;
    
  out:
          return error;
  }
  
  /* Apply the lock described by l to an open file descriptor.
   * This implements both the F_SETLK and F_SETLKW commands of fcntl().
   */
  int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
                  struct flock64 __user *l)
  {
          struct file_lock *file_lock = locks_alloc_lock();
          struct flock64 flock;
          struct inode *inode;
          struct file *f;
          int error;
  
          if (file_lock == NULL)
                  return -ENOLCK;
  
          /*
           * This might block, so we do it before checking the inode.
           */
          error = -EFAULT;
          if (copy_from_user(&flock, l, sizeof(flock)))
                  goto out;
  
          inode = filp->f_path.dentry->d_inode;
  
          /* Don't allow mandatory locks on files that may be memory mapped
           * and shared.
           */
          if (mandatory_lock(inode) && mapping_writably_mapped(filp->f_mapping)) {
                  error = -EAGAIN;
                  goto out;
          }
  
  again:
          error = flock64_to_posix_lock(filp, file_lock, &flock);
          if (error)
                  goto out;
          if (cmd == F_SETLKW64) {
                  file_lock->fl_flags |= FL_SLEEP;
          }
          
          error = -EBADF;
          switch (flock.l_type) {
          case F_RDLCK:
                  if (!(filp->f_mode & FMODE_READ))
                          goto out;
                  break;
          case F_WRLCK:
                  if (!(filp->f_mode & FMODE_WRITE))
                          goto out;
                  break;
          case F_UNLCK:
                  break;
          default:
                  error = -EINVAL;
                  goto out;
          }
  
          error = do_lock_file_wait(filp, cmd, file_lock);
  
          /*
           * Attempt to detect a close/fcntl race and recover by
           * releasing the lock that was just acquired.
           */
          spin_lock(&current->files->file_lock);
          f = fcheck(fd);
          spin_unlock(&current->files->file_lock);
          if (!error && f != filp && flock.l_type != F_UNLCK) {
                  flock.l_type = F_UNLCK;
                  goto again;
          }
  
  out:
          locks_free_lock(file_lock);
          return error;
  }
  #endif /* BITS_PER_LONG == 32 */
  
  /*
   * This function is called when the file is being removed
   * from the task's fd array.  POSIX locks belonging to this task
   * are deleted at this time.
   */
  void locks_remove_posix(struct file *filp, fl_owner_t owner)
  {
          struct file_lock lock;
  
          /*
           * If there are no locks held on this file, we don't need to call
           * posix_lock_file().  Another process could be setting a lock on this
           * file at the same time, but we wouldn't remove that lock anyway.
           */
          if (!filp->f_path.dentry->d_inode->i_flock)
                  return;
  
          lock.fl_type = F_UNLCK;
          lock.fl_flags = FL_POSIX | FL_CLOSE;
          lock.fl_start = 0;
          lock.fl_end = OFFSET_MAX;
          lock.fl_owner = owner;
          lock.fl_pid = current->tgid;
          lock.fl_file = filp;
          lock.fl_ops = NULL;
          lock.fl_lmops = NULL;
  
          vfs_lock_file(filp, F_SETLK, &lock, NULL);
  
          if (lock.fl_ops && lock.fl_ops->fl_release_private)
                  lock.fl_ops->fl_release_private(&lock);
  }
  
  EXPORT_SYMBOL(locks_remove_posix);
  
  /*
   * This function is called on the last close of an open file.
   */
  void locks_remove_flock(struct file *filp)
  {
          struct inode * inode = filp->f_path.dentry->d_inode;
          struct file_lock *fl;
          struct file_lock **before;
  
          if (!inode->i_flock)
                  return;
  
          if (filp->f_op && filp->f_op->flock) {
                  struct file_lock fl = {
                          .fl_pid = current->tgid,
                          .fl_file = filp,
                          .fl_flags = FL_FLOCK,
                          .fl_type = F_UNLCK,
                          .fl_end = OFFSET_MAX,
                  };
                  filp->f_op->flock(filp, F_SETLKW, &fl);
                  if (fl.fl_ops && fl.fl_ops->fl_release_private)
                          fl.fl_ops->fl_release_private(&fl);
          }
  
          lock_flocks();
          before = &inode->i_flock;
  
          while ((fl = *before) != NULL) {
                  if (fl->fl_file == filp) {
                          if (IS_FLOCK(fl)) {
                                  locks_delete_lock(before);
                                  continue;
                          }
                          if (IS_LEASE(fl)) {
                                  lease_modify(before, F_UNLCK);
                                  continue;
                          }
                          /* What? */
                          BUG();
                  }
                  before = &fl->fl_next;
          }
          unlock_flocks();
  }
  
  /**
   *      posix_unblock_lock - stop waiting for a file lock
   *      @filp:   how the file was opened
   *      @waiter: the lock which was waiting
   *
   *      lockd needs to block waiting for locks.
   */
  int
  posix_unblock_lock(struct file *filp, struct file_lock *waiter)
  {
          int status = 0;
  
          lock_flocks();
          if (waiter->fl_next)
                  __locks_delete_block(waiter);
          else
                  status = -ENOENT;
          unlock_flocks();
          return status;
  }
  
  EXPORT_SYMBOL(posix_unblock_lock);
  
  /**
   * vfs_cancel_lock - file byte range unblock lock
   * @filp: The file to apply the unblock to
   * @fl: The lock to be unblocked
   *
   * Used by lock managers to cancel blocked requests
   */
  int vfs_cancel_lock(struct file *filp, struct file_lock *fl)
  {
          if (filp->f_op && filp->f_op->lock)
                  return filp->f_op->lock(filp, F_CANCELLK, fl);
          return 0;
  }
  
  EXPORT_SYMBOL_GPL(vfs_cancel_lock);
  
  #ifdef CONFIG_PROC_FS
  #include <linux/proc_fs.h>
  #include <linux/seq_file.h>
  
  static void lock_get_status(struct seq_file *f, struct file_lock *fl,
                              loff_t id, char *pfx)
  {
          struct inode *inode = NULL;
          unsigned int fl_pid;
  
          if (fl->fl_nspid)
                  fl_pid = pid_vnr(fl->fl_nspid);
          else
                  fl_pid = fl->fl_pid;
  
          if (fl->fl_file != NULL)
                  inode = fl->fl_file->f_path.dentry->d_inode;
  
          seq_printf(f, "%lld:%s ", id, pfx);
          if (IS_POSIX(fl)) {
                  seq_printf(f, "%6s %s ",
                               (fl->fl_flags & FL_ACCESS) ? "ACCESS" : "POSIX ",
                               (inode == NULL) ? "*NOINODE*" :
                               mandatory_lock(inode) ? "MANDATORY" : "ADVISORY ");
          } else if (IS_FLOCK(fl)) {
                  if (fl->fl_type & LOCK_MAND) {
                          seq_printf(f, "FLOCK  MSNFS     ");
                  } else {
                          seq_printf(f, "FLOCK  ADVISORY  ");
                  }
          } else if (IS_LEASE(fl)) {
                  seq_printf(f, "LEASE  ");
                  if (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
  
  /**
   *      lock_may_read - checks that the region is free of locks
   *      @inode: the inode that is being read
   *      @start: the first byte to read
   *      @len: the number of bytes to read
   *
   *      Emulates Windows locking requirements.  Whole-file
   *      mandatory locks (share modes) can prohibit a read and
   *      byte-range POSIX locks can prohibit a read if they overlap.
   *
   *      N.B. this function is only ever called
   *      from knfsd and ownership of locks is never checked.
   */
  int lock_may_read(struct inode *inode, loff_t start, unsigned long len)
  {
          struct file_lock *fl;
          int result = 1;
          lock_flocks();
          for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
                  if (IS_POSIX(fl)) {
                          if (fl->fl_type == F_RDLCK)
                                  continue;
                          if ((fl->fl_end < start) || (fl->fl_start > (start + len)))
                                  continue;
                  } else if (IS_FLOCK(fl)) {
                          if (!(fl->fl_type & LOCK_MAND))
                                  continue;
                          if (fl->fl_type & LOCK_READ)
                                  continue;
                  } else
                          continue;
                  result = 0;
                  break;
          }
          unlock_flocks();
          return result;
  }
  
  EXPORT_SYMBOL(lock_may_read);
  
  /**
   *      lock_may_write - checks that the region is free of locks
   *      @inode: the inode that is being written
   *      @start: the first byte to write
   *      @len: the number of bytes to write
   *
   *      Emulates Windows locking requirements.  Whole-file
   *      mandatory locks (share modes) can prohibit a write and
   *      byte-range POSIX locks can prohibit a write if they overlap.
   *
   *      N.B. this function is only ever called
   *      from knfsd and ownership of locks is never checked.
   */
  int lock_may_write(struct inode *inode, loff_t start, unsigned long len)
  {
          struct file_lock *fl;
          int result = 1;
          lock_flocks();
          for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
                  if (IS_POSIX(fl)) {
                          if ((fl->fl_end < start) || (fl->fl_start > (start + len)))
                                  continue;
                  } else if (IS_FLOCK(fl)) {
                          if (!(fl->fl_type & LOCK_MAND))
                                  continue;
                          if (fl->fl_type & LOCK_WRITE)
                                  continue;
                  } else
                          continue;
                  result = 0;
                  break;
          }
          unlock_flocks();
          return result;
  }
  
  EXPORT_SYMBOL(lock_may_write);
  
  static int __init filelock_init(void)
  {
          filelock_cache = kmem_cache_create("file_lock_cache",
                          sizeof(struct file_lock), 0, SLAB_PANIC, NULL);
  
          return 0;
  }
  
  core_initcall(filelock_init);

Cache object: 9e16b364721ec66e8b3800ceba0cee5f