Cross-Referenced Linux and Device Driver Code

   /*
    *  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 <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)
 
 LIST_HEAD(file_lock_list);
 
 EXPORT_SYMBOL(file_lock_list);
 
 static LIST_HEAD(blocked_list);
 
 static kmem_cache_t *filelock_cache;
 
 /* Allocate an empty lock structure. */
 static struct file_lock *locks_alloc_lock(void)
 {
         return kmem_cache_alloc(filelock_cache, SLAB_KERNEL);
 }
 
 /* Free a lock which is not in use. */
 static inline void locks_free_lock(struct file_lock *fl)
 {
         if (fl == NULL) {
                 BUG();
                 return;
         }
         if (waitqueue_active(&fl->fl_wait))
                 panic("Attempting to free lock with active wait queue");
 
         if (!list_empty(&fl->fl_block))
                 panic("Attempting to free lock with active block list");
 
         if (!list_empty(&fl->fl_link))
                 panic("Attempting to free lock on active lock list");
 
         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;
         }
 
         kmem_cache_free(filelock_cache, fl);
 }
 
 void locks_init_lock(struct file_lock *fl)
 {
         INIT_LIST_HEAD(&fl->fl_link);
         INIT_LIST_HEAD(&fl->fl_block);
         init_waitqueue_head(&fl->fl_wait);
         fl->fl_next = NULL;
         fl->fl_fasync = NULL;
         fl->fl_owner = NULL;
         fl->fl_pid = 0;
         fl->fl_file = NULL;
         fl->fl_flags = 0;
         fl->fl_type = 0;
         fl->fl_start = fl->fl_end = 0;
         fl->fl_ops = NULL;
         fl->fl_lmops = NULL;
 }
 
 EXPORT_SYMBOL(locks_init_lock);
 
 /*
  * Initialises the fields of the file lock which are invariant for
  * free file_locks.
  */
 static void init_once(void *foo, kmem_cache_t *cache, unsigned long flags)
 {
         struct file_lock *lock = (struct file_lock *) foo;
 
         if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) !=
                                         SLAB_CTOR_CONSTRUCTOR)
                 return;
 
         locks_init_lock(lock);
 }
 
 /*
  * Initialize a new lock from an existing file_lock structure.
  */
 void locks_copy_lock(struct file_lock *new, struct file_lock *fl)
 {
         new->fl_owner = fl->fl_owner;
         new->fl_pid = fl->fl_pid;
         new->fl_file = fl->fl_file;
         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 = fl->fl_ops;
         new->fl_lmops = fl->fl_lmops;
         if (fl->fl_ops && fl->fl_ops->fl_copy_lock)
                 fl->fl_ops->fl_copy_lock(new, fl);
         if (fl->fl_lmops && fl->fl_lmops->fl_copy_lock)
                 fl->fl_lmops->fl_copy_lock(new, fl);
 }
 
 EXPORT_SYMBOL(locks_copy_lock);
 
 static inline int flock_translate_cmd(int cmd) {
         if (cmd & LOCK_MAND)
                 return cmd & (LOCK_MAND | LOCK_RW);
         switch (cmd) {
         case LOCK_SH:
                 return F_RDLCK;
         case LOCK_EX:
                 return F_WRLCK;
         case LOCK_UN:
                 return F_UNLCK;
         }
         return -EINVAL;
 }
 
 /* Fill in a file_lock structure with an appropriate FLOCK lock. */
 static int flock_make_lock(struct file *filp, struct file_lock **lock,
                 unsigned int cmd)
 {
         struct file_lock *fl;
         int type = flock_translate_cmd(cmd);
         if (type < 0)
                 return type;
         
         fl = locks_alloc_lock();
         if (fl == NULL)
                 return -ENOMEM;
 
         fl->fl_file = filp;
         fl->fl_pid = current->tgid;
         fl->fl_flags = FL_FLOCK;
         fl->fl_type = type;
         fl->fl_end = OFFSET_MAX;
         
         *lock = fl;
         return 0;
 }
 
 static int assign_type(struct file_lock *fl, int type)
 {
         switch (type) {
         case F_RDLCK:
         case F_WRLCK:
         case F_UNLCK:
                 fl->fl_type = type;
                 break;
         default:
                 return -EINVAL;
         }
         return 0;
 }
 
 /* Verify a "struct flock" and copy it to a "struct file_lock" as a POSIX
  * style lock.
  */
 static int flock_to_posix_lock(struct file *filp, struct file_lock *fl,
                                struct flock *l)
 {
         off_t start, end;
 
         switch (l->l_whence) {
         case 0: /*SEEK_SET*/
                 start = 0;
                 break;
         case 1: /*SEEK_CUR*/
                 start = filp->f_pos;
                 break;
         case 2: /*SEEK_END*/
                 start = i_size_read(filp->f_dentry->d_inode);
                 break;
         default:
                 return -EINVAL;
         }
 
         /* POSIX-1996 leaves the case l->l_len < 0 undefined;
            POSIX-2001 defines it. */
         start += l->l_start;
         end = start + l->l_len - 1;
         if (l->l_len < 0) {
                 end = start - 1;
                 start += l->l_len;
         }
 
         if (start < 0)
                 return -EINVAL;
         if (l->l_len > 0 && end < 0)
                 return -EOVERFLOW;
 
         fl->fl_start = start;   /* we record the absolute position */
         fl->fl_end = end;
         if (l->l_len == 0)
                 fl->fl_end = OFFSET_MAX;
         
         fl->fl_owner = current->files;
         fl->fl_pid = current->tgid;
         fl->fl_file = filp;
         fl->fl_flags = FL_POSIX;
         fl->fl_ops = NULL;
         fl->fl_lmops = NULL;
 
         return assign_type(fl, l->l_type);
 }
 
 #if BITS_PER_LONG == 32
 static int flock64_to_posix_lock(struct file *filp, struct file_lock *fl,
                                  struct flock64 *l)
 {
         loff_t start;
 
         switch (l->l_whence) {
         case 0: /*SEEK_SET*/
                 start = 0;
                 break;
         case 1: /*SEEK_CUR*/
                 start = filp->f_pos;
                 break;
         case 2: /*SEEK_END*/
                 start = i_size_read(filp->f_dentry->d_inode);
                 break;
         default:
                 return -EINVAL;
         }
 
         if (((start += l->l_start) < 0) || (l->l_len < 0))
                 return -EINVAL;
         fl->fl_end = start + l->l_len - 1;
         if (l->l_len > 0 && fl->fl_end < 0)
                 return -EOVERFLOW;
         fl->fl_start = start;   /* we record the absolute position */
         if (l->l_len == 0)
                 fl->fl_end = OFFSET_MAX;
         
         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;
 }
 
 struct lock_manager_operations lease_manager_ops = {
         .fl_break = lease_break_callback,
         .fl_release_private = lease_release_private_callback,
 };
 
 /*
  * Initialize a lease, use the default lock manager operations
  */
 static int lease_init(struct file *filp, int type, struct file_lock *fl)
  {
         fl->fl_owner = current->files;
         fl->fl_pid = current->tgid;
 
         fl->fl_file = filp;
         fl->fl_flags = FL_LEASE;
         if (assign_type(fl, type) != 0) {
                 locks_free_lock(fl);
                 return -EINVAL;
         }
         fl->fl_start = 0;
         fl->fl_end = OFFSET_MAX;
         fl->fl_ops = NULL;
         fl->fl_lmops = &lease_manager_ops;
         return 0;
 }
 
 /* Allocate a file_lock initialised to this type of lease */
 static int lease_alloc(struct file *filp, int type, struct file_lock **flp)
 {
         struct file_lock *fl = locks_alloc_lock();
         int error;
 
         if (fl == NULL)
                 return -ENOMEM;
 
         error = lease_init(filp, type, fl);
         if (error)
                 return error;
         *flp = fl;
         return 0;
 }
 
 /* Check if two locks overlap each other.
  */
 static inline int locks_overlap(struct file_lock *fl1, struct file_lock *fl2)
 {
         return ((fl1->fl_end >= fl2->fl_start) &&
                 (fl2->fl_end >= fl1->fl_start));
 }
 
 /*
  * Check whether two locks have the same owner.
  */
 static inline 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 inline 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)
 {
         if (!list_empty(&waiter->fl_block)) {
                 printk(KERN_ERR "locks_insert_block: removing duplicated lock "
                         "(pid=%d %Ld-%Ld type=%d)\n", waiter->fl_pid,
                         waiter->fl_start, waiter->fl_end, waiter->fl_type);
                 __locks_delete_block(waiter);
         }
         list_add_tail(&waiter->fl_block, &blocker->fl_block);
         waiter->fl_next = blocker;
         if (IS_POSIX(blocker))
                 list_add(&waiter->fl_link, &blocked_list);
 }
 
 /* Wake up processes blocked waiting for blocker.
  * If told to wait then schedule the processes until the block list
  * is empty, otherwise empty the block list ourselves.
  */
 static void locks_wake_up_blocks(struct file_lock *blocker)
 {
         while (!list_empty(&blocker->fl_block)) {
                 struct file_lock *waiter = list_entry(blocker->fl_block.next,
                                 struct file_lock, fl_block);
                 __locks_delete_block(waiter);
                 if (waiter->fl_lmops && waiter->fl_lmops->fl_notify)
                         waiter->fl_lmops->fl_notify(waiter);
                 else
                         wake_up(&waiter->fl_wait);
         }
 }
 
 /* Insert file lock fl into an inode's lock list at the position indicated
  * by pos. At the same time add the lock to the global file lock list.
  */
 static void locks_insert_lock(struct file_lock **pos, struct file_lock *fl)
 {
         list_add(&fl->fl_link, &file_lock_list);
 
         /* insert into file's list */
         fl->fl_next = *pos;
         *pos = fl;
 
         if (fl->fl_ops && fl->fl_ops->fl_insert)
                 fl->fl_ops->fl_insert(fl);
 }
 
 /*
  * Delete a lock and then free it.
  * Wake up processes that are blocked waiting for this lock,
  * notify the FS that the lock has been cleared and
  * finally free the lock.
  */
 static void locks_delete_lock(struct file_lock **thisfl_p)
 {
         struct file_lock *fl = *thisfl_p;
 
         *thisfl_p = fl->fl_next;
         fl->fl_next = NULL;
         list_del_init(&fl->fl_link);
 
         fasync_helper(0, fl->fl_file, 0, &fl->fl_fasync);
         if (fl->fl_fasync != NULL) {
                 printk(KERN_ERR "locks_delete_lock: fasync == %p\n", fl->fl_fasync);
                 fl->fl_fasync = NULL;
         }
 
         if (fl->fl_ops && fl->fl_ops->fl_remove)
                 fl->fl_ops->fl_remove(fl);
 
         locks_wake_up_blocks(fl);
         locks_free_lock(fl);
 }
 
 /* Determine if lock sys_fl blocks lock caller_fl. Common functionality
  * checks for shared/exclusive status of overlapping locks.
  */
 static int locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
 {
         if (sys_fl->fl_type == F_WRLCK)
                 return 1;
         if (caller_fl->fl_type == F_WRLCK)
                 return 1;
         return 0;
 }
 
 /* Determine if lock sys_fl blocks lock caller_fl. POSIX specific
  * checking before calling the locks_conflict().
  */
 static int posix_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
 {
         /* POSIX locks owned by the same process do not conflict with
          * each other.
          */
         if (!IS_POSIX(sys_fl) || posix_same_owner(caller_fl, sys_fl))
                 return (0);
 
         /* Check whether they overlap */
         if (!locks_overlap(caller_fl, sys_fl))
                 return 0;
 
         return (locks_conflict(caller_fl, sys_fl));
 }
 
 /* Determine if lock sys_fl blocks lock caller_fl. FLOCK specific
  * checking before calling the locks_conflict().
  */
 static int flock_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
 {
         /* FLOCK locks referring to the same filp do not conflict with
          * each other.
          */
         if (!IS_FLOCK(sys_fl) || (caller_fl->fl_file == sys_fl->fl_file))
                 return (0);
         if ((caller_fl->fl_type & LOCK_MAND) || (sys_fl->fl_type & LOCK_MAND))
                 return 0;
 
         return (locks_conflict(caller_fl, sys_fl));
 }
 
 static int interruptible_sleep_on_locked(wait_queue_head_t *fl_wait, int timeout)
 {
         int result = 0;
         DECLARE_WAITQUEUE(wait, current);
 
         __set_current_state(TASK_INTERRUPTIBLE);
         add_wait_queue(fl_wait, &wait);
         if (timeout == 0)
                 schedule();
         else
                 result = schedule_timeout(timeout);
         if (signal_pending(current))
                 result = -ERESTARTSYS;
         remove_wait_queue(fl_wait, &wait);
         __set_current_state(TASK_RUNNING);
         return result;
 }
 
 static int locks_block_on_timeout(struct file_lock *blocker, struct file_lock *waiter, int time)
 {
         int result;
         locks_insert_block(blocker, waiter);
         result = interruptible_sleep_on_locked(&waiter->fl_wait, time);
         __locks_delete_block(waiter);
         return result;
 }
 
 struct file_lock *
 posix_test_lock(struct file *filp, struct file_lock *fl)
 {
         struct file_lock *cfl;
 
         lock_kernel();
         for (cfl = filp->f_dentry->d_inode->i_flock; cfl; cfl = cfl->fl_next) {
                 if (!IS_POSIX(cfl))
                         continue;
                 if (posix_locks_conflict(cfl, fl))
                         break;
         }
         unlock_kernel();
 
         return (cfl);
 }
 
 EXPORT_SYMBOL(posix_test_lock);
 
 /* This function tests for deadlock condition before putting a process to
  * sleep. The detection scheme is no longer recursive. Recursive was neat,
  * but dangerous - we risked stack corruption if the lock data was bad, or
  * if the recursion was too deep for any other reason.
  *
  * We rely on the fact that a task can only be on one lock's wait queue
  * at a time. When we find blocked_task on a wait queue we can re-search
  * with blocked_task equal to that queue's owner, until either blocked_task
  * isn't found, or blocked_task is found on a queue owned by my_task.
  *
  * Note: the above assumption may not be true when handling lock requests
  * from a broken NFS client. But broken NFS clients have a lot more to
  * worry about than proper deadlock detection anyway... --okir
  */
 int posix_locks_deadlock(struct file_lock *caller_fl,
                                 struct file_lock *block_fl)
 {
         struct list_head *tmp;
 
 next_task:
         if (posix_same_owner(caller_fl, block_fl))
                 return 1;
         list_for_each(tmp, &blocked_list) {
                 struct file_lock *fl = list_entry(tmp, struct file_lock, fl_link);
                 if (posix_same_owner(fl, block_fl)) {
                         fl = fl->fl_next;
                         block_fl = fl;
                         goto next_task;
                 }
         }
         return 0;
 }
 
 EXPORT_SYMBOL(posix_locks_deadlock);
 
 /* Try to create a FLOCK lock on filp. We always insert new FLOCK locks
  * at the head of the list, but that's secret knowledge known only to
  * flock_lock_file and posix_lock_file.
  */
 static int flock_lock_file(struct file *filp, struct file_lock *new_fl)
 {
         struct file_lock **before;
         struct inode * inode = filp->f_dentry->d_inode;
         int error = 0;
         int found = 0;
 
         lock_kernel();
         for_each_lock(inode, before) {
                 struct file_lock *fl = *before;
                 if (IS_POSIX(fl))
                         break;
                 if (IS_LEASE(fl))
                         continue;
                 if (filp != fl->fl_file)
                         continue;
                 if (new_fl->fl_type == fl->fl_type)
                         goto out;
                 found = 1;
                 locks_delete_lock(before);
                 break;
         }
         unlock_kernel();
 
         if (new_fl->fl_type == F_UNLCK)
                 return 0;
 
         /*
          * If a higher-priority process was blocked on the old file lock,
          * give it the opportunity to lock the file.
          */
         if (found)
                 cond_resched();
 
         lock_kernel();
         for_each_lock(inode, before) {
                 struct file_lock *fl = *before;
                 if (IS_POSIX(fl))
                         break;
                 if (IS_LEASE(fl))
                         continue;
                 if (!flock_locks_conflict(new_fl, fl))
                         continue;
                 error = -EAGAIN;
                 if (new_fl->fl_flags & FL_SLEEP) {
                         locks_insert_block(fl, new_fl);
                 }
                 goto out;
         }
         locks_insert_lock(&inode->i_flock, new_fl);
         error = 0;
 
 out:
         unlock_kernel();
         return error;
 }
 
 EXPORT_SYMBOL(posix_lock_file);
 
 static int __posix_lock_file(struct inode *inode, struct file_lock *request)
 {
         struct file_lock *fl;
         struct file_lock *new_fl, *new_fl2;
         struct file_lock *left = NULL;
         struct file_lock *right = NULL;
         struct file_lock **before;
         int error, added = 0;
 
         /*
          * We may need two file_lock structures for this operation,
          * so we get them in advance to avoid races.
          */
         new_fl = locks_alloc_lock();
         new_fl2 = locks_alloc_lock();
 
         lock_kernel();
         if (request->fl_type != F_UNLCK) {
                 for_each_lock(inode, before) {
                         struct file_lock *fl = *before;
                         if (!IS_POSIX(fl))
                                 continue;
                         if (!posix_locks_conflict(request, fl))
                                 continue;
                         error = -EAGAIN;
                         if (!(request->fl_flags & FL_SLEEP))
                                 goto out;
                         error = -EDEADLK;
                         if (posix_locks_deadlock(request, fl))
                                 goto out;
                         error = -EAGAIN;
                         locks_insert_block(fl, request);
                         goto out;
                 }
         }
 
         /* If we're just looking for a conflict, we're done. */
         error = 0;
         if (request->fl_flags & FL_ACCESS)
                 goto out;
 
         error = -ENOLCK; /* "no luck" */
         if (!(new_fl && new_fl2))
                 goto out;
 
         /*
          * We've allocated the new locks in advance, so there are no
          * errors possible (and no blocking operations) from here on.
          * 
          * Find the first old lock with the same owner as the new lock.
          */
         
         before = &inode->i_flock;
 
         /* First skip locks owned by other processes.  */
         while ((fl = *before) && (!IS_POSIX(fl) ||
                                   !posix_same_owner(request, fl))) {
                 before = &fl->fl_next;
         }
 
         /* Process locks with this owner.  */
         while ((fl = *before) && posix_same_owner(request, fl)) {
                 /* Detect adjacent or overlapping regions (if same lock type)
                  */
                 if (request->fl_type == fl->fl_type) {
                         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 > request->fl_end + 1)
                                 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;
                                 fl->fl_u = request->fl_u;
                                 request = fl;
                                 added = 1;
                         }
                 }
                 /* Go on to next lock.
                  */
         next_lock:
                 before = &fl->fl_next;
         }
 
         error = 0;
         if (!added) {
                 if (request->fl_type == F_UNLCK)
                         goto out;
                 locks_copy_lock(new_fl, request);
                 locks_insert_lock(before, new_fl);
                 new_fl = NULL;
         }
         if (right) {
                 if (left == right) {
                         /* The new lock breaks the old one in two pieces,
                          * so we have to use the second new lock.
                          */
                         left = new_fl2;
                         new_fl2 = NULL;
                         locks_copy_lock(left, right);
                         locks_insert_lock(before, left);
                 }
                 right->fl_start = request->fl_end + 1;
                 locks_wake_up_blocks(right);
         }
         if (left) {
                 left->fl_end = request->fl_start - 1;
                 locks_wake_up_blocks(left);
         }
  out:
         unlock_kernel();
         /*
          * Free any unused locks.
          */
         if (new_fl)
                 locks_free_lock(new_fl);
         if (new_fl2)
                 locks_free_lock(new_fl2);
         return error;
 }
 
 /**
  * posix_lock_file - Apply a POSIX-style lock to a file
  * @filp: The file to apply the lock to
  * @fl: The lock to be applied
  *
  * Add a POSIX style lock to a file.
  * We merge adjacent & overlapping locks whenever possible.
  * POSIX locks are sorted by owner task, then by starting address
  */
 int posix_lock_file(struct file *filp, struct file_lock *fl)
 {
         return __posix_lock_file(filp->f_dentry->d_inode, fl);
 }
 
 /**
  * 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->f_dentry->d_inode, fl);
                 if ((error != -EAGAIN) || !(fl->fl_flags & FL_SLEEP))
                         break;
                 error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
                 if (!error)
                         continue;
 
                 locks_delete_block(fl);
                 break;
         }
         return error;
 }
 EXPORT_SYMBOL(posix_lock_file_wait);
 
 /**
  * locks_mandatory_locked - Check for an active lock
  * @inode: the file to check
  *
  * Searches the inode's list of locks to find any POSIX locks which conflict.
  * This function is called from locks_verify_locked() only.
  */
 int locks_mandatory_locked(struct inode *inode)
 {
         fl_owner_t owner = current->files;
         struct file_lock *fl;
 
         /*
          * Search the lock list for this inode for any POSIX locks.
          */
         lock_kernel();
         for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
                 if (!IS_POSIX(fl))
                         continue;
                 if (fl->fl_owner != owner)
                         break;
         }
         unlock_kernel();
         return fl ? -EAGAIN : 0;
 }
 
 /**
  * locks_mandatory_area - Check for a conflicting lock
  * @read_write: %FLOCK_VERIFY_WRITE for exclusive access, %FLOCK_VERIFY_READ
  *              for shared
  * @inode:      the file to check
  * @filp:       how the file was opened (if it was)
  * @offset:     start of area to check
  * @count:      length of area to check
  *
  * Searches the inode's list of locks to find any POSIX locks which conflict.
  * This function is called from rw_verify_area() and
  * locks_verify_truncate().
  */
 int locks_mandatory_area(int read_write, struct inode *inode,
                          struct file *filp, loff_t offset,
                          size_t count)
 {
         struct file_lock fl;
         int error;
 
         locks_init_lock(&fl);
         fl.fl_owner = current->files;
         fl.fl_pid = current->tgid;
         fl.fl_file = filp;
         fl.fl_flags = FL_POSIX | FL_ACCESS;
         if (filp && !(filp->f_flags & O_NONBLOCK))
                 fl.fl_flags |= FL_SLEEP;
         fl.fl_type = (read_write == FLOCK_VERIFY_WRITE) ? F_WRLCK : F_RDLCK;
         fl.fl_start = offset;
         fl.fl_end = offset + count - 1;
 
         for (;;) {
                 error = __posix_lock_file(inode, &fl);
                 if (error != -EAGAIN)
                         break;
                 if (!(fl.fl_flags & FL_SLEEP))
                         break;
                 error = wait_event_interruptible(fl.fl_wait, !fl.fl_next);
                 if (!error) {
                         /*
                          * If we've been sleeping someone might have
                          * changed the permissions behind our back.
                          */
                         if ((inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
                                 continue;
                 }
 
                 locks_delete_block(&fl);
                 break;
         }
 
         return error;
 }
 
 EXPORT_SYMBOL(locks_mandatory_area);
 
 /* We already had a lease on this file; just change its type */
 static 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;
 }
 
 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;
                 }
                 printk(KERN_INFO "lease broken - owner pid = %d\n", fl->fl_pid);
                 lease_modify(before, fl->fl_type & ~F_INPROGRESS);
                 if (fl == *before)      /* lease_modify may have freed fl */
                         before = &fl->fl_next;
         }
 }
 
  /**
 *       remove_lease - let time_out_leases remove the lease.
 *       @@file_lock: the lease to remove
 */
 void remove_lease(struct file_lock *fl)
 {
         lock_kernel();
         if (!fl || !IS_LEASE(fl))
                 goto out;
         fl->fl_type = F_UNLCK | F_INPROGRESS;
         fl->fl_break_time = jiffies - 10;
         time_out_leases(fl->fl_file->f_dentry->d_inode);
 out:
         unlock_kernel();
 }
 
 EXPORT_SYMBOL(remove_lease);
 
 /**
  *      __break_lease   -       revoke all outstanding leases on file
  *      @inode: the inode of the file to return
  *      @mode: the open mode (read or write)
  *
  *      break_lease (inlined for speed) has checked there already
  *      is a lease on this file.  Leases are broken on a call to open()
  *      or truncate().  This function can sleep unless you
  *      specified %O_NONBLOCK to your open().
  */
 int __break_lease(struct inode *inode, unsigned int mode)
 {
         int error = 0, future;
         struct file_lock *new_fl, *flock;
         struct file_lock *fl;
         int alloc_err;
         unsigned long break_time;
         int i_have_this_lease = 0;
 
         alloc_err = lease_alloc(NULL, mode & FMODE_WRITE ? F_WRLCK : F_RDLCK,
                         &new_fl);
 
         lock_kernel();
 
         time_out_leases(inode);
 
         flock = inode->i_flock;
         if ((flock == NULL) || !IS_LEASE(flock))
                 goto out;
 
         for (fl = flock; fl && IS_LEASE(fl); fl = fl->fl_next)
                 if (fl->fl_owner == current->files)
                         i_have_this_lease = 1;
 
         if (mode & FMODE_WRITE) {
                 /* If we want write access, we have to revoke any lease. */
                 future = F_UNLCK | F_INPROGRESS;
         } else if (flock->fl_type & F_INPROGRESS) {
                 /* If the lease is already being broken, we just leave it */
                 future = flock->fl_type;
         } else if (flock->fl_type & F_WRLCK) {
                 /* Downgrade the exclusive lease to a read-only lease. */
                 future = F_RDLCK | F_INPROGRESS;
         } else {
                 /* the existing lease was read-only, so we can read too. */
                 goto out;
         }
 
         if (alloc_err && !i_have_this_lease && ((mode & O_NONBLOCK) == 0)) {
                 error = alloc_err;
                 goto out;
         }
 
         break_time = 0;
         if (lease_break_time > 0) {
                 break_time = jiffies + lease_break_time * HZ;
                 if (break_time == 0)
                         break_time++;   /* so that 0 means no break time */
         }
 
         for (fl = flock; fl && IS_LEASE(fl); fl = fl->fl_next) {
                 if (fl->fl_type != future) {
                         fl->fl_type = future;
                         fl->fl_break_time = break_time;
                         if (fl->fl_lmops && fl->fl_lmops->fl_break)
                                 fl->fl_lmops->fl_break(fl);
                         else    /* lease must have lmops break callback */
                                 BUG();
                 }
         }
 
         if (i_have_this_lease || (mode & O_NONBLOCK)) {
                 error = -EWOULDBLOCK;
                 goto out;
         }
 
 restart:
         break_time = flock->fl_break_time;
         if (break_time != 0) {
                 break_time -= jiffies;
                 if (break_time == 0)
                         break_time++;
         }
         error = locks_block_on_timeout(flock, new_fl, break_time);
         if (error >= 0) {
                 if (error == 0)
                         time_out_leases(inode);
                 /* Wait for the next lease that has not been broken yet */
                 for (flock = inode->i_flock; flock && IS_LEASE(flock);
                                 flock = flock->fl_next) {
                         if (flock->fl_type & F_INPROGRESS)
                                 goto restart;
                 }
                 error = 0;
         }
 
 out:
         unlock_kernel();
         if (!alloc_err)
                 locks_free_lock(new_fl);
         return error;
 }
 
 EXPORT_SYMBOL(__break_lease);
 
 /**
  *      lease_get_mtime
  *      @inode: the inode
  *      @time:  pointer to a timespec which will contain the last modified time
  *
  * This is to force NFS clients to flush their caches for files with
  * exclusive leases.  The justification is that if someone has an
  * exclusive lease, then they could be modifiying it.
  */
 void lease_get_mtime(struct inode *inode, struct timespec *time)
 {
         struct file_lock *flock = inode->i_flock;
         if (flock && IS_LEASE(flock) && (flock->fl_type & F_WRLCK))
                 *time = current_fs_time(inode->i_sb);
         else
                 *time = inode->i_mtime;
 }
 
 EXPORT_SYMBOL(lease_get_mtime);
 
 /**
  *      fcntl_getlease - Enquire what lease is currently active
  *      @filp: the file
  *
  *      The value returned by this function will be one of
  *      (if no lease break is pending):
  *
  *      %F_RDLCK to indicate a shared lease is held.
  *
  *      %F_WRLCK to indicate an exclusive lease is held.
  *
  *      %F_UNLCK to indicate no lease is held.
  *
  *      (if a lease break is pending):
  *
  *      %F_RDLCK to indicate an exclusive lease needs to be
  *              changed to a shared lease (or removed).
  *
  *      %F_UNLCK to indicate the lease needs to be removed.
  *
  *      XXX: sfr & willy disagree over whether F_INPROGRESS
  *      should be returned to userspace.
  */
 int fcntl_getlease(struct file *filp)
 {
         struct file_lock *fl;
         int type = F_UNLCK;
 
         lock_kernel();
         time_out_leases(filp->f_dentry->d_inode);
         for (fl = filp->f_dentry->d_inode->i_flock; fl && IS_LEASE(fl);
                         fl = fl->fl_next) {
                 if (fl->fl_file == filp) {
                         type = fl->fl_type & ~F_INPROGRESS;
                         break;
                 }
         }
         unlock_kernel();
         return type;
 }
 
 /**
  *      __setlease      -       sets a lease on an open file
  *      @filp: file pointer
  *      @arg: type of lease to obtain
  *      @flp: input - file_lock to use, output - file_lock inserted
  *
  *      The (input) flp->fl_lmops->fl_break function is required
  *      by break_lease().
  *
  *      Called with kernel lock held.
  */
 int __setlease(struct file *filp, long arg, struct file_lock **flp)
 {
         struct file_lock *fl, **before, **my_before = NULL, *lease = *flp;
         struct dentry *dentry = filp->f_dentry;
         struct inode *inode = dentry->d_inode;
         int error, rdlease_count = 0, wrlease_count = 0;
 
         time_out_leases(inode);
 
         error = -EINVAL;
         if (!flp || !(*flp) || !(*flp)->fl_lmops || !(*flp)->fl_lmops->fl_break)
                 goto out;
 
         error = -EAGAIN;
         if ((arg == F_RDLCK) && (atomic_read(&inode->i_writecount) > 0))
                 goto out;
         if ((arg == F_WRLCK)
             && ((atomic_read(&dentry->d_count) > 1)
                 || (atomic_read(&inode->i_count) > 1)))
                 goto out;
 
         /*
          * At this point, we know that if there is an exclusive
          * lease on this file, then we hold it on this filp
          * (otherwise our open of this file would have blocked).
          * And if we are trying to acquire an exclusive lease,
          * then the file is not open by anyone (including us)
          * except for this filp.
          */
         for (before = &inode->i_flock;
                         ((fl = *before) != NULL) && IS_LEASE(fl);
                         before = &fl->fl_next) {
                 if (fl->fl_file == filp)
                         my_before = before;
                 else if (fl->fl_type == (F_INPROGRESS | F_UNLCK))
                         /*
                          * Someone is in the process of opening this
                          * file for writing so we may not take an
                          * exclusive lease on it.
                          */
                         wrlease_count++;
                 else
                         rdlease_count++;
         }
 
         if ((arg == F_RDLCK && (wrlease_count > 0)) ||
             (arg == F_WRLCK && ((rdlease_count + wrlease_count) > 0)))
                 goto out;
 
         if (my_before != NULL) {
                 error = lease_modify(my_before, arg);
                 goto out;
         }
 
         error = 0;
         if (arg == F_UNLCK)
                 goto out;
 
         error = -EINVAL;
         if (!leases_enable)
                 goto out;
 
         error = lease_alloc(filp, arg, &fl);
         if (error)
                 goto out;
 
         locks_copy_lock(fl, lease);
 
         locks_insert_lock(before, fl);
 
         *flp = fl;
 out:
         return error;
 }
 
  /**
  *      setlease        -       sets a lease on an open file
  *      @filp: file pointer
  *      @arg: type of lease to obtain
  *      @lease: file_lock to use
  *
  *      Call this to establish a lease on the file.
  *      The fl_lmops fl_break function is required by break_lease
  */
 
 int setlease(struct file *filp, long arg, struct file_lock **lease)
 {
         struct dentry *dentry = filp->f_dentry;
         struct inode *inode = dentry->d_inode;
         int error;
 
         if ((current->fsuid != inode->i_uid) && !capable(CAP_LEASE))
                 return -EACCES;
         if (!S_ISREG(inode->i_mode))
                 return -EINVAL;
         error = security_file_lock(filp, arg);
         if (error)
                 return error;
 
         lock_kernel();
         error = __setlease(filp, arg, lease);
         unlock_kernel();
 
         return error;
 }
 
 EXPORT_SYMBOL(setlease);
 
 /**
  *      fcntl_setlease  -       sets a lease on an open file
  *      @fd: open file descriptor
  *      @filp: file pointer
  *      @arg: type of lease to obtain
  *
  *      Call this fcntl to establish a lease on the file.
  *      Note that you also need to call %F_SETSIG to
  *      receive a signal when the lease is broken.
  */
 int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
 {
         struct file_lock fl, *flp = &fl;
         struct dentry *dentry = filp->f_dentry;
         struct inode *inode = dentry->d_inode;
         int error;
 
         if ((current->fsuid != inode->i_uid) && !capable(CAP_LEASE))
                 return -EACCES;
         if (!S_ISREG(inode->i_mode))
                 return -EINVAL;
         error = security_file_lock(filp, arg);
         if (error)
                 return error;
 
         locks_init_lock(&fl);
         error = lease_init(filp, arg, &fl);
         if (error)
                 return error;
 
         lock_kernel();
 
         error = __setlease(filp, arg, &flp);
         if (error)
                 goto out_unlock;
 
         error = fasync_helper(fd, filp, 1, &flp->fl_fasync);
         if (error < 0) {
                 /* remove lease just inserted by __setlease */
                 flp->fl_type = F_UNLCK | F_INPROGRESS;
                 flp->fl_break_time = jiffies- 10;
                 time_out_leases(inode);
                 goto out_unlock;
         }
 
         error = f_setown(filp, current->pid, 0);
 out_unlock:
         unlock_kernel();
         return error;
 }
 
 /**
  * flock_lock_file_wait - Apply a FLOCK-style lock to a file
  * @filp: The file to apply the lock to
  * @fl: The lock to be applied
  *
  * Add a FLOCK style lock to a file.
  */
 int flock_lock_file_wait(struct file *filp, struct file_lock *fl)
 {
         int error;
         might_sleep();
         for (;;) {
                 error = flock_lock_file(filp, fl);
                 if ((error != -EAGAIN) || !(fl->fl_flags & FL_SLEEP))
                         break;
                 error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
                 if (!error)
                         continue;
 
                 locks_delete_block(fl);
                 break;
         }
         return error;
 }
 
 EXPORT_SYMBOL(flock_lock_file_wait);
 
 /**
  *      sys_flock: - flock() system call.
  *      @fd: the file descriptor to lock.
  *      @cmd: the type of lock to apply.
  *
  *      Apply a %FL_FLOCK style lock to an open file descriptor.
  *      The @cmd can be one of
  *
  *      %LOCK_SH -- a shared lock.
  *
  *      %LOCK_EX -- an exclusive lock.
  *
  *      %LOCK_UN -- remove an existing lock.
  *
  *      %LOCK_MAND -- a `mandatory' flock.  This exists to emulate Windows Share Modes.
  *
  *      %LOCK_MAND can be combined with %LOCK_READ or %LOCK_WRITE to allow other
  *      processes read and write access respectively.
  */
 asmlinkage long sys_flock(unsigned int fd, unsigned int cmd)
 {
         struct file *filp;
         struct file_lock *lock;
         int can_sleep, unlock;
         int error;
 
         error = -EBADF;
         filp = fget(fd);
         if (!filp)
                 goto out;
 
         can_sleep = !(cmd & LOCK_NB);
         cmd &= ~LOCK_NB;
         unlock = (cmd == LOCK_UN);
 
         if (!unlock && !(cmd & LOCK_MAND) && !(filp->f_mode & 3))
                 goto out_putf;
 
         error = flock_make_lock(filp, &lock, cmd);
         if (error)
                 goto out_putf;
         if (can_sleep)
                 lock->fl_flags |= FL_SLEEP;
 
         error = security_file_lock(filp, cmd);
         if (error)
                 goto out_free;
 
         if (filp->f_op && filp->f_op->flock)
                 error = filp->f_op->flock(filp,
                                           (can_sleep) ? F_SETLKW : F_SETLK,
                                           lock);
         else
                 error = flock_lock_file_wait(filp, lock);
 
  out_free:
         if (list_empty(&lock->fl_link)) {
                 locks_free_lock(lock);
         }
 
  out_putf:
         fput(filp);
  out:
         return error;
 }
 
 /* Report the first existing lock that would conflict with l.
  * This implements the F_GETLK command of fcntl().
  */
 int fcntl_getlk(struct file *filp, struct flock __user *l)
 {
         struct file_lock *fl, file_lock;
         struct flock flock;
         int error;
 
         error = -EFAULT;
         if (copy_from_user(&flock, l, sizeof(flock)))
                 goto out;
         error = -EINVAL;
         if ((flock.l_type != F_RDLCK) && (flock.l_type != F_WRLCK))
                 goto out;
 
         error = flock_to_posix_lock(filp, &file_lock, &flock);
         if (error)
                 goto out;
 
         if (filp->f_op && filp->f_op->lock) {
                 error = filp->f_op->lock(filp, F_GETLK, &file_lock);
                 if (error < 0)
                         goto out;
                 else
                   fl = (file_lock.fl_type == F_UNLCK ? NULL : &file_lock);
         } else {
                 fl = posix_test_lock(filp, &file_lock);
         }
  
         flock.l_type = F_UNLCK;
         if (fl != NULL) {
                 flock.l_pid = fl->fl_pid;
 #if BITS_PER_LONG == 32
                 /*
                  * Make sure we can represent the posix lock via
                  * legacy 32bit flock.
                  */
                 error = -EOVERFLOW;
                 if (fl->fl_start > OFFT_OFFSET_MAX)
                         goto out;
                 if ((fl->fl_end != OFFSET_MAX)
                     && (fl->fl_end > OFFT_OFFSET_MAX))
                         goto out;
 #endif
                 flock.l_start = fl->fl_start;
                 flock.l_len = fl->fl_end == OFFSET_MAX ? 0 :
                         fl->fl_end - fl->fl_start + 1;
                 flock.l_whence = 0;
                 flock.l_type = fl->fl_type;
         }
         error = -EFAULT;
         if (!copy_to_user(l, &flock, sizeof(flock)))
                 error = 0;
 out:
         return error;
 }
 
 /* Apply the lock described by l to an open file descriptor.
  * This implements both the F_SETLK and F_SETLKW commands of fcntl().
  */
 int fcntl_setlk(struct file *filp, unsigned int cmd, struct flock __user *l)
 {
         struct file_lock *file_lock = locks_alloc_lock();
         struct flock flock;
         struct inode *inode;
         int error;
 
         if (file_lock == NULL)
                 return -ENOLCK;
 
         /*
          * This might block, so we do it before checking the inode.
          */
         error = -EFAULT;
         if (copy_from_user(&flock, l, sizeof(flock)))
                 goto out;
 
         inode = filp->f_dentry->d_inode;
 
         /* Don't allow mandatory locks on files that may be memory mapped
          * and shared.
          */
         if (IS_MANDLOCK(inode) &&
             (inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID &&
             mapping_writably_mapped(filp->f_mapping)) {
                 error = -EAGAIN;
                 goto out;
         }
 
         error = flock_to_posix_lock(filp, file_lock, &flock);
         if (error)
                 goto out;
         if (cmd == F_SETLKW) {
                 file_lock->fl_flags |= FL_SLEEP;
         }
         
         error = -EBADF;
         switch (flock.l_type) {
         case F_RDLCK:
                 if (!(filp->f_mode & FMODE_READ))
                         goto out;
                 break;
         case F_WRLCK:
                 if (!(filp->f_mode & FMODE_WRITE))
                         goto out;
                 break;
         case F_UNLCK:
                 break;
         default:
                 error = -EINVAL;
                 goto out;
         }
 
         error = security_file_lock(filp, file_lock->fl_type);
         if (error)
                 goto out;
 
         if (filp->f_op && filp->f_op->lock != NULL) {
                 error = filp->f_op->lock(filp, cmd, file_lock);
                 goto out;
         }
 
         for (;;) {
                 error = __posix_lock_file(inode, file_lock);
                 if ((error != -EAGAIN) || (cmd == F_SETLK))
                         break;
                 error = wait_event_interruptible(file_lock->fl_wait,
                                 !file_lock->fl_next);
                 if (!error)
                         continue;
 
                 locks_delete_block(file_lock);
                 break;
         }
 
  out:
         locks_free_lock(file_lock);
         return error;
 }
 
 #if BITS_PER_LONG == 32
 /* Report the first existing lock that would conflict with l.
  * This implements the F_GETLK command of fcntl().
  */
 int fcntl_getlk64(struct file *filp, struct flock64 __user *l)
 {
         struct file_lock *fl, file_lock;
         struct flock64 flock;
         int error;
 
         error = -EFAULT;
         if (copy_from_user(&flock, l, sizeof(flock)))
                 goto out;
         error = -EINVAL;
         if ((flock.l_type != F_RDLCK) && (flock.l_type != F_WRLCK))
                 goto out;
 
         error = flock64_to_posix_lock(filp, &file_lock, &flock);
         if (error)
                 goto out;
 
         if (filp->f_op && filp->f_op->lock) {
                 error = filp->f_op->lock(filp, F_GETLK, &file_lock);
                 if (error < 0)
                         goto out;
                 else
                   fl = (file_lock.fl_type == F_UNLCK ? NULL : &file_lock);
         } else {
                 fl = posix_test_lock(filp, &file_lock);
         }
  
         flock.l_type = F_UNLCK;
         if (fl != NULL) {
                 flock.l_pid = fl->fl_pid;
                 flock.l_start = fl->fl_start;
                 flock.l_len = fl->fl_end == OFFSET_MAX ? 0 :
                         fl->fl_end - fl->fl_start + 1;
                 flock.l_whence = 0;
                 flock.l_type = fl->fl_type;
         }
         error = -EFAULT;
         if (!copy_to_user(l, &flock, sizeof(flock)))
                 error = 0;
   
 out:
         return error;
 }
 
 /* Apply the lock described by l to an open file descriptor.
  * This implements both the F_SETLK and F_SETLKW commands of fcntl().
  */
 int fcntl_setlk64(struct file *filp, unsigned int cmd, struct flock64 __user *l)
 {
         struct file_lock *file_lock = locks_alloc_lock();
         struct flock64 flock;
         struct inode *inode;
         int error;
 
         if (file_lock == NULL)
                 return -ENOLCK;
 
         /*
          * This might block, so we do it before checking the inode.
          */
         error = -EFAULT;
         if (copy_from_user(&flock, l, sizeof(flock)))
                 goto out;
 
         inode = filp->f_dentry->d_inode;
 
         /* Don't allow mandatory locks on files that may be memory mapped
          * and shared.
          */
         if (IS_MANDLOCK(inode) &&
             (inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID &&
             mapping_writably_mapped(filp->f_mapping)) {
                 error = -EAGAIN;
                 goto out;
         }
 
         error = flock64_to_posix_lock(filp, file_lock, &flock);
         if (error)
                 goto out;
         if (cmd == F_SETLKW64) {
                 file_lock->fl_flags |= FL_SLEEP;
         }
         
         error = -EBADF;
         switch (flock.l_type) {
         case F_RDLCK:
                 if (!(filp->f_mode & FMODE_READ))
                         goto out;
                 break;
         case F_WRLCK:
                 if (!(filp->f_mode & FMODE_WRITE))
                         goto out;
                 break;
         case F_UNLCK:
                 break;
         default:
                 error = -EINVAL;
                 goto out;
         }
 
         error = security_file_lock(filp, file_lock->fl_type);
         if (error)
                 goto out;
 
         if (filp->f_op && filp->f_op->lock != NULL) {
                 error = filp->f_op->lock(filp, cmd, file_lock);
                 goto out;
         }
 
         for (;;) {
                 error = __posix_lock_file(inode, file_lock);
                 if ((error != -EAGAIN) || (cmd == F_SETLK64))
                         break;
                 error = wait_event_interruptible(file_lock->fl_wait,
                                 !file_lock->fl_next);
                 if (!error)
                         continue;
 
                 locks_delete_block(file_lock);
                 break;
         }
 
 out:
         locks_free_lock(file_lock);
         return error;
 }
 #endif /* BITS_PER_LONG == 32 */
 
 /*
  * This function is called when the file is being removed
  * from the task's fd array.  POSIX locks belonging to this task
  * are deleted at this time.
  */
 void locks_remove_posix(struct file *filp, fl_owner_t owner)
 {
         struct file_lock lock, **before;
 
         /*
          * If there are no locks held on this file, we don't need to call
          * posix_lock_file().  Another process could be setting a lock on this
          * file at the same time, but we wouldn't remove that lock anyway.
          */
         before = &filp->f_dentry->d_inode->i_flock;
         if (*before == NULL)
                 return;
 
         lock.fl_type = F_UNLCK;
         lock.fl_flags = FL_POSIX;
         lock.fl_start = 0;
         lock.fl_end = OFFSET_MAX;
         lock.fl_owner = owner;
         lock.fl_pid = current->tgid;
         lock.fl_file = filp;
         lock.fl_ops = NULL;
         lock.fl_lmops = NULL;
 
         if (filp->f_op && filp->f_op->lock != NULL) {
                 filp->f_op->lock(filp, F_SETLK, &lock);
                 goto out;
         }
 
         /* Can't use posix_lock_file here; we need to remove it no matter
          * which pid we have.
          */
         lock_kernel();
         while (*before != NULL) {
                 struct file_lock *fl = *before;
                 if (IS_POSIX(fl) && posix_same_owner(fl, &lock)) {
                         locks_delete_lock(before);
                         continue;
                 }
                 before = &fl->fl_next;
         }
         unlock_kernel();
 out:
         if (lock.fl_ops && lock.fl_ops->fl_release_private)
                 lock.fl_ops->fl_release_private(&lock);
 }
 
 EXPORT_SYMBOL(locks_remove_posix);
 
 /*
  * This function is called on the last close of an open file.
  */
 void locks_remove_flock(struct file *filp)
 {
         struct inode * inode = filp->f_dentry->d_inode; 
         struct file_lock *fl;
         struct file_lock **before;
 
         if (!inode->i_flock)
                 return;
 
         if (filp->f_op && filp->f_op->flock) {
                 struct file_lock fl = { .fl_flags = FL_FLOCK,
                                         .fl_type = F_UNLCK };
                 filp->f_op->flock(filp, F_SETLKW, &fl);
         }
 
         lock_kernel();
         before = &inode->i_flock;
 
         while ((fl = *before) != NULL) {
                 if (fl->fl_file == filp) {
                         /*
                          * We might have a POSIX lock that was created at the same time
                          * the filp was closed for the last time. Just remove that too,
                          * regardless of ownership, since nobody can own it.
                          */
                         if (IS_FLOCK(fl) || IS_POSIX(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_block_lock - blocks waiting for a file lock
  *      @blocker: the lock which is blocking
  *      @waiter: the lock which conflicts and has to wait
  *
  * lockd needs to block waiting for locks.
  */
 void
 posix_block_lock(struct file_lock *blocker, struct file_lock *waiter)
 {
         locks_insert_block(blocker, waiter);
 }
 
 EXPORT_SYMBOL(posix_block_lock);
 
 /**
  *      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.
  */
 void
 posix_unblock_lock(struct file *filp, struct file_lock *waiter)
 {
         /* 
          * A remote machine may cancel the lock request after it's been
          * granted locally.  If that happens, we need to delete the lock.
          */
         lock_kernel();
         if (waiter->fl_next) {
                 __locks_delete_block(waiter);
                 unlock_kernel();
         } else {
                 unlock_kernel();
                 waiter->fl_type = F_UNLCK;
                 posix_lock_file(filp, waiter);
         }
 }
 
 EXPORT_SYMBOL(posix_unblock_lock);
 
 static void lock_get_status(char* out, struct file_lock *fl, int id, char *pfx)
 {
         struct inode *inode = NULL;
 
         if (fl->fl_file != NULL)
                 inode = fl->fl_file->f_dentry->d_inode;
 
         out += sprintf(out, "%d:%s ", id, pfx);
         if (IS_POSIX(fl)) {
                 out += sprintf(out, "%6s %s ",
                              (fl->fl_flags & FL_ACCESS) ? "ACCESS" : "POSIX ",
                              (inode == NULL) ? "*NOINODE*" :
                              (IS_MANDLOCK(inode) &&
                               (inode->i_mode & (S_IXGRP | S_ISGID)) == S_ISGID) ?
                              "MANDATORY" : "ADVISORY ");
         } else if (IS_FLOCK(fl)) {
                 if (fl->fl_type & LOCK_MAND) {
                         out += sprintf(out, "FLOCK  MSNFS     ");
                 } else {
                         out += sprintf(out, "FLOCK  ADVISORY  ");
                 }
         } else if (IS_LEASE(fl)) {
                 out += sprintf(out, "LEASE  ");
                 if (fl->fl_type & F_INPROGRESS)
                         out += sprintf(out, "BREAKING  ");
                 else if (fl->fl_file)
                         out += sprintf(out, "ACTIVE    ");
                 else
                         out += sprintf(out, "BREAKER   ");
         } else {
                 out += sprintf(out, "UNKNOWN UNKNOWN  ");
         }
         if (fl->fl_type & LOCK_MAND) {
                 out += sprintf(out, "%s ",
                                (fl->fl_type & LOCK_READ)
                                ? (fl->fl_type & LOCK_WRITE) ? "RW   " : "READ "
                                : (fl->fl_type & LOCK_WRITE) ? "WRITE" : "NONE ");
         } else {
                 out += sprintf(out, "%s ",
                                (fl->fl_type & F_INPROGRESS)
                                ? (fl->fl_type & F_UNLCK) ? "UNLCK" : "READ "
                                : (fl->fl_type & F_WRLCK) ? "WRITE" : "READ ");
         }
         if (inode) {
 #ifdef WE_CAN_BREAK_LSLK_NOW
                 out += sprintf(out, "%d %s:%ld ", fl->fl_pid,
                                 inode->i_sb->s_id, inode->i_ino);
 #else
                 /* userspace relies on this representation of dev_t ;-( */
                 out += sprintf(out, "%d %02x:%02x:%ld ", fl->fl_pid,
                                 MAJOR(inode->i_sb->s_dev),
                                 MINOR(inode->i_sb->s_dev), inode->i_ino);
 #endif
         } else {
                 out += sprintf(out, "%d <none>:0 ", fl->fl_pid);
         }
         if (IS_POSIX(fl)) {
                 if (fl->fl_end == OFFSET_MAX)
                         out += sprintf(out, "%Ld EOF\n", fl->fl_start);
                 else
                         out += sprintf(out, "%Ld %Ld\n", fl->fl_start,
                                         fl->fl_end);
         } else {
                 out += sprintf(out, "0 EOF\n");
         }
 }
 
 static void move_lock_status(char **p, off_t* pos, off_t offset)
 {
         int len;
         len = strlen(*p);
         if(*pos >= offset) {
                 /* the complete line is valid */
                 *p += len;
                 *pos += len;
                 return;
         }
         if(*pos+len > offset) {
                 /* use the second part of the line */
                 int i = offset-*pos;
                 memmove(*p,*p+i,len-i);
                 *p += len-i;
                 *pos += len;
                 return;
         }
         /* discard the complete line */
         *pos += len;
 }
 
 /**
  *      get_locks_status        -       reports lock usage in /proc/locks
  *      @buffer: address in userspace to write into
  *      @start: ?
  *      @offset: how far we are through the buffer
  *      @length: how much to read
  */
 
 int get_locks_status(char *buffer, char **start, off_t offset, int length)
 {
         struct list_head *tmp;
         char *q = buffer;
         off_t pos = 0;
         int i = 0;
 
         lock_kernel();
         list_for_each(tmp, &file_lock_list) {
                 struct list_head *btmp;
                 struct file_lock *fl = list_entry(tmp, struct file_lock, fl_link);
                 lock_get_status(q, fl, ++i, "");
                 move_lock_status(&q, &pos, offset);
 
                 if(pos >= offset+length)
                         goto done;
 
                 list_for_each(btmp, &fl->fl_block) {
                         struct file_lock *bfl = list_entry(btmp,
                                         struct file_lock, fl_block);
                         lock_get_status(q, bfl, i, " ->");
                         move_lock_status(&q, &pos, offset);
 
                         if(pos >= offset+length)
                                 goto done;
                 }
         }
 done:
         unlock_kernel();
         *start = buffer;
         if(q-buffer < length)
                 return (q-buffer);
         return length;
 }
 
 /**
  *      lock_may_read - checks that the region is free of locks
  *      @inode: the inode that is being read
  *      @start: the first byte to read
  *      @len: the number of bytes to read
  *
  *      Emulates Windows locking requirements.  Whole-file
  *      mandatory locks (share modes) can prohibit a read and
  *      byte-range POSIX locks can prohibit a read if they overlap.
  *
  *      N.B. this function is only ever called
  *      from knfsd and ownership of locks is never checked.
  */
 int lock_may_read(struct inode *inode, loff_t start, unsigned long len)
 {
         struct file_lock *fl;
         int result = 1;
         lock_kernel();
         for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
                 if (IS_POSIX(fl)) {
                         if (fl->fl_type == F_RDLCK)
                                 continue;
                         if ((fl->fl_end < start) || (fl->fl_start > (start + len)))
                                 continue;
                 } else if (IS_FLOCK(fl)) {
                         if (!(fl->fl_type & LOCK_MAND))
                                 continue;
                         if (fl->fl_type & LOCK_READ)
                                 continue;
                 } else
                         continue;
                 result = 0;
                 break;
         }
         unlock_kernel();
         return result;
 }
 
 EXPORT_SYMBOL(lock_may_read);
 
 /**
  *      lock_may_write - checks that the region is free of locks
  *      @inode: the inode that is being written
  *      @start: the first byte to write
  *      @len: the number of bytes to write
  *
  *      Emulates Windows locking requirements.  Whole-file
  *      mandatory locks (share modes) can prohibit a write and
  *      byte-range POSIX locks can prohibit a write if they overlap.
  *
  *      N.B. this function is only ever called
  *      from knfsd and ownership of locks is never checked.
  */
 int lock_may_write(struct inode *inode, loff_t start, unsigned long len)
 {
         struct file_lock *fl;
         int result = 1;
         lock_kernel();
         for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
                 if (IS_POSIX(fl)) {
                         if ((fl->fl_end < start) || (fl->fl_start > (start + len)))
                                 continue;
                 } else if (IS_FLOCK(fl)) {
                         if (!(fl->fl_type & LOCK_MAND))
                                 continue;
                         if (fl->fl_type & LOCK_WRITE)
                                 continue;
                 } else
                         continue;
                 result = 0;
                 break;
         }
         unlock_kernel();
         return result;
 }
 
 EXPORT_SYMBOL(lock_may_write);
 
 static inline void __steal_locks(struct file *file, fl_owner_t from)
 {
         struct inode *inode = file->f_dentry->d_inode;
         struct file_lock *fl = inode->i_flock;
 
         while (fl) {
                 if (fl->fl_file == file && fl->fl_owner == from)
                         fl->fl_owner = current->files;
                 fl = fl->fl_next;
         }
 }
 
 /* When getting ready for executing a binary, we make sure that current
  * has a files_struct on its own. Before dropping the old files_struct,
  * we take over ownership of all locks for all file descriptors we own.
  * Note that we may accidentally steal a lock for a file that a sibling
  * has created since the unshare_files() call.
  */
 void steal_locks(fl_owner_t from)
 {
         struct files_struct *files = current->files;
         int i, j;
 
         if (from == files)
                 return;
 
         lock_kernel();
         j = 0;
         for (;;) {
                 unsigned long set;
                 i = j * __NFDBITS;
                 if (i >= files->max_fdset || i >= files->max_fds)
                         break;
                 set = files->open_fds->fds_bits[j++];
                 while (set) {
                         if (set & 1) {
                                 struct file *file = files->fd[i];
                                 if (file)
                                         __steal_locks(file, from);
                         }
                         i++;
                         set >>= 1;
                 }
         }
         unlock_kernel();
 }
 EXPORT_SYMBOL(steal_locks);
 
 static int __init filelock_init(void)
 {
         filelock_cache = kmem_cache_create("file_lock_cache",
                         sizeof(struct file_lock), 0, SLAB_PANIC,
                         init_once, NULL);
         return 0;
 }
 
 core_initcall(filelock_init);