newlib-cygwin/winsup/cygwin/flock.cc

/* flock.cc.  NT specific implementation of advisory file locking.

   Copyright 2003, 2008, 2009 Red Hat, Inc.

   This file is part of Cygwin.

   This software is a copyrighted work licensed under the terms of the
   Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
   details. */

/* The basic mechanism as well as the datastructures used in the below
   implementation are taken from the FreeBSD repository on 2008-03-18.
   The essential code of the lf_XXX functions has been taken from the
   module src/sys/kern/kern_lockf.c.  It has been adapted to use NT
   global namespace subdirs and event objects for synchronization
   purposes.

   So, the following copyright applies to most of the code in the lf_XXX
   functions.

 * Copyright (c) 1982, 1986, 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Scooter Morris at Genentech Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)ufs_lockf.c 8.3 (Berkeley) 1/6/94
*/

/*
 * The flock() function is based upon source taken from the Red Hat
 * implementation used in their imap-2002d SRPM.
 *
 * $RH: flock.c,v 1.2 2000/08/23 17:07:00 nalin Exp $
 */

/* The lockf function is based upon FreeBSD sources with the following
 * copyright.
 */
/*
 * Copyright (c) 1997 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Klaus Klein.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include "winsup.h"
#include <assert.h>
#include <sys/file.h>
#include <unistd.h>
#include <stdlib.h>
#include "cygerrno.h"
#include "security.h"
#include "shared_info.h"
#include "path.h"
#include "fhandler.h"
#include "dtable.h"
#include "cygheap.h"
#include "pinfo.h"
#include "sigproc.h"
#include "cygtls.h"
#include "tls_pbuf.h"
#include "ntdll.h"
#include <sys/queue.h>
#include <wchar.h>

#define F_WAIT 0x10	/* Wait until lock is granted */
#define F_FLOCK 0x20	/* Use flock(2) semantics for lock */
#define F_POSIX	0x40	/* Use POSIX semantics for lock */

#ifndef OFF_MAX
#define OFF_MAX LLONG_MAX
#endif

static NO_COPY muto lockf_guard;

#define INODE_LIST_LOCK()	(lockf_guard.init ("lockf_guard")->acquire ())
#define INODE_LIST_UNLOCK()	(lockf_guard.release ())

#define LOCK_OBJ_NAME_LEN	64

#define FLOCK_INODE_DIR_ACCESS	(DIRECTORY_QUERY \
				 | DIRECTORY_TRAVERSE \
				 | DIRECTORY_CREATE_OBJECT \
				 | READ_CONTROL)

#define FLOCK_EVENT_ACCESS	(EVENT_QUERY_STATE \
				 | SYNCHRONIZE \
				 | READ_CONTROL)

/* This function takes the own process security descriptor DACL and adds
   SYNCHRONIZE permissions for everyone.  This allows all processes
   to wait for this process to die when blocking in a F_SETLKW on a lock
   which is hold by this process. */
static void
allow_others_to_sync ()
{
  static NO_COPY bool done;

  if (done)
    return;

  NTSTATUS status;
  PACL dacl;
  LPVOID ace;
  ULONG len;

  /* Get this process DACL.  We use a temporary path buffer in TLS space
     to avoid having to alloc 64K from the stack. */
  tmp_pathbuf tp;
  PSECURITY_DESCRIPTOR sd = (PSECURITY_DESCRIPTOR) tp.w_get ();
  status = NtQuerySecurityObject (hMainProc, DACL_SECURITY_INFORMATION, sd,
				  NT_MAX_PATH * sizeof (WCHAR), &len);
  if (!NT_SUCCESS (status))
    {
      debug_printf ("NtQuerySecurityObject: %p", status);
      return;
    }
  /* Create a valid dacl pointer and set it's size to be as big as
     there's room in the temporary buffer.  Note that the descriptor
     is in self-relative format. */
  dacl = (PACL) ((char *) sd + (uintptr_t) sd->Dacl);
  dacl->AclSize = NT_MAX_PATH * sizeof (WCHAR) - ((char *) dacl - (char *) sd);
  /* Allow everyone to SYNCHRONIZE with this process. */
  if (!AddAccessAllowedAce (dacl, ACL_REVISION, SYNCHRONIZE,
			    well_known_world_sid))
    {
      debug_printf ("AddAccessAllowedAce: %lu", GetLastError ());
      return;
    }
  /* Set the size of the DACL correctly. */
  if (!FindFirstFreeAce (dacl, &ace))
    {
      debug_printf ("FindFirstFreeAce: %lu", GetLastError ());
      return;
    }
  dacl->AclSize = (char *) ace - (char *) dacl;
  /* Write the DACL back. */
  status = NtSetSecurityObject (hMainProc, DACL_SECURITY_INFORMATION, sd);
  if (!NT_SUCCESS (status))
    {
      debug_printf ("NtSetSecurityObject: %p", status);
      return;
    }
  done = true;
}

/* Get the handle count of an object. */
static ULONG
get_obj_handle_count (HANDLE h)
{
  OBJECT_BASIC_INFORMATION obi;
  NTSTATUS status;
  ULONG hdl_cnt = 0;

  status = NtQueryObject (h, ObjectBasicInformation, &obi, sizeof obi, NULL);
  if (!NT_SUCCESS (status))
    debug_printf ("NtQueryObject: %p\n", status);
  else
    hdl_cnt = obi.HandleCount;
  return hdl_cnt;
}

/* Per lock class. */
class lockf_t
{
  public:
    short           lf_flags; /* Semantics: F_POSIX, F_FLOCK, F_WAIT */
    short           lf_type;  /* Lock type: F_RDLCK, F_WRLCK */
    _off64_t        lf_start; /* Byte # of the start of the lock */
    _off64_t        lf_end;   /* Byte # of the end of the lock (-1=EOF) */
    long long       lf_id;    /* Cygwin PID for POSIX locks, a unique id per
				 file table entry for BSD flock locks. */
    DWORD           lf_wid;   /* Win PID of the resource holding the lock */
    class lockf_t **lf_head;  /* Back pointer to the head of the lockf_t list */
    class inode_t  *lf_inode; /* Back pointer to the inode_t */
    class lockf_t  *lf_next;  /* Pointer to the next lock on this inode_t */
    HANDLE          lf_obj;   /* Handle to the lock event object. */

    lockf_t ()
    : lf_flags (0), lf_type (0), lf_start (0), lf_end (0), lf_id (0),
      lf_wid (0), lf_head (NULL), lf_inode (NULL),
      lf_next (NULL), lf_obj (NULL)
    {}
    lockf_t (class inode_t *node, class lockf_t **head, short flags, short type,
	   _off64_t start, _off64_t end, long long id, DWORD wid)
    : lf_flags (flags), lf_type (type), lf_start (start), lf_end (end),
      lf_id (id), lf_wid (wid), lf_head (head), lf_inode (node),
      lf_next (NULL), lf_obj (NULL)
    {}
    ~lockf_t ();

    /* Used to create all locks list in a given TLS buffer. */
    void *operator new (size_t size, void *p)
    { return p; }
    /* Used to store own lock list in the cygheap. */
    void *operator new (size_t size)
    { return cmalloc (HEAP_FHANDLER, sizeof (lockf_t)); }
    /* Never call on node->i_all_lf! */
    void operator delete (void *p)
    { cfree (p); }

    void create_lock_obj ();
    bool open_lock_obj ();
    void del_lock_obj (HANDLE fhdl, bool signal = false);
};

/* Per inode_t class */
class inode_t
{
  friend class lockf_t;

  public:
    LIST_ENTRY (inode_t)  i_next;
    lockf_t              *i_lockf;  /* List of locks of this process. */
    lockf_t              *i_all_lf; /* Temp list of all locks for this file. */

    __dev32_t             i_dev;    /* Device ID */
    __ino64_t             i_ino;    /* inode number */

  private:
    HANDLE                i_dir;
    HANDLE                i_mtx;
    unsigned long	  i_wait;   /* Number of blocked threads waiting for
				       a blocking lock. */

  public:
    inode_t (__dev32_t dev, __ino64_t ino);
    ~inode_t ();

    void *operator new (size_t size)
    { return cmalloc (HEAP_FHANDLER, sizeof (inode_t)); }
    void operator delete (void *p)
    { cfree (p); }

    static inode_t *get (__dev32_t dev, __ino64_t ino, bool create_if_missing);

    void LOCK () { WaitForSingleObject (i_mtx, INFINITE); }
    void UNLOCK () { ReleaseMutex (i_mtx); }

    void wait () { ++i_wait; }
    void unwait () { if (i_wait > 0) --i_wait; }
    bool waiting () { return i_wait > 0; } 

    lockf_t *get_all_locks_list ();

    bool del_my_locks (long long id, HANDLE fhdl);
};

inode_t::~inode_t ()
{
  lockf_t *lock, *n_lock;
  for (lock = i_lockf; lock && (n_lock = lock->lf_next, 1); lock = n_lock)
    delete lock;
  NtClose (i_mtx);
  NtClose (i_dir);
}

bool
inode_t::del_my_locks (long long id, HANDLE fhdl)
{
  lockf_t *lock, *n_lock;
  lockf_t **prev = &i_lockf;
  int lc = 0;
  for (lock = *prev; lock && (n_lock = lock->lf_next, 1); lock = n_lock)
    {
      if (lock->lf_flags & F_POSIX)
	{
	  /* Delete all POSIX locks. */
	  *prev = n_lock;
	  ++lc;
	  delete lock;
	}
      else if (id && lock->lf_id == id)
	{
	  int cnt = 0;
	  cygheap_fdenum cfd (true);
	  while (cfd.next () >= 0)
	    if (cfd->get_unique_id () == lock->lf_id && ++cnt > 1)
	      break;
	  /* Delete BSD flock lock when no other fd in this process references
	     it anymore. */
	  if (cnt <= 1)
	    {
	      *prev = n_lock;
	      lock->del_lock_obj (fhdl);
	      delete lock;
	    }
	}
      else
	prev = &lock->lf_next;
    }
  return i_lockf == NULL;
}

/* Used to delete the locks on a file hold by this process.  Called from
   close(2) and fixup_after_fork, as well as from fixup_after_exec in
   case the close_on_exec flag is set.  The whole inode is deleted as
   soon as no lock exists on it anymore. */
void
fhandler_base::del_my_locks (bool after_fork)
{
  INODE_LIST_LOCK ();
  inode_t *node = inode_t::get (get_dev (), get_ino (), false);
  if (node)
    {
      bool no_locks_left =
	node->del_my_locks (after_fork ? 0 : get_unique_id (), get_handle ());
      if (no_locks_left)
	{
	  LIST_REMOVE (node, i_next);
	  node->UNLOCK ();
	  delete node;
	}
      else
	node->UNLOCK ();
    }
  INODE_LIST_UNLOCK ();
}

/* Called in an execed child.  The exec'ed process must allow SYNCHRONIZE
   access to everyone if at least one inode exists.
   The lock owner's Windows PID changed and all POSIX lock event objects
   have to be relabeled so that waiting processes know which process to
   wait on.  If the node has been abandoned due to close_on_exec on the
   referencing fhandlers, remove the inode entirely. */
void
fixup_lockf_after_exec ()
{
  inode_t *node, *next_node;

  INODE_LIST_LOCK ();
  if (LIST_FIRST (&cygheap->inode_list))
    allow_others_to_sync ();
  LIST_FOREACH_SAFE (node, &cygheap->inode_list, i_next, next_node)
    {
      int cnt = 0;
      cygheap_fdenum cfd (true);
      while (cfd.next () >= 0)
	if (cfd->get_dev () == node->i_dev
	    && cfd->get_ino () == node->i_ino
	    && ++cnt > 1)
	  break;
      if (cnt == 0)
	{
	  LIST_REMOVE (node, i_next);
	  delete node;
	}
      else
	{
	  node->LOCK ();
	  for (lockf_t *lock = node->i_lockf; lock; lock = lock->lf_next)
	    if (lock->lf_flags & F_POSIX)
	      {
		lock->del_lock_obj (NULL);
		lock->lf_wid = myself->dwProcessId;
		lock->create_lock_obj ();
	      }
	  node->UNLOCK ();
	}
    }
  INODE_LIST_UNLOCK ();
}

/* static method to return a pointer to the inode_t structure for a specific
   file.  The file is specified by the device and inode_t number.  If inode_t
   doesn't exist, create it. */
inode_t *
inode_t::get (__dev32_t dev, __ino64_t ino, bool create_if_missing)
{
  inode_t *node;

  INODE_LIST_LOCK ();
  LIST_FOREACH (node, &cygheap->inode_list, i_next)
    if (node->i_dev == dev && node->i_ino == ino)
      break;
  if (!node && create_if_missing)
    {
      node = new inode_t (dev, ino);
      if (node)
	LIST_INSERT_HEAD (&cygheap->inode_list, node, i_next);
    }
  if (node)
    node->LOCK ();
  INODE_LIST_UNLOCK ();
  return node;
}

inode_t::inode_t (__dev32_t dev, __ino64_t ino)
: i_lockf (NULL), i_all_lf (NULL), i_dev (dev), i_ino (ino), i_wait (0L)
{
  HANDLE parent_dir;
  WCHAR name[48];
  UNICODE_STRING uname;
  OBJECT_ATTRIBUTES attr;
  NTSTATUS status;

  parent_dir = get_shared_parent_dir ();
  /* Create a subdir which is named after the device and inode_t numbers
     of the given file, in hex notation. */
  int len = __small_swprintf (name, L"flock-%08x-%016X", dev, ino);
  RtlInitCountedUnicodeString (&uname, name, len * sizeof (WCHAR));
  InitializeObjectAttributes (&attr, &uname, OBJ_INHERIT | OBJ_OPENIF,
			      parent_dir, everyone_sd (FLOCK_INODE_DIR_ACCESS));
  status = NtCreateDirectoryObject (&i_dir, FLOCK_INODE_DIR_ACCESS, &attr);
  if (!NT_SUCCESS (status))
    api_fatal ("NtCreateDirectoryObject(inode): %p", status);
  /* Create a mutex object in the file specific dir, which is used for
     access synchronization on the dir and its objects. */
  RtlInitUnicodeString (&uname, L"mtx");
  InitializeObjectAttributes (&attr, &uname, OBJ_INHERIT | OBJ_OPENIF, i_dir,
			      everyone_sd (CYG_MUTANT_ACCESS));
  status = NtCreateMutant (&i_mtx, CYG_MUTANT_ACCESS, &attr, FALSE);
  if (!NT_SUCCESS (status))
    api_fatal ("NtCreateMutant(inode): %p", status);
}

/* Enumerate all lock event objects for this file and create a lockf_t
   list in the i_all_lf member.  This list is searched in lf_getblock
   for locks which potentially block our lock request. */

/* Number of lockf_t structs which fit in the temporary buffer. */
#define MAX_LOCKF_CNT	((intptr_t)((NT_MAX_PATH * sizeof (WCHAR)) \
				    / sizeof (lockf_t)))

lockf_t *
inode_t::get_all_locks_list ()
{
  struct fdbi
  {
    DIRECTORY_BASIC_INFORMATION dbi;
    WCHAR buf[2][NAME_MAX + 1];
  } f;
  ULONG context;
  NTSTATUS status;
  lockf_t *lock = i_all_lf;

  for (BOOLEAN restart = TRUE;
       NT_SUCCESS (status = NtQueryDirectoryObject (i_dir, &f, sizeof f, TRUE,
						    restart, &context, NULL));
       restart = FALSE)
    {
      if (f.dbi.ObjectName.Length != LOCK_OBJ_NAME_LEN * sizeof (WCHAR))
	continue;
      wchar_t *wc = f.dbi.ObjectName.Buffer, *endptr;
      /* "%02x-%01x-%016X-%016X-%016X-%08x",
	 lf_flags, lf_type, lf_start, lf_end, lf_id, lf_wid */
      wc[LOCK_OBJ_NAME_LEN] = L'\0';
      short flags = wcstol (wc, &endptr, 16);
      if ((flags & ~(F_FLOCK | F_POSIX)) != 0
	  || ((flags & (F_FLOCK | F_POSIX)) == (F_FLOCK | F_POSIX)))
	continue;
      short type = wcstol (endptr + 1, &endptr, 16);
      if ((type != F_RDLCK && type != F_WRLCK) || !endptr || *endptr != L'-')
	continue;
      _off64_t start = (_off64_t) wcstoull (endptr + 1, &endptr, 16);
      if (start < 0 || !endptr || *endptr != L'-')
	continue;
      _off64_t end = (_off64_t) wcstoull (endptr + 1, &endptr, 16);
      if (end < -1LL || (end > 0 && end < start) || !endptr || *endptr != L'-')
	continue;
      long long id = wcstoll (endptr + 1, &endptr, 16);
      if (!endptr || *endptr != L'-'
	  || ((flags & F_POSIX) && (id < 1 || id > ULONG_MAX)))
	continue;
      DWORD wid = wcstoul (endptr + 1, &endptr, 16);
      if (endptr && *endptr != L'\0')
	continue;
      if (lock - i_all_lf >= MAX_LOCKF_CNT)
	{
	  system_printf ("Warning, can't handle more than %d locks per file.",
			 MAX_LOCKF_CNT);
	  break;
	}
      if (lock > i_all_lf)
	lock[-1].lf_next = lock;
      new (lock++) lockf_t (this, &i_all_lf, flags, type, start, end, id, wid);
    }
  /* If no lock has been found, return NULL. */
  if (lock == i_all_lf)
    return NULL;
  return i_all_lf;
}

/* Create the lock event object in the file's subdir in the NT global
   namespace.  The name is constructed from the lock properties which
   identify it uniquely, all values in hex.  See the __small_swprintf
   call right at the start.  */
void
lockf_t::create_lock_obj ()
{
  WCHAR name[LOCK_OBJ_NAME_LEN + 1];
  UNICODE_STRING uname;
  OBJECT_ATTRIBUTES attr;
  NTSTATUS status;

  __small_swprintf (name, L"%02x-%01x-%016X-%016X-%016X-%08x",
			  lf_flags & (F_POSIX | F_FLOCK), lf_type, lf_start,
			  lf_end, lf_id, lf_wid);
  RtlInitCountedUnicodeString (&uname, name,
			       LOCK_OBJ_NAME_LEN * sizeof (WCHAR));
  InitializeObjectAttributes (&attr, &uname, OBJ_INHERIT, lf_inode->i_dir,
			      everyone_sd (FLOCK_EVENT_ACCESS));
  status = NtCreateEvent (&lf_obj, CYG_EVENT_ACCESS, &attr,
			  NotificationEvent, FALSE);
  if (!NT_SUCCESS (status))
    api_fatal ("NtCreateEvent(lock): %p", status);
}

/* Open a lock event object for SYNCHRONIZE access (to wait for it). */
bool
lockf_t::open_lock_obj ()
{
  WCHAR name[LOCK_OBJ_NAME_LEN + 1];
  UNICODE_STRING uname;
  OBJECT_ATTRIBUTES attr;
  NTSTATUS status;

  __small_swprintf (name, L"%02x-%01x-%016X-%016X-%016X-%08x",
			  lf_flags & (F_POSIX | F_FLOCK), lf_type, lf_start,
			  lf_end, lf_id, lf_wid);
  RtlInitCountedUnicodeString (&uname, name,
			       LOCK_OBJ_NAME_LEN * sizeof (WCHAR));
  InitializeObjectAttributes (&attr, &uname, 0, lf_inode->i_dir, NULL);
  status = NtOpenEvent (&lf_obj, FLOCK_EVENT_ACCESS, &attr);
  if (!NT_SUCCESS (status))
    {
      SetLastError (RtlNtStatusToDosError (status));
      lf_obj = NULL; /* Paranoia... */
    }
  return lf_obj != NULL;
}

/* Close a lock event handle.  The important thing here is to signal it
   before closing the handle.  This way all threads waiting for this
   lock can wake up. */
void
lockf_t::del_lock_obj (HANDLE fhdl, bool signal)
{
  if (lf_obj)
    {
      /* Only signal the event if it's either a POSIX lock, or, in case of
	 BSD flock locks, if it's an explicit unlock or if the calling fhandler
	 holds the last reference to the file table entry.  The file table
	 entry in UNIX terms is equivalent to the FILE_OBJECT in Windows NT
	 terms.  It's what the handle/descriptor references when calling
	 CreateFile/open.  Calling DuplicateHandle/dup only creates a new
	 handle/descriptor to the same FILE_OBJECT/file table entry. */
      if ((lf_flags & F_POSIX) || signal
	  || (fhdl && get_obj_handle_count (fhdl) <= 1))
	SetEvent (lf_obj);
      NtClose (lf_obj);
      lf_obj = NULL;
    }
}

lockf_t::~lockf_t ()
{
  del_lock_obj (NULL);
}

/*
 * This variable controls the maximum number of processes that will
 * be checked in doing deadlock detection.
 */
#ifndef __CYGWIN__
#define MAXDEPTH 50
static int maxlockdepth = MAXDEPTH;
#endif

#define NOLOCKF (struct lockf_t *)0
#define SELF    0x1
#define OTHERS  0x2
static int      lf_clearlock (lockf_t *, lockf_t **, HANDLE);
static int      lf_findoverlap (lockf_t *, lockf_t *, int, lockf_t ***, lockf_t **);
static lockf_t *lf_getblock (lockf_t *, inode_t *node);
static int      lf_getlock (lockf_t *, inode_t *, struct __flock64 *);
static int      lf_setlock (lockf_t *, inode_t *, lockf_t **, HANDLE);
static void     lf_split (lockf_t *, lockf_t *, lockf_t **);
static void     lf_wakelock (lockf_t *, HANDLE);

int
fhandler_disk_file::lock (int a_op, struct __flock64 *fl)
{
  _off64_t start, end, oadd;
  lockf_t *n;
  int error = 0;

  short a_flags = fl->l_type & (F_POSIX | F_FLOCK);
  short type = fl->l_type & (F_RDLCK | F_WRLCK | F_UNLCK);

  if (!a_flags)
    a_flags = F_POSIX; /* default */
  if (a_op == F_SETLKW)
    {
      a_op = F_SETLK;
      a_flags |= F_WAIT;
    }
  if (a_op == F_SETLK)
    switch (type)
      {
      case F_UNLCK:
	a_op = F_UNLCK;
	break;
      case F_RDLCK:
	/* flock semantics don't specify a requirement that the file has
	   been opened with a specific open mode, in contrast to POSIX locks
	   which require that a file is opened for reading to place a read
	   lock and opened for writing to place a write lock. */
	if ((a_flags & F_POSIX) && !(get_access () & GENERIC_READ))
	  {
	    set_errno (EBADF);
	    return -1;
	  }
	break;
      case F_WRLCK:
	/* See above comment. */
	if ((a_flags & F_POSIX) && !(get_access () & GENERIC_WRITE))
	  {
	    set_errno (EBADF);
	    return -1;
	  }
	break;
      default:
	set_errno (EINVAL);
	return -1;
      }

  /*
   * Convert the flock structure into a start and end.
   */
  switch (fl->l_whence)
    {
    case SEEK_SET:
      start = fl->l_start;
      break;

    case SEEK_CUR:
      if ((start = lseek (0, SEEK_CUR)) == ILLEGAL_SEEK)
	return -1;
      break;

    case SEEK_END:
      {
	NTSTATUS status;
	IO_STATUS_BLOCK io;
	FILE_STANDARD_INFORMATION fsi;

	status = NtQueryInformationFile (get_handle (), &io, &fsi, sizeof fsi,
					 FileStandardInformation);
	if (!NT_SUCCESS (status))
	  {
	    __seterrno_from_nt_status (status);
	    return -1;
	  }
	if (fl->l_start > 0 && fsi.EndOfFile.QuadPart > OFF_MAX - fl->l_start)
	  {
	    set_errno (EOVERFLOW);
	    return -1;
	  }
	start = fsi.EndOfFile.QuadPart + fl->l_start;
      }
      break;

    default:
      return (EINVAL);
    }
  if (start < 0)
    {
      set_errno (EINVAL);
      return -1;
    }
  if (fl->l_len < 0)
    {
      if (start == 0)
	{
	  set_errno (EINVAL);
	  return -1;
	}
      end = start - 1;
      start += fl->l_len;
      if (start < 0)
	{
	  set_errno (EINVAL);
	  return -1;
	}
    }
  else if (fl->l_len == 0)
    end = -1;
  else
    {
      oadd = fl->l_len - 1;
      if (oadd > OFF_MAX - start)
	{
	  set_errno (EOVERFLOW);
	  return -1;
	}
      end = start + oadd;
    }

  inode_t *node = inode_t::get (get_dev (), get_ino (), true);
  if (!node)
    {
      set_errno (ENOLCK);
      return -1;
    }
  need_fork_fixup (true);

  /* Unlock the fd table which has been locked in fcntl_worker/lock_worker,
     otherwise a blocking F_SETLKW never wakes up on a signal. */
  cygheap->fdtab.unlock ();

  lockf_t **head = &node->i_lockf;

  /*
   * Avoid the common case of unlocking when inode_t has no locks.
   */
  if (*head == NULL)
    {
      if (a_op != F_SETLK)
	{
	  node->UNLOCK ();
	  fl->l_type = F_UNLCK;
	  return 0;
	}
    }
  /*
   * Allocate a spare structure in case we have to split.
   */
  lockf_t *clean = NULL;
  if (a_op == F_SETLK || a_op == F_UNLCK)
    {
      clean = new lockf_t ();
      if (!clean)
	{
	  node->UNLOCK ();
	  set_errno (ENOLCK);
	  return -1;
	}
    }
  /*
   * Create the lockf_t structure
   */
  lockf_t *lock = new lockf_t (node, head, a_flags, type, start, end,
			       (a_flags & F_FLOCK) ? get_unique_id ()
						   : getpid (),
			       myself->dwProcessId);
  if (!lock)
    {
      node->UNLOCK ();
      set_errno (ENOLCK);
      return -1;
    }

  switch (a_op)
    {
    case F_SETLK:
      error = lf_setlock (lock, node, &clean, get_handle ());
      break;

    case F_UNLCK:
      error = lf_clearlock (lock, &clean, get_handle ());
      lock->lf_next = clean;
      clean = lock;
      break;

    case F_GETLK:
      error = lf_getlock (lock, node, fl);
      lock->lf_next = clean;
      clean = lock;
      break;

    default:
      lock->lf_next = clean;
      clean = lock;
      error = EINVAL;
      break;
    }
  for (lock = clean; lock != NULL; )
    {
      n = lock->lf_next;
      lock->del_lock_obj (get_handle (), a_op == F_UNLCK);
      delete lock;
      lock = n;
    }
  if (node->i_lockf == NULL && !node->waiting ())
    {
      INODE_LIST_LOCK ();
      LIST_REMOVE (node, i_next);
      node->UNLOCK ();
      delete node;
      INODE_LIST_UNLOCK ();
    }
  else
    node->UNLOCK ();
  if (error)
    {
      set_errno (error);
      return -1;
    }
  return 0;
}

/*
 * Set a byte-range lock.
 */
static int
lf_setlock (lockf_t *lock, inode_t *node, lockf_t **clean, HANDLE fhdl)
{
  lockf_t *block;
  lockf_t **head = lock->lf_head;
  lockf_t **prev, *overlap;
  int ovcase, priority, old_prio, needtolink;
  tmp_pathbuf tp;

  /*
   * Set the priority
   */
  priority = old_prio = GetThreadPriority (GetCurrentThread ());
  if (lock->lf_type == F_WRLCK && priority <= THREAD_PRIORITY_ABOVE_NORMAL)
    priority = THREAD_PRIORITY_HIGHEST;
  /*
   * Scan lock list for this file looking for locks that would block us.
   */
  /* Create temporary space for the all locks list. */
  node->i_all_lf = (lockf_t *) tp.w_get ();
  while ((block = lf_getblock(lock, node)))
    {
      DWORD ret;
      HANDLE obj = block->lf_obj;
      block->lf_obj = NULL;

      /*
       * Free the structure and return if nonblocking.
       */
      if ((lock->lf_flags & F_WAIT) == 0)
	{
	  lock->lf_next = *clean;
	  *clean = lock;
	  if (obj)
	    NtClose (obj);
	  return EAGAIN;
	}
      /*
       * We are blocked. Since flock style locks cover
       * the whole file, there is no chance for deadlock.
       * For byte-range locks we must check for deadlock.
       *
       * Deadlock detection is done by looking through the
       * wait channels to see if there are any cycles that
       * involve us. MAXDEPTH is set just to make sure we
       * do not go off into neverland.
       */
      /* FIXME: We check the handle count of all the lock event objects
		this process holds.  If it's > 1, another process is
		waiting for one of our locks.  This method isn't overly
		intelligent.  If it turns out to be too dumb, we might
		have to remove it or to find another method. */
      for (lockf_t *lk = node->i_lockf; lk; lk = lk->lf_next)
	if ((lk->lf_flags & F_POSIX) && get_obj_handle_count (lk->lf_obj) > 1)
	  {
	    if (obj)
	      NtClose (obj);
	    return EDEADLK;
	  }

      /*
       * For flock type locks, we must first remove
       * any shared locks that we hold before we sleep
       * waiting for an exclusive lock.
       */
      if ((lock->lf_flags & F_FLOCK) && lock->lf_type == F_WRLCK)
	{
	  lock->lf_type = F_UNLCK;
	  (void) lf_clearlock (lock, clean, fhdl);
	  lock->lf_type = F_WRLCK;
	}

      /*
       * Add our lock to the blocked list and sleep until we're free.
       * Remember who blocked us (for deadlock detection).
       */
      /* Cygwin:  No locked list.  See deadlock recognition above. */

      /* Wait for the blocking object and its holding process. */
      if (!obj)
	{
	  /* We can't synchronize on the lock event object.
	     Treat this as a deadlock-like situation for now. */
	  system_printf ("Can't sync with lock object hold by "
			 "Win32 pid %lu: %E", block->lf_wid);
	  return EDEADLK;
	}
      SetThreadPriority (GetCurrentThread (), priority);
      if (lock->lf_flags & F_POSIX)
	{
	  HANDLE proc = OpenProcess (SYNCHRONIZE, FALSE, block->lf_wid);
	  if (!proc)
	    {
	      /* If we can't synchronize on the process holding the lock,
		 we will never recognize when the lock has been abandoned.
		 Treat this as a deadlock-like situation for now. */
	      system_printf ("Can't sync with process holding a lock "
			     "(Win32 pid %lu): %E", block->lf_wid);
	      NtClose (obj);
	      return EDEADLK;
	    }
	  HANDLE w4[3] = { obj, proc, signal_arrived };
	  node->wait ();
	  node->UNLOCK ();
	  ret = WaitForMultipleObjects (3, w4, FALSE, INFINITE);
	  CloseHandle (proc);
	}
      else
	{
	  HANDLE w4[2] = { obj, signal_arrived };
	  node->wait ();
	  node->UNLOCK ();
	  /* Unfortunately, since BSD flock locks are not attached to a
	     specific process, we can't recognize an abandoned lock by
	     sync'ing with a process.  We have to find out if we're the only
	     process left accessing this event object. */
	  do
	    {
	      ret = WaitForMultipleObjects (2, w4, FALSE, 100L);
	    }
	  while (ret == WAIT_TIMEOUT && get_obj_handle_count (obj) > 1);
	  /* There's a good chance that the above loop is left with
	     ret == WAIT_TIMEOUT if another process closes the file handle
	     associated with this lock.  This is for all practical purposes
	     equivalent to a signalled lock object. */
	  if (ret == WAIT_TIMEOUT)
	    ret = WAIT_OBJECT_0;
	}
      node->LOCK ();
      node->unwait ();
      NtClose (obj);
      SetThreadPriority (GetCurrentThread (), old_prio);
      switch (ret)
	{
	case WAIT_OBJECT_0:
	  /* The lock object has been set to signalled. */
	  break;
	case WAIT_OBJECT_0 + 1:
	  /* For POSIX locks, the process holding the lock has exited. */
	  if (lock->lf_flags & F_POSIX)
	    break;
	  /*FALLTHRU*/
	case WAIT_OBJECT_0 + 2:
	  /* A signal came in. */
	  _my_tls.call_signal_handler ();
	  return EINTR;
	default:
	  system_printf ("Shouldn't happen! ret = %lu, error: %lu\n",
			 ret, GetLastError ());
	  return geterrno_from_win_error ();
	}
    }
  allow_others_to_sync ();
  /*
   * No blocks!!  Add the lock.  Note that we will
   * downgrade or upgrade any overlapping locks this
   * process already owns.
   *
   * Handle any locks that overlap.
   */
  prev = head;
  block = *head;
  needtolink = 1;
  for (;;)
    {
      ovcase = lf_findoverlap (block, lock, SELF, &prev, &overlap);
      if (ovcase)
	block = overlap->lf_next;
      /*
       * Six cases:
       *  0) no overlap
       *  1) overlap == lock
       *  2) overlap contains lock
       *  3) lock contains overlap
       *  4) overlap starts before lock
       *  5) overlap ends after lock
       */
      switch (ovcase)
	{
	case 0: /* no overlap */
	  if (needtolink)
	    {
	      *prev = lock;
	      lock->lf_next = overlap;
	      lock->create_lock_obj ();
	    }
	    break;

	case 1: /* overlap == lock */
	  /*
	   * If downgrading lock, others may be
	   * able to acquire it.
	   * Cygwin: Always wake lock.
	   */
	  lf_wakelock (overlap, fhdl);
	  overlap->lf_type = lock->lf_type;
	  overlap->create_lock_obj ();
	  lock->lf_next = *clean;
	  *clean = lock;
	  break;

	case 2: /* overlap contains lock */
	  /*
	   * Check for common starting point and different types.
	   */
	  if (overlap->lf_type == lock->lf_type)
	    {
	      lock->lf_next = *clean;
	      *clean = lock;
	      break;
	    }
	  if (overlap->lf_start == lock->lf_start)
	    {
	      *prev = lock;
	      lock->lf_next = overlap;
	      overlap->lf_start = lock->lf_end + 1;
	    }
	  else
	    lf_split (overlap, lock, clean);
	  lf_wakelock (overlap, fhdl);
	  overlap->create_lock_obj ();
	  lock->create_lock_obj ();
	  if (lock->lf_next && !lock->lf_next->lf_obj)
	    lock->lf_next->create_lock_obj ();
	  break;

	case 3: /* lock contains overlap */
	  /*
	   * If downgrading lock, others may be able to
	   * acquire it, otherwise take the list.
	   * Cygwin: Always wake old lock and create new lock.
	   */
	  lf_wakelock (overlap, fhdl);
	  /*
	   * Add the new lock if necessary and delete the overlap.
	   */
	  if (needtolink)
	    {
	      *prev = lock;
	      lock->lf_next = overlap->lf_next;
	      prev = &lock->lf_next;
	      lock->create_lock_obj ();
	      needtolink = 0;
	    }
	  else
	    *prev = overlap->lf_next;
	  overlap->lf_next = *clean;
	  *clean = overlap;
	  continue;

	case 4: /* overlap starts before lock */
	  /*
	   * Add lock after overlap on the list.
	   */
	  lock->lf_next = overlap->lf_next;
	  overlap->lf_next = lock;
	  overlap->lf_end = lock->lf_start - 1;
	  prev = &lock->lf_next;
	  lf_wakelock (overlap, fhdl);
	  overlap->create_lock_obj ();
	  lock->create_lock_obj ();
	  needtolink = 0;
	  continue;

	case 5: /* overlap ends after lock */
	  /*
	   * Add the new lock before overlap.
	   */
	  if (needtolink) {
	      *prev = lock;
	      lock->lf_next = overlap;
	  }
	  overlap->lf_start = lock->lf_end + 1;
	  lf_wakelock (overlap, fhdl);
	  lock->create_lock_obj ();
	  overlap->create_lock_obj ();
	  break;
	}
      break;
    }
  return 0;
}

/*
 * Remove a byte-range lock on an inode_t.
 *
 * Generally, find the lock (or an overlap to that lock)
 * and remove it (or shrink it), then wakeup anyone we can.
 */
static int
lf_clearlock (lockf_t *unlock, lockf_t **clean, HANDLE fhdl)
{
  lockf_t **head = unlock->lf_head;
  lockf_t *lf = *head;
  lockf_t *overlap, **prev;
  int ovcase;

  if (lf == NOLOCKF)
    return 0;
  prev = head;
  while ((ovcase = lf_findoverlap (lf, unlock, SELF, &prev, &overlap)))
    {
      /*
       * Wakeup the list of locks to be retried.
       */
      lf_wakelock (overlap, fhdl);

      switch (ovcase)
	{
	case 1: /* overlap == lock */
	  *prev = overlap->lf_next;
	  overlap->lf_next = *clean;
	  *clean = overlap;
	  break;

	case 2: /* overlap contains lock: split it */
	  if (overlap->lf_start == unlock->lf_start)
	    {
	      overlap->lf_start = unlock->lf_end + 1;
	      overlap->create_lock_obj ();
	      break;
	    }
	  lf_split (overlap, unlock, clean);
	  overlap->lf_next = unlock->lf_next;
	  overlap->create_lock_obj ();
	  if (overlap->lf_next && !overlap->lf_next->lf_obj)
	    overlap->lf_next->create_lock_obj ();
	  break;

	case 3: /* lock contains overlap */
	  *prev = overlap->lf_next;
	  lf = overlap->lf_next;
	  overlap->lf_next = *clean;
	  *clean = overlap;
	  continue;

	case 4: /* overlap starts before lock */
	    overlap->lf_end = unlock->lf_start - 1;
	    prev = &overlap->lf_next;
	    lf = overlap->lf_next;
	    overlap->create_lock_obj ();
	    continue;

	case 5: /* overlap ends after lock */
	    overlap->lf_start = unlock->lf_end + 1;
	    overlap->create_lock_obj ();
	    break;
	}
      break;
    }
  return 0;
}

/*
 * Check whether there is a blocking lock,
 * and if so return its process identifier.
 */
static int
lf_getlock (lockf_t *lock, inode_t *node, struct __flock64 *fl)
{
  lockf_t *block;
  tmp_pathbuf tp;

  /* Create temporary space for the all locks list. */
  node->i_all_lf = (lockf_t *) tp.w_get ();
  if ((block = lf_getblock (lock, node)))
    {
      if (block->lf_obj)
	NtClose (block->lf_obj);
      fl->l_type = block->lf_type;
      fl->l_whence = SEEK_SET;
      fl->l_start = block->lf_start;
      if (block->lf_end == -1)
	fl->l_len = 0;
      else
	fl->l_len = block->lf_end - block->lf_start + 1;
      if (block->lf_flags & F_POSIX)
	fl->l_pid = (pid_t) block->lf_id;
      else
	fl->l_pid = -1;
    }
  else
    fl->l_type = F_UNLCK;
  return 0;
}

/*
 * Walk the list of locks for an inode_t and
 * return the first blocking lock.
 */
static lockf_t *
lf_getblock (lockf_t *lock, inode_t *node)
{
  lockf_t **prev, *overlap;
  lockf_t *lf = node->get_all_locks_list ();
  int ovcase;
  NTSTATUS status;
  EVENT_BASIC_INFORMATION ebi;

  prev = lock->lf_head;
  while ((ovcase = lf_findoverlap (lf, lock, OTHERS, &prev, &overlap)))
    {
      /*
       * We've found an overlap, see if it blocks us
       */
      if ((lock->lf_type == F_WRLCK || overlap->lf_type == F_WRLCK))
	{
	  /* Open the event object for synchronization. */
	  if (!overlap->open_lock_obj () || (overlap->lf_flags & F_POSIX))
	    return overlap;
	  /* In case of BSD flock locks, check if the event object is
	     signalled.  If so, the overlap doesn't actually exist anymore.
	     There are just a few open handles left. */
	  status = NtQueryEvent (overlap->lf_obj, EventBasicInformation,
				 &ebi, sizeof ebi, NULL);
	  if (!NT_SUCCESS (status) || ebi.SignalState == 0)
	    return overlap;
	  NtClose (overlap->lf_obj);
	  overlap->lf_obj = NULL;
	}
      /*
       * Nope, point to the next one on the list and
       * see if it blocks us
       */
      lf = overlap->lf_next;
    }
  return NOLOCKF;
}

/*
 * Walk the list of locks for an inode_t to
 * find an overlapping lock (if any).
 *
 * NOTE: this returns only the FIRST overlapping lock.  There
 *   may be more than one.
 */
static int
lf_findoverlap (lockf_t *lf, lockf_t *lock, int type, lockf_t ***prev,
		lockf_t **overlap)
{
  _off64_t start, end;

  *overlap = lf;
  if (lf == NOLOCKF)
    return 0;

  start = lock->lf_start;
  end = lock->lf_end;
  while (lf != NOLOCKF)
    {
      if (((type & SELF) && lf->lf_id != lock->lf_id)
	  || ((type & OTHERS) && lf->lf_id == lock->lf_id)
	  /* As on Linux: POSIX locks and BSD flock locks don't interact. */
	  || (lf->lf_flags & (F_POSIX | F_FLOCK))
	     != (lock->lf_flags & (F_POSIX | F_FLOCK)))
	{
	  *prev = &lf->lf_next;
	  *overlap = lf = lf->lf_next;
	  continue;
	}
      /*
       * OK, check for overlap
       *
       * Six cases:
       *  0) no overlap
       *  1) overlap == lock
       *  2) overlap contains lock
       *  3) lock contains overlap
       *  4) overlap starts before lock
       *  5) overlap ends after lock
       */
      if ((lf->lf_end != -1 && start > lf->lf_end) ||
	  (end != -1 && lf->lf_start > end))
	{
	  /* Case 0 */
	  if ((type & SELF) && end != -1 && lf->lf_start > end)
	    return 0;
	  *prev = &lf->lf_next;
	  *overlap = lf = lf->lf_next;
	  continue;
	}
      if ((lf->lf_start == start) && (lf->lf_end == end))
	{
	  /* Case 1 */
	  return 1;
	}
      if ((lf->lf_start <= start) && (end != -1) &&
	  ((lf->lf_end >= end) || (lf->lf_end == -1)))
	{
	  /* Case 2 */
	  return 2;
	}
      if (start <= lf->lf_start && (end == -1 ||
	  (lf->lf_end != -1 && end >= lf->lf_end)))
	{
	  /* Case 3 */
	  return 3;
	}
      if ((lf->lf_start < start) &&
	  ((lf->lf_end >= start) || (lf->lf_end == -1)))
	{
	  /* Case 4 */
	  return 4;
	}
      if ((lf->lf_start > start) && (end != -1) &&
	  ((lf->lf_end > end) || (lf->lf_end == -1)))
	{
	  /* Case 5 */
	  return 5;
	}
      api_fatal ("lf_findoverlap: default\n");
    }
  return 0;
}

/*
 * Split a lock and a contained region into
 * two or three locks as necessary.
 */
static void
lf_split (lockf_t *lock1, lockf_t *lock2, lockf_t **split)
{
  lockf_t *splitlock;

  /*
   * Check to see if spliting into only two pieces.
   */
  if (lock1->lf_start == lock2->lf_start)
    {
      lock1->lf_start = lock2->lf_end + 1;
      lock2->lf_next = lock1;
      return;
    }
  if (lock1->lf_end == lock2->lf_end)
    {
      lock1->lf_end = lock2->lf_start - 1;
      lock2->lf_next = lock1->lf_next;
      lock1->lf_next = lock2;
      return;
    }
  /*
   * Make a new lock consisting of the last part of
   * the encompassing lock.  We use the preallocated
   * splitlock so we don't have to block.
   */
  splitlock = *split;
  assert (splitlock != NULL);
  *split = splitlock->lf_next;
  memcpy (splitlock, lock1, sizeof *splitlock);
  /* We have to unset the obj HANDLE here which has been copied by the
     above memcpy, so that the calling function recognizes the new object.
     See post-lf_split handling in lf_setlock and lf_clearlock. */
  splitlock->lf_obj = NULL;
  splitlock->lf_start = lock2->lf_end + 1;
  lock1->lf_end = lock2->lf_start - 1;
  /*
   * OK, now link it in
   */
  splitlock->lf_next = lock1->lf_next;
  lock2->lf_next = splitlock;
  lock1->lf_next = lock2;
}

/*
 * Wakeup a blocklist
 * Cygwin: Just signal the lock which gets removed.  This unblocks
 * all threads waiting for this lock.
 */
static void
lf_wakelock (lockf_t *listhead, HANDLE fhdl)
{
  listhead->del_lock_obj (fhdl, true);
}

extern "C" int
flock (int fd, int operation)
{
  int res = -1;
  int cmd;
  struct __flock64 fl = { 0, SEEK_SET, 0, 0, 0 };

  myfault efault;
  if (efault.faulted (EFAULT))
    return -1;

  cygheap_fdget cfd (fd, true);
  if (cfd < 0)
    goto done;

  cmd = (operation & LOCK_NB) ? F_SETLK : F_SETLKW;
  switch (operation & (~LOCK_NB))
    {
    case LOCK_EX:
      fl.l_type = F_WRLCK | F_FLOCK;
      break;
    case LOCK_SH:
      fl.l_type = F_RDLCK | F_FLOCK;
      break;
    case LOCK_UN:
      fl.l_type = F_UNLCK | F_FLOCK;
      break;
    default:
      set_errno (EINVAL);
      goto done;
    }
  res = cfd->lock (cmd, &fl);
  if ((res == -1) && ((get_errno () == EAGAIN) || (get_errno () == EACCES)))
    set_errno (EWOULDBLOCK);
done:
  syscall_printf ("%d = flock (%d, %d)", res, fd, operation);
  return res;
}

extern "C" int
lockf (int filedes, int function, _off64_t size)
{
  int res = -1;
  int cmd;
  struct __flock64 fl;

  myfault efault;
  if (efault.faulted (EFAULT))
    return -1;

  cygheap_fdget cfd (filedes, true);
  if (cfd < 0)
    goto done;

  fl.l_start = 0;
  fl.l_len = size;
  fl.l_whence = SEEK_CUR;

  switch (function)
    {
    case F_ULOCK:
      cmd = F_SETLK;
      fl.l_type = F_UNLCK;
      break;
    case F_LOCK:
      cmd = F_SETLKW;
      fl.l_type = F_WRLCK;
      break;
    case F_TLOCK:
      cmd = F_SETLK;
      fl.l_type = F_WRLCK;
      break;
    case F_TEST:
      fl.l_type = F_WRLCK;
      if (cfd->lock (F_GETLK, &fl) == -1)
	goto done;
      if (fl.l_type == F_UNLCK || fl.l_pid == getpid ())
	res = 0;
      else
	errno = EAGAIN;
      goto done;
      /* NOTREACHED */
    default:
      errno = EINVAL;
      goto done;
      /* NOTREACHED */
    }
  res = cfd->lock (cmd, &fl);
done:
  syscall_printf ("%d = lockf (%d, %d, %D)", res, filedes, function, size);
  return res;
}