ClabureDB: Classified Bug-Reports Database

   /*
    *  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/fdtable.h>
 #include <linux/fs.h>
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/security.h>
 #include <linux/slab.h>
 #include <linux/smp_lock.h>
 #include <linux/syscalls.h>
 #include <linux/time.h>
 #include <linux/rcupdate.h>
 #include <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)
 
 int leases_enable = 1;
 int lease_break_time = 45;
 
 #define for_each_lock(inode, lockp) \
         for (lockp = &inode->i_flock; *lockp != NULL; lockp = &(*lockp)->fl_next)
 
 static LIST_HEAD(file_lock_list);
 static LIST_HEAD(blocked_list);
 
 static struct kmem_cache *filelock_cache __read_mostly;
 
 /* Allocate an empty lock structure. */
 static struct file_lock *locks_alloc_lock(void)
 {
         return kmem_cache_alloc(filelock_cache, GFP_KERNEL);
 }
 
 static void locks_release_private(struct file_lock *fl)
 {
         if (fl->fl_ops) {
                 if (fl->fl_ops->fl_release_private)
                         fl->fl_ops->fl_release_private(fl);
                 fl->fl_ops = NULL;
         }
         if (fl->fl_lmops) {
                 if (fl->fl_lmops->fl_release_private)
                         fl->fl_lmops->fl_release_private(fl);
                 fl->fl_lmops = NULL;
         }
 
 }
 
 /* Free a lock which is not in use. */
 static void locks_free_lock(struct file_lock *fl)
 {
         BUG_ON(waitqueue_active(&fl->fl_wait));
         BUG_ON(!list_empty(&fl->fl_block));
         BUG_ON(!list_empty(&fl->fl_link));
 
         locks_release_private(fl);
         kmem_cache_free(filelock_cache, fl);
 }
 
 void locks_init_lock(struct file_lock *fl)
 {
         INIT_LIST_HEAD(&fl->fl_link);
         INIT_LIST_HEAD(&fl->fl_block);
         init_waitqueue_head(&fl->fl_wait);
         fl->fl_next = NULL;
         fl->fl_fasync = NULL;
         fl->fl_owner = NULL;
         fl->fl_pid = 0;
         fl->fl_nspid = NULL;
         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)
 {
         struct file_lock *lock = (struct file_lock *) foo;
 
         locks_init_lock(lock);
 }
 
 static void locks_copy_private(struct file_lock *new, struct file_lock *fl)
 {
         if (fl->fl_ops) {
                 if (fl->fl_ops->fl_copy_lock)
                         fl->fl_ops->fl_copy_lock(new, fl);
                 new->fl_ops = fl->fl_ops;
         }
         if (fl->fl_lmops) {
                 if (fl->fl_lmops->fl_copy_lock)
                         fl->fl_lmops->fl_copy_lock(new, fl);
                 new->fl_lmops = fl->fl_lmops;
         }
 }
 
 /*
  * Initialize a new lock from an existing file_lock structure.
  */
 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, int type)
 {
         switch (type) {
         case F_RDLCK:
         case F_WRLCK:
         case F_UNLCK:
                 fl->fl_type = type;
                 break;
         default:
                 return -EINVAL;
         }
         return 0;
 }
 
 /* Verify a "struct flock" and copy it to a "struct file_lock" as a POSIX
  * style lock.
  */
 static int flock_to_posix_lock(struct file *filp, struct file_lock *fl,
                                struct flock *l)
 {
         off_t start, end;
 
         switch (l->l_whence) {
         case SEEK_SET:
                 start = 0;
                 break;
         case SEEK_CUR:
                 start = filp->f_pos;
                 break;
         case SEEK_END:
                 start = i_size_read(filp->f_path.dentry->d_inode);
                 break;
         default:
                 return -EINVAL;
         }
 
         /* POSIX-1996 leaves the case l->l_len < 0 undefined;
            POSIX-2001 defines it. */
         start += l->l_start;
         if (start < 0)
                 return -EINVAL;
         fl->fl_end = OFFSET_MAX;
         if (l->l_len > 0) {
                 end = start + l->l_len - 1;
                 fl->fl_end = end;
         } else if (l->l_len < 0) {
                 end = start - 1;
                 fl->fl_end = end;
                 start += l->l_len;
                 if (start < 0)
                         return -EINVAL;
         }
         fl->fl_start = start;        /* we record the absolute position */
         if (fl->fl_end < fl->fl_start)
                 return -EOVERFLOW;
         
         fl->fl_owner = current->files;
         fl->fl_pid = current->tgid;
         fl->fl_file = filp;
         fl->fl_flags = FL_POSIX;
         fl->fl_ops = NULL;
         fl->fl_lmops = NULL;
 
         return assign_type(fl, l->l_type);
 }
 
 #if BITS_PER_LONG == 32
 static int flock64_to_posix_lock(struct file *filp, struct file_lock *fl,
                                  struct flock64 *l)
 {
         loff_t start;
 
         switch (l->l_whence) {
         case SEEK_SET:
                 start = 0;
                 break;
         case SEEK_CUR:
                 start = filp->f_pos;
                 break;
         case SEEK_END:
                 start = i_size_read(filp->f_path.dentry->d_inode);
                 break;
         default:
                 return -EINVAL;
         }
 
         start += l->l_start;
         if (start < 0)
                 return -EINVAL;
         fl->fl_end = OFFSET_MAX;
         if (l->l_len > 0) {
                 fl->fl_end = start + l->l_len - 1;
         } else if (l->l_len < 0) {
                 fl->fl_end = start - 1;
                 start += l->l_len;
                 if (start < 0)
                         return -EINVAL;
         }
         fl->fl_start = start;        /* we record the absolute position */
         if (fl->fl_end < fl->fl_start)
                 return -EOVERFLOW;
         
         fl->fl_owner = current->files;
         fl->fl_pid = current->tgid;
         fl->fl_file = filp;
         fl->fl_flags = FL_POSIX;
         fl->fl_ops = NULL;
         fl->fl_lmops = NULL;
 
         switch (l->l_type) {
         case F_RDLCK:
         case F_WRLCK:
         case F_UNLCK:
                 fl->fl_type = l->l_type;
                 break;
         default:
                 return -EINVAL;
         }
 
         return (0);
 }
 #endif
 
 /* default lease lock manager operations */
 static void lease_break_callback(struct file_lock *fl)
 {
         kill_fasync(&fl->fl_fasync, SIGIO, POLL_MSG);
 }
 
 static void lease_release_private_callback(struct file_lock *fl)
 {
         if (!fl->fl_file)
                 return;
 
         f_delown(fl->fl_file);
         fl->fl_file->f_owner.signum = 0;
 }
 
 static int lease_mylease_callback(struct file_lock *fl, struct file_lock *try)
 {
         return fl->fl_file == try->fl_file;
 }
 
 static struct lock_manager_operations lease_manager_ops = {
         .fl_break = lease_break_callback,
         .fl_release_private = lease_release_private_callback,
         .fl_mylease = lease_mylease_callback,
         .fl_change = lease_modify,
 };
 
 /*
  * Initialize a lease, use the default lock manager operations
  */
 static int lease_init(struct file *filp, int type, struct file_lock *fl)
  {
         if (assign_type(fl, type) != 0)
                 return -EINVAL;
 
         fl->fl_owner = current->files;
         fl->fl_pid = current->tgid;
 
         fl->fl_file = filp;
         fl->fl_flags = FL_LEASE;
         fl->fl_start = 0;
         fl->fl_end = OFFSET_MAX;
         fl->fl_ops = NULL;
         fl->fl_lmops = &lease_manager_ops;
         return 0;
 }
 
 /* Allocate a file_lock initialised to this type of lease */
 static struct file_lock *lease_alloc(struct file *filp, int type)
 {
         struct file_lock *fl = locks_alloc_lock();
         int error = -ENOMEM;
 
         if (fl == NULL)
                 return ERR_PTR(error);
 
         error = lease_init(filp, type, fl);
         if (error) {
                 locks_free_lock(fl);
                 return ERR_PTR(error);
         }
         return fl;
 }
 
 /* Check if two locks overlap each other.
  */
 static inline int locks_overlap(struct file_lock *fl1, struct file_lock *fl2)
 {
         return ((fl1->fl_end >= fl2->fl_start) &&
                 (fl2->fl_end >= fl1->fl_start));
 }
 
 /*
  * Check whether two locks have the same owner.
  */
 static int posix_same_owner(struct file_lock *fl1, struct file_lock *fl2)
 {
         if (fl1->fl_lmops && fl1->fl_lmops->fl_compare_owner)
                 return fl2->fl_lmops == fl1->fl_lmops &&
                         fl1->fl_lmops->fl_compare_owner(fl1, fl2);
         return fl1->fl_owner == fl2->fl_owner;
 }
 
 /* Remove waiter from blocker's block list.
  * When blocker ends up pointing to itself then the list is empty.
  */
 static void __locks_delete_block(struct file_lock *waiter)
 {
         list_del_init(&waiter->fl_block);
         list_del_init(&waiter->fl_link);
         waiter->fl_next = NULL;
 }
 
 /*
  */
 static void locks_delete_block(struct file_lock *waiter)
 {
         lock_kernel();
         __locks_delete_block(waiter);
         unlock_kernel();
 }
 
 /* Insert waiter into blocker's block list.
  * We use a circular list so that processes can be easily woken up in
  * the order they blocked. The documentation doesn't require this but
  * it seems like the reasonable thing to do.
  */
 static void locks_insert_block(struct file_lock *blocker, 
                                struct file_lock *waiter)
 {
         BUG_ON(!list_empty(&waiter->fl_block));
         list_add_tail(&waiter->fl_block, &blocker->fl_block);
         waiter->fl_next = blocker;
         if (IS_POSIX(blocker))
                 list_add(&waiter->fl_link, &blocked_list);
 }
 
 /* Wake up processes blocked waiting for blocker.
  * If told to wait then schedule the processes until the block list
  * is empty, otherwise empty the block list ourselves.
  */
 static void locks_wake_up_blocks(struct file_lock *blocker)
 {
         while (!list_empty(&blocker->fl_block)) {
                 struct file_lock *waiter;
 
                 waiter = list_first_entry(&blocker->fl_block,
                                 struct file_lock, fl_block);
                 __locks_delete_block(waiter);
                 if (waiter->fl_lmops && waiter->fl_lmops->fl_notify)
                         waiter->fl_lmops->fl_notify(waiter);
                 else
                         wake_up(&waiter->fl_wait);
         }
 }
 
 /* Insert file lock fl into an inode's lock list at the position indicated
  * by pos. At the same time add the lock to the global file lock list.
  */
 static void locks_insert_lock(struct file_lock **pos, struct file_lock *fl)
 {
         list_add(&fl->fl_link, &file_lock_list);
 
         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);
 
         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_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_kernel();
         for (cfl = filp->f_path.dentry->d_inode->i_flock; cfl; cfl = cfl->fl_next) {
                 if (!IS_POSIX(cfl))
                         continue;
                 if (posix_locks_conflict(fl, cfl))
                         break;
         }
         if (cfl) {
                 __locks_copy_lock(fl, cfl);
                 if (cfl->fl_nspid)
                         fl->fl_pid = pid_vnr(cfl->fl_nspid);
         } else
                 fl->fl_type = F_UNLCK;
         unlock_kernel();
         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;
 
         lock_kernel();
         if (request->fl_flags & FL_ACCESS)
                 goto find_conflict;
 
         if (request->fl_type != F_UNLCK) {
                 error = -ENOMEM;
                 new_fl = locks_alloc_lock();
                 if (new_fl == NULL)
                         goto out;
                 error = 0;
         }
 
         for_each_lock(inode, before) {
                 struct file_lock *fl = *before;
                 if (IS_POSIX(fl))
                         break;
                 if (IS_LEASE(fl))
                         continue;
                 if (filp != fl->fl_file)
                         continue;
                 if (request->fl_type == fl->fl_type)
                         goto out;
                 found = 1;
                 locks_delete_lock(before);
                 break;
         }
 
         if (request->fl_type == F_UNLCK) {
                 if ((request->fl_flags & FL_EXISTS) && !found)
                         error = -ENOENT;
                 goto out;
         }
 
         /*
          * If a higher-priority process was blocked on the old file lock,
          * give it the opportunity to lock the file.
          */
         if (found)
                 cond_resched_bkl();
 
 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_kernel();
         if (new_fl)
                 locks_free_lock(new_fl);
         return error;
 }
 
 static int __posix_lock_file(struct inode *inode, struct file_lock *request, struct file_lock *conflock)
 {
         struct file_lock *fl;
         struct file_lock *new_fl = NULL;
         struct file_lock *new_fl2 = NULL;
         struct file_lock *left = NULL;
         struct file_lock *right = NULL;
         struct file_lock **before;
         int error, added = 0;
 
         /*
          * We may need two file_lock structures for this operation,
          * so we get them in advance to avoid races.
          *
          * In some cases we can be sure, that no new locks will be needed
          */
         if (!(request->fl_flags & FL_ACCESS) &&
             (request->fl_type != F_UNLCK ||
              request->fl_start != 0 || request->fl_end != OFFSET_MAX)) {
                 new_fl = locks_alloc_lock();
                 new_fl2 = locks_alloc_lock();
         }
 
         lock_kernel();
         if (request->fl_type != F_UNLCK) {
                 for_each_lock(inode, before) {
                         fl = *before;
                         if (!IS_POSIX(fl))
                                 continue;
                         if (!posix_locks_conflict(request, fl))
                                 continue;
                         if (conflock)
                                 __locks_copy_lock(conflock, fl);
                         error = -EAGAIN;
                         if (!(request->fl_flags & FL_SLEEP))
                                 goto out;
                         error = -EDEADLK;
                         if (posix_locks_deadlock(request, fl))
                                 goto out;
                         error = 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_kernel();
         /*
          * Free any unused locks.
          */
         if (new_fl)
                 locks_free_lock(new_fl);
         if (new_fl2)
                locks_free_lock(new_fl2);
        return error;
}

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

/**
 * posix_lock_file_wait - Apply a POSIX-style lock to a file
 * @filp: The file to apply the lock to
 * @fl: The lock to be applied
 *
 * Add a POSIX style lock to a file.
 * We merge adjacent & overlapping locks whenever possible.
 * POSIX locks are sorted by owner task, then by starting address
 */
int posix_lock_file_wait(struct file *filp, struct file_lock *fl)
{
        int error;
        might_sleep ();
        for (;;) {
                error = posix_lock_file(filp, fl, NULL);
                if (error != 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_kernel();
        for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
                if (!IS_POSIX(fl))
                        continue;
                if (fl->fl_owner != owner)
                        break;
        }
        unlock_kernel();
        return fl ? -EAGAIN : 0;
}

/**
 * locks_mandatory_area - Check for a conflicting lock
 * @read_write: %FLOCK_VERIFY_WRITE for exclusive access, %FLOCK_VERIFY_READ
 *                for shared
 * @inode:      the file to check
 * @filp:       how the file was opened (if it was)
 * @offset:     start of area to check
 * @count:      length of area to check
 *
 * Searches the inode's list of locks to find any POSIX locks which conflict.
 * This function is called from rw_verify_area() and
 * locks_verify_truncate().
 */
int locks_mandatory_area(int read_write, struct inode *inode,
                         struct file *filp, loff_t offset,
                         size_t count)
{
        struct file_lock fl;
        int error;

        locks_init_lock(&fl);
        fl.fl_owner = current->files;
        fl.fl_pid = current->tgid;
        fl.fl_file = filp;
        fl.fl_flags = FL_POSIX | FL_ACCESS;
        if (filp && !(filp->f_flags & O_NONBLOCK))
                fl.fl_flags |= FL_SLEEP;
        fl.fl_type = (read_write == FLOCK_VERIFY_WRITE) ? F_WRLCK : F_RDLCK;
        fl.fl_start = offset;
        fl.fl_end = offset + count - 1;

        for (;;) {
                error = __posix_lock_file(inode, &fl, NULL);
                if (error != 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);

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

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

EXPORT_SYMBOL(lease_modify);

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

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

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

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

        lock_kernel();

        time_out_leases(inode);

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

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

        if (mode & FMODE_WRITE) {
                /* If we want write access, we have to revoke any lease. */
                future = F_UNLCK | F_INPROGRESS;
        } else if (flock->fl_type & F_INPROGRESS) {
                /* If the lease is already being broken, we just leave it */
                future = flock->fl_type;
        } else if (flock->fl_type & F_WRLCK) {
                /* Downgrade the exclusive lease to a read-only lease. */
                future = F_RDLCK | F_INPROGRESS;
        } else {
                /* the existing lease was read-only, so we can read too. */
                goto out;
        }

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

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

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

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

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

out:
        unlock_kernel();
        if (!IS_ERR(new_fl))
                locks_free_lock(new_fl);
        return error;
}

EXPORT_SYMBOL(__break_lease);

/**
 *        lease_get_mtime - 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_kernel();
        time_out_leases(filp->f_path.dentry->d_inode);
        for (fl = filp->f_path.dentry->d_inode->i_flock; fl && IS_LEASE(fl);
                        fl = fl->fl_next) {
                if (fl->fl_file == filp) {
                        type = fl->fl_type & ~F_INPROGRESS;
                        break;
                }
        }
        unlock_kernel();
        return type;
}

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

        if ((current->fsuid != inode->i_uid) && !capable(CAP_LEASE))
                return -EACCES;
        if (!S_ISREG(inode->i_mode))
                return -EINVAL;
        error = security_file_lock(filp, arg);
        if (error)
                return error;

        time_out_leases(inode);

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

        lease = *flp;

        if (arg != F_UNLCK) {
                error = -ENOMEM;
                new_fl = locks_alloc_lock();
                if (new_fl == NULL)
                        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 (lease->fl_lmops->fl_mylease(fl, lease))
                        my_before = before;
                else if (fl->fl_type == (F_INPROGRESS | F_UNLCK))
                        /*
                         * Someone is in the process of opening this
                         * file for writing so we may not take an
                         * exclusive lease on it.
                         */
                        wrlease_count++;
                else
                        rdlease_count++;
        }

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

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

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

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

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

        *flp = new_fl;
        return 0;

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

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

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

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

        return error;
}
EXPORT_SYMBOL_GPL(vfs_setlease);

/**
 *        fcntl_setlease        -        sets a lease on an open file
 *        @fd: open file descriptor
 *        @filp: file pointer
 *        @arg: type of lease to obtain
 *
 *        Call this fcntl to establish a lease on the file.
 *        Note that you also need to call %F_SETSIG to
 *        receive a signal when the lease is broken.
 */
int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
{
        struct file_lock fl, *flp = &fl;
        struct inode *inode = filp->f_path.dentry->d_inode;
        int error;

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

        lock_kernel();

        error = vfs_setlease(filp, arg, &flp);
        if (error || arg == F_UNLCK)
                goto out_unlock;

        error = fasync_helper(fd, filp, 1, &flp->fl_fasync);
        if (error < 0) {
                /* remove lease just inserted by setlease */
                flp->fl_type = F_UNLCK | F_INPROGRESS;
                flp->fl_break_time = jiffies - 10;
                time_out_leases(inode);
                goto out_unlock;
        }

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

/**
 * flock_lock_file_wait - Apply a FLOCK-style lock to a file
 * @filp: The file to apply the lock to
 * @fl: The lock to be applied
 *
 * Add a FLOCK style lock to a file.
 */
int flock_lock_file_wait(struct file *filp, struct file_lock *fl)
{
        int error;
        might_sleep();
        for (;;) {
                error = flock_lock_file(filp, fl);
                if (error != 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.
 */
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 & (FMODE_READ|FMODE_WRITE)))
                goto out_putf;

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

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

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

 out_free:
        locks_free_lock(lock);

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

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

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

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

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

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

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

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

/**
 * vfs_lock_file - file byte range lock
 * @filp: The file to apply the lock to
 * @cmd: type of locking operation (F_SETLK, F_GETLK, etc.)
 * @fl: The lock to be applied
 * @conf: Place to return a copy of the conflicting lock, if found.
 *
 * A caller that doesn't care about the conflicting lock may pass NULL
 * as the final argument.
 *
 * If the filesystem defines a private ->lock() method, then @conf will
 * be left unchanged; so a caller that cares should initialize it to
 * some acceptable default.
 *
 * To avoid blocking kernel daemons, such as lockd, that need to acquire POSIX
 * locks, the ->lock() interface may return asynchronously, before the lock has
 * been granted or denied by the underlying filesystem, if (and only if)
 * fl_grant is set. Callers expecting ->lock() to return asynchronously
 * will only use F_SETLK, not F_SETLKW; they will set FL_SLEEP if (and only if)
 * the request is for a blocking lock. When ->lock() does return asynchronously,
 * it must return FILE_LOCK_DEFERRED, and call ->fl_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
 * ->fl_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_kernel();
        before = &inode->i_flock;

        while ((fl = *before) != NULL) {
                if (fl->fl_file == filp) {
                        if (IS_FLOCK(fl)) {
                                locks_delete_lock(before);
                                continue;
                        }
                        if (IS_LEASE(fl)) {
                                lease_modify(before, F_UNLCK);
                                continue;
                        }
                        /* What? */
                        BUG();
                 }
                before = &fl->fl_next;
        }
        unlock_kernel();
}

/**
 *        posix_unblock_lock - stop waiting for a file lock
 *      @filp:   how the file was opened
 *        @waiter: the lock which was waiting
 *
 *        lockd needs to block waiting for locks.
 */
int
posix_unblock_lock(struct file *filp, struct file_lock *waiter)
{
        int status = 0;

        lock_kernel();
        if (waiter->fl_next)
                __locks_delete_block(waiter);
        else
                status = -ENOENT;
        unlock_kernel();
        return status;
}

EXPORT_SYMBOL(posix_unblock_lock);

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

EXPORT_SYMBOL_GPL(vfs_cancel_lock);

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

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

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

        f->private++;
        return 0;
}

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

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

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

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(filp, &locks_seq_operations);
}

static const struct file_operations proc_locks_operations = {
        .open                = locks_open,
        .read                = seq_read,
        .llseek                = seq_lseek,
        .release        = seq_release,
};

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_kernel();
        for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
                if (IS_POSIX(fl)) {
                        if (fl->fl_type == F_RDLCK)
                                continue;
                        if ((fl->fl_end < start) || (fl->fl_start > (start + len)))
                                continue;
                } else if (IS_FLOCK(fl)) {
                        if (!(fl->fl_type & LOCK_MAND))
                                continue;
                        if (fl->fl_type & LOCK_READ)
                                continue;
                } else
                        continue;
                result = 0;
                break;
        }
        unlock_kernel();
        return result;
}

EXPORT_SYMBOL(lock_may_read);

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

EXPORT_SYMBOL(lock_may_write);

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

core_initcall(filelock_init);