diff --git a/dlls/kernel/tests/file.c b/dlls/kernel/tests/file.c
index 02177e90b95..3a0ecc60a81 100644
--- a/dlls/kernel/tests/file.c
+++ b/dlls/kernel/tests/file.c
@@ -674,6 +674,79 @@ void test_offset_in_overlapped_structure(void)
     ok(DeleteFileA(temp_fname), "DeleteFileA error %ld\n", GetLastError());
 }
 
+static void test_LockFile(void)
+{
+    HANDLE handle;
+    DWORD written;
+    OVERLAPPED overlapped;
+
+    handle = CreateFileA( filename, GENERIC_READ | GENERIC_WRITE,
+                          FILE_SHARE_READ | FILE_SHARE_WRITE, NULL,
+                          CREATE_ALWAYS, 0, 0 );
+    if (handle == INVALID_HANDLE_VALUE)
+    {
+        ok(0,"couldn't create file \"%s\" (err=%ld)",filename,GetLastError());
+        return;
+    }
+    ok( WriteFile( handle, sillytext, strlen(sillytext), &written, NULL ), "write failed" );
+
+    ok( LockFile( handle, 0, 0, 0, 0 ), "LockFile failed" );
+    ok( UnlockFile( handle, 0, 0, 0, 0 ), "UnlockFile failed" );
+    ok( !UnlockFile( handle, 0, 0, 0, 0 ), "UnlockFile succeeded" );
+
+    ok( LockFile( handle, 10, 0, 20, 0 ), "LockFile 10,20 failed" );
+    /* overlapping locks must fail */
+    ok( !LockFile( handle, 12, 0, 10, 0 ), "LockFile 12,10 succeeded" );
+    ok( !LockFile( handle, 5, 0, 6, 0 ), "LockFile 5,6 succeeded" );
+    /* non-overlapping locks must succeed */
+    ok( LockFile( handle, 5, 0, 5, 0 ), "LockFile 5,5 failed" );
+
+    ok( !UnlockFile( handle, 10, 0, 10, 0 ), "UnlockFile 10,10 succeeded" );
+    ok( UnlockFile( handle, 10, 0, 20, 0 ), "UnlockFile 10,20 failed" );
+    ok( !UnlockFile( handle, 10, 0, 20, 0 ), "UnlockFile 10,20 again succeeded" );
+    ok( UnlockFile( handle, 5, 0, 5, 0 ), "UnlockFile 5,5 failed" );
+
+    overlapped.Offset = 100;
+    overlapped.OffsetHigh = 0;
+    overlapped.hEvent = 0;
+    ok( LockFileEx( handle, 0, 0, 100, 0, &overlapped ), "LockFileEx 100,100 failed" );
+    /* overlapping shared locks are OK */
+    overlapped.Offset = 150;
+    ok( LockFileEx( handle, 0, 0, 100, 0, &overlapped ), "LockFileEx 150,100 failed" );
+    /* but exclusive is not */
+    ok( !LockFileEx( handle, LOCKFILE_EXCLUSIVE_LOCK|LOCKFILE_FAIL_IMMEDIATELY, 0, 50, 0, &overlapped ),
+        "LockFileEx exclusive 150,50 succeeded" );
+    ok( UnlockFileEx( handle, 0, 100, 0, &overlapped ), "UnlockFileEx 150,100 failed" );
+    ok( !UnlockFileEx( handle, 0, 100, 0, &overlapped ), "UnlockFileEx 150,100 again succeeded" );
+    overlapped.Offset = 100;
+    ok( UnlockFileEx( handle, 0, 100, 0, &overlapped ), "UnlockFileEx 100,100 failed" );
+    ok( !UnlockFileEx( handle, 0, 100, 0, &overlapped ), "UnlockFileEx 100,100 again succeeded" );
+
+    ok( LockFile( handle, 0, 0x10000000, 0, 0xf0000000 ), "LockFile failed" );
+    ok( !LockFile( handle, ~0, ~0, 1, 0 ), "LockFile ~0,1 succeeded" );
+    ok( !LockFile( handle, 0, 0x20000000, 20, 0 ), "LockFile 0x20000000,20 succeeded" );
+    ok( UnlockFile( handle, 0, 0x10000000, 0, 0xf0000000 ), "UnlockFile failed" );
+
+    /* wrap-around lock should not do anything */
+    /* (but still succeeds on NT4 so we don't check result) */
+    LockFile( handle, 0, 0x10000000, 0, 0xf0000001 );
+    ok( LockFile( handle, ~0, ~0, 1, 0 ), "LockFile ~0,1 failed" );
+    ok( UnlockFile( handle, ~0, ~0, 1, 0 ), "Unlockfile ~0,1 failed" );
+
+    /* zero-byte lock */
+    ok( LockFile( handle, 100, 0, 0, 0 ), "LockFile 100,0 failed" );
+    ok( !LockFile( handle, 98, 0, 4, 0 ), "LockFile 98,4 succeeded" );
+    ok( LockFile( handle, 90, 0, 10, 0 ), "LockFile 90,10 failed" );
+    ok( LockFile( handle, 100, 0, 10, 0 ), "LockFile 100,10 failed" );
+    ok( UnlockFile( handle, 90, 0, 10, 0 ), "UnlockFile 90,10 failed" );
+    ok( UnlockFile( handle, 100, 0, 10, 0 ), "UnlockFile 100,10 failed" );
+    ok( UnlockFile( handle, 100, 0, 0, 0 ), "UnlockFile 100,0 failed" );
+
+    CloseHandle( handle );
+    DeleteFileA( filename );
+}
+
+
 START_TEST(file)
 {
     test__hread(  );
@@ -690,5 +763,6 @@ START_TEST(file)
     test_CreateFileW();
     test_DeleteFileA();
     test_DeleteFileW();
+    test_LockFile();
     test_offset_in_overlapped_structure();
 }
diff --git a/files/file.c b/files/file.c
index 78a8bf3c6ee..0313936bbe9 100644
--- a/files/file.c
+++ b/files/file.c
@@ -2995,20 +2995,22 @@ BOOL WINAPI SetFileTime( HANDLE hFile,
 /**************************************************************************
  *           LockFile   (KERNEL32.@)
  */
-BOOL WINAPI LockFile( HANDLE hFile, DWORD dwFileOffsetLow, DWORD dwFileOffsetHigh,
-                        DWORD nNumberOfBytesToLockLow, DWORD nNumberOfBytesToLockHigh )
+BOOL WINAPI LockFile( HANDLE hFile, DWORD offset_low, DWORD offset_high,
+                      DWORD count_low, DWORD count_high )
 {
     BOOL ret;
 
-    FIXME("not implemented in server\n");
+    TRACE( "%p %lx%08lx %lx%08lx\n", hFile, offset_high, offset_low, count_high, count_low );
 
     SERVER_START_REQ( lock_file )
     {
         req->handle      = hFile;
-        req->offset_low  = dwFileOffsetLow;
-        req->offset_high = dwFileOffsetHigh;
-        req->count_low   = nNumberOfBytesToLockLow;
-        req->count_high  = nNumberOfBytesToLockHigh;
+        req->offset_low  = offset_low;
+        req->offset_high = offset_high;
+        req->count_low   = count_low;
+        req->count_high  = count_high;
+        req->shared      = FALSE;
+        req->wait        = FALSE;
         ret = !wine_server_call_err( req );
     }
     SERVER_END_REQ;
@@ -3028,41 +3030,76 @@ BOOL WINAPI LockFile( HANDLE hFile, DWORD dwFileOffsetLow, DWORD dwFileOffsetHig
  * Per Microsoft docs, the third parameter (reserved) must be set to 0.
  */
 BOOL WINAPI LockFileEx( HANDLE hFile, DWORD flags, DWORD reserved,
-		      DWORD nNumberOfBytesToLockLow, DWORD nNumberOfBytesToLockHigh,
-		      LPOVERLAPPED pOverlapped )
+                        DWORD count_low, DWORD count_high, LPOVERLAPPED overlapped )
 {
-    FIXME("hFile=%p,flags=%ld,reserved=%ld,lowbytes=%ld,highbytes=%ld,overlapped=%p: stub.\n",
-	  hFile, flags, reserved, nNumberOfBytesToLockLow, nNumberOfBytesToLockHigh,
-	  pOverlapped);
-    if (reserved == 0)
-	SetLastError(ERROR_CALL_NOT_IMPLEMENTED);
-    else
+    NTSTATUS err;
+    BOOL async;
+    HANDLE handle;
+
+    if (reserved)
     {
-	ERR("reserved == %ld: Supposed to be 0??\n", reserved);
-	SetLastError(ERROR_INVALID_PARAMETER);
+        SetLastError( ERROR_INVALID_PARAMETER );
+        return FALSE;
     }
 
-    return FALSE;
+    TRACE( "%p %lx%08lx %lx%08lx flags %lx\n",
+           hFile, overlapped->OffsetHigh, overlapped->Offset, count_high, count_low, flags );
+
+    for (;;)
+    {
+        SERVER_START_REQ( lock_file )
+        {
+            req->handle      = hFile;
+            req->offset_low  = overlapped->Offset;
+            req->offset_high = overlapped->OffsetHigh;
+            req->count_low   = count_low;
+            req->count_high  = count_high;
+            req->shared      = !(flags & LOCKFILE_EXCLUSIVE_LOCK);
+            req->wait        = !(flags & LOCKFILE_FAIL_IMMEDIATELY);
+            err = wine_server_call( req );
+            handle = reply->handle;
+            async  = reply->overlapped;
+        }
+        SERVER_END_REQ;
+        if (err != STATUS_PENDING)
+        {
+            if (err) SetLastError( RtlNtStatusToDosError(err) );
+            return !err;
+        }
+        if (async)
+        {
+            FIXME( "Async I/O lock wait not implemented, might deadlock\n" );
+            if (handle) CloseHandle( handle );
+            SetLastError( ERROR_IO_PENDING );
+            return FALSE;
+        }
+        if (handle)
+        {
+            WaitForSingleObject( handle, INFINITE );
+            CloseHandle( handle );
+        }
+        else Sleep(100);  /* Unix lock conflict, sleep a bit and retry */
+    }
 }
 
 
 /**************************************************************************
  *           UnlockFile   (KERNEL32.@)
  */
-BOOL WINAPI UnlockFile( HANDLE hFile, DWORD dwFileOffsetLow, DWORD dwFileOffsetHigh,
-                          DWORD nNumberOfBytesToUnlockLow, DWORD nNumberOfBytesToUnlockHigh )
+BOOL WINAPI UnlockFile( HANDLE hFile, DWORD offset_low, DWORD offset_high,
+                        DWORD count_low, DWORD count_high )
 {
     BOOL ret;
 
-    FIXME("not implemented in server\n");
+    TRACE( "%p %lx%08lx %lx%08lx\n", hFile, offset_high, offset_low, count_high, count_low );
 
     SERVER_START_REQ( unlock_file )
     {
         req->handle      = hFile;
-        req->offset_low  = dwFileOffsetLow;
-        req->offset_high = dwFileOffsetHigh;
-        req->count_low   = nNumberOfBytesToUnlockLow;
-        req->count_high  = nNumberOfBytesToUnlockHigh;
+        req->offset_low  = offset_low;
+        req->offset_high = offset_high;
+        req->count_low   = count_low;
+        req->count_high  = count_high;
         ret = !wine_server_call_err( req );
     }
     SERVER_END_REQ;
@@ -3073,221 +3110,17 @@ BOOL WINAPI UnlockFile( HANDLE hFile, DWORD dwFileOffsetLow, DWORD dwFileOffsetH
 /**************************************************************************
  *           UnlockFileEx   (KERNEL32.@)
  */
-BOOL WINAPI UnlockFileEx(
-		HANDLE hFile,
-		DWORD dwReserved,
-		DWORD nNumberOfBytesToUnlockLow,
-		DWORD nNumberOfBytesToUnlockHigh,
-		LPOVERLAPPED lpOverlapped
-)
+BOOL WINAPI UnlockFileEx( HANDLE hFile, DWORD reserved, DWORD count_low, DWORD count_high,
+                          LPOVERLAPPED overlapped )
 {
-	FIXME("hFile=%p,reserved=%ld,lowbytes=%ld,highbytes=%ld,overlapped=%p: stub.\n",
-	  hFile, dwReserved, nNumberOfBytesToUnlockLow, nNumberOfBytesToUnlockHigh,
-	  lpOverlapped);
-	if (dwReserved == 0)
-		SetLastError(ERROR_CALL_NOT_IMPLEMENTED);
-	else
-	{
-		ERR("reserved == %ld: Supposed to be 0??\n", dwReserved);
-		SetLastError(ERROR_INVALID_PARAMETER);
-	}
-
-	return FALSE;
-}
-
-
-#if 0
-
-struct DOS_FILE_LOCK {
-  struct DOS_FILE_LOCK *	next;
-  DWORD				base;
-  DWORD				len;
-  DWORD				processId;
-  FILE_OBJECT *			dos_file;
-/*  char *			unix_name;*/
-};
-
-typedef struct DOS_FILE_LOCK DOS_FILE_LOCK;
-
-static DOS_FILE_LOCK *locks = NULL;
-static void DOS_RemoveFileLocks(FILE_OBJECT *file);
-
-
-/* Locks need to be mirrored because unix file locking is based
- * on the pid. Inside of wine there can be multiple WINE processes
- * that share the same unix pid.
- * Read's and writes should check these locks also - not sure
- * how critical that is at this point (FIXME).
- */
-
-static BOOL DOS_AddLock(FILE_OBJECT *file, struct flock *f)
-{
-  DOS_FILE_LOCK *curr;
-  DWORD		processId;
-
-  processId = GetCurrentProcessId();
-
-  /* check if lock overlaps a current lock for the same file */
-#if 0
-  for (curr = locks; curr; curr = curr->next) {
-    if (strcmp(curr->unix_name, file->unix_name) == 0) {
-      if ((f->l_start == curr->base) && (f->l_len == curr->len))
-	return TRUE;/* region is identic */
-      if ((f->l_start < (curr->base + curr->len)) &&
-	  ((f->l_start + f->l_len) > curr->base)) {
-	/* region overlaps */
-	return FALSE;
-      }
+    if (reserved)
+    {
+        SetLastError( ERROR_INVALID_PARAMETER );
+        return FALSE;
     }
-  }
-#endif
-
-  curr = HeapAlloc( GetProcessHeap(), 0, sizeof(DOS_FILE_LOCK) );
-  curr->processId = GetCurrentProcessId();
-  curr->base = f->l_start;
-  curr->len = f->l_len;
-/*  curr->unix_name = HEAP_strdupA( GetProcessHeap(), 0, file->unix_name);*/
-  curr->next = locks;
-  curr->dos_file = file;
-  locks = curr;
-  return TRUE;
+    return UnlockFile( hFile, overlapped->Offset, overlapped->OffsetHigh, count_low, count_high );
 }
 
-static void DOS_RemoveFileLocks(FILE_OBJECT *file)
-{
-  DWORD		processId;
-  DOS_FILE_LOCK **curr;
-  DOS_FILE_LOCK *rem;
-
-  processId = GetCurrentProcessId();
-  curr = &locks;
-  while (*curr) {
-    if ((*curr)->dos_file == file) {
-      rem = *curr;
-      *curr = (*curr)->next;
-/*      HeapFree( GetProcessHeap(), 0, rem->unix_name );*/
-      HeapFree( GetProcessHeap(), 0, rem );
-    }
-    else
-      curr = &(*curr)->next;
-  }
-}
-
-static BOOL DOS_RemoveLock(FILE_OBJECT *file, struct flock *f)
-{
-  DWORD		processId;
-  DOS_FILE_LOCK **curr;
-  DOS_FILE_LOCK *rem;
-
-  processId = GetCurrentProcessId();
-  for (curr = &locks; *curr; curr = &(*curr)->next) {
-    if ((*curr)->processId == processId &&
-	(*curr)->dos_file == file &&
-	(*curr)->base == f->l_start &&
-	(*curr)->len == f->l_len) {
-      /* this is the same lock */
-      rem = *curr;
-      *curr = (*curr)->next;
-/*      HeapFree( GetProcessHeap(), 0, rem->unix_name );*/
-      HeapFree( GetProcessHeap(), 0, rem );
-      return TRUE;
-    }
-  }
-  /* no matching lock found */
-  return FALSE;
-}
-
-
-/**************************************************************************
- *           LockFile   (KERNEL32.@)
- */
-BOOL WINAPI LockFile(
-	HANDLE hFile,DWORD dwFileOffsetLow,DWORD dwFileOffsetHigh,
-	DWORD nNumberOfBytesToLockLow,DWORD nNumberOfBytesToLockHigh )
-{
-  struct flock f;
-  FILE_OBJECT *file;
-
-  TRACE("handle %d offsetlow=%ld offsethigh=%ld nbyteslow=%ld nbyteshigh=%ld\n",
-	       hFile, dwFileOffsetLow, dwFileOffsetHigh,
-	       nNumberOfBytesToLockLow, nNumberOfBytesToLockHigh);
-
-  if (dwFileOffsetHigh || nNumberOfBytesToLockHigh) {
-    FIXME("Unimplemented bytes > 32bits\n");
-    return FALSE;
-  }
-
-  f.l_start = dwFileOffsetLow;
-  f.l_len = nNumberOfBytesToLockLow;
-  f.l_whence = SEEK_SET;
-  f.l_pid = 0;
-  f.l_type = F_WRLCK;
-
-  if (!(file = FILE_GetFile(hFile,0,NULL))) return FALSE;
-
-  /* shadow locks internally */
-  if (!DOS_AddLock(file, &f)) {
-    SetLastError( ERROR_LOCK_VIOLATION );
-    return FALSE;
-  }
-
-  /* FIXME: Unix locking commented out for now, doesn't work with Excel */
-#ifdef USE_UNIX_LOCKS
-  if (fcntl(file->unix_handle, F_SETLK, &f) == -1) {
-    if (errno == EACCES || errno == EAGAIN) {
-      SetLastError( ERROR_LOCK_VIOLATION );
-    }
-    else {
-      FILE_SetDosError();
-    }
-    /* remove our internal copy of the lock */
-    DOS_RemoveLock(file, &f);
-    return FALSE;
-  }
-#endif
-  return TRUE;
-}
-
-
-/**************************************************************************
- *           UnlockFile   (KERNEL32.@)
- */
-BOOL WINAPI UnlockFile(
-	HANDLE hFile,DWORD dwFileOffsetLow,DWORD dwFileOffsetHigh,
-	DWORD nNumberOfBytesToUnlockLow,DWORD nNumberOfBytesToUnlockHigh )
-{
-  FILE_OBJECT *file;
-  struct flock f;
-
-  TRACE("handle %d offsetlow=%ld offsethigh=%ld nbyteslow=%ld nbyteshigh=%ld\n",
-	       hFile, dwFileOffsetLow, dwFileOffsetHigh,
-	       nNumberOfBytesToUnlockLow, nNumberOfBytesToUnlockHigh);
-
-  if (dwFileOffsetHigh || nNumberOfBytesToUnlockHigh) {
-    WARN("Unimplemented bytes > 32bits\n");
-    return FALSE;
-  }
-
-  f.l_start = dwFileOffsetLow;
-  f.l_len = nNumberOfBytesToUnlockLow;
-  f.l_whence = SEEK_SET;
-  f.l_pid = 0;
-  f.l_type = F_UNLCK;
-
-  if (!(file = FILE_GetFile(hFile,0,NULL))) return FALSE;
-
-  DOS_RemoveLock(file, &f);	/* ok if fails - may be another wine */
-
-  /* FIXME: Unix locking commented out for now, doesn't work with Excel */
-#ifdef USE_UNIX_LOCKS
-  if (fcntl(file->unix_handle, F_SETLK, &f) == -1) {
-    FILE_SetDosError();
-    return FALSE;
-  }
-#endif
-  return TRUE;
-}
-#endif
 
 /**************************************************************************
  *           GetFileAttributesExW   (KERNEL32.@)
diff --git a/include/winbase.h b/include/winbase.h
index fce2e8ad31f..89a1e06169e 100644
--- a/include/winbase.h
+++ b/include/winbase.h
@@ -293,6 +293,8 @@ typedef struct _PROCESS_HEAP_ENTRY
 #define INVALID_SET_FILE_POINTER ((DWORD)-1)
 #define INVALID_FILE_ATTRIBUTES  ((DWORD)-1)
 
+#define LOCKFILE_FAIL_IMMEDIATELY   1
+#define LOCKFILE_EXCLUSIVE_LOCK     2
 
 #define TLS_OUT_OF_INDEXES ((DWORD)0xFFFFFFFF)
 
diff --git a/include/wine/server_protocol.h b/include/wine/server_protocol.h
index 5555f062f0b..931ae58737b 100644
--- a/include/wine/server_protocol.h
+++ b/include/wine/server_protocol.h
@@ -899,10 +899,14 @@ struct lock_file_request
     unsigned int offset_high;
     unsigned int count_low;
     unsigned int count_high;
+    int          shared;
+    int          wait;
 };
 struct lock_file_reply
 {
     struct reply_header __header;
+    obj_handle_t handle;
+    int          overlapped;
 };
 
 
@@ -3551,6 +3555,6 @@ union generic_reply
     struct get_next_hook_reply get_next_hook_reply;
 };
 
-#define SERVER_PROTOCOL_VERSION 99
+#define SERVER_PROTOCOL_VERSION 100
 
 #endif /* __WINE_WINE_SERVER_PROTOCOL_H */
diff --git a/server/fd.c b/server/fd.c
index dc6f1601763..af963465226 100644
--- a/server/fd.c
+++ b/server/fd.c
@@ -1,7 +1,7 @@
 /*
  * Server-side file descriptor management
  *
- * Copyright (C) 2003 Alexandre Julliard
+ * Copyright (C) 2000, 2003 Alexandre Julliard
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -22,7 +22,9 @@
 #include "config.h"
 
 #include <assert.h>
+#include <errno.h>
 #include <fcntl.h>
+#include <limits.h>
 #include <signal.h>
 #include <stdio.h>
 #include <string.h>
@@ -42,6 +44,11 @@
 #include "request.h"
 #include "console.h"
 
+/* Because of the stupid Posix locking semantics, we need to keep
+ * track of all file descriptors referencing a given file, and not
+ * close a single one until all the locks are gone (sigh).
+ */
+
 /* file descriptor object */
 
 /* closed_fd is used to keep track of the unix fd belonging to a closed fd object */
@@ -59,6 +66,7 @@ struct fd
     struct list          inode_entry; /* entry in inode fd list */
     struct closed_fd    *closed;      /* structure to store the unix fd at destroy time */
     struct object       *user;        /* object using this file descriptor */
+    struct list          locks;       /* list of locks on this fd */
     int                  unix_fd;     /* unix file descriptor */
     int                  poll_index;  /* index of fd in poll array */
 };
@@ -88,6 +96,7 @@ struct inode
     dev_t               dev;        /* device number */
     ino_t               ino;        /* inode number */
     struct list         open;       /* list of open file descriptors */
+    struct list         locks;      /* list of file locks */
     struct closed_fd   *closed;     /* list of file descriptors to close at destroy time */
 };
 
@@ -106,6 +115,42 @@ static const struct object_ops inode_ops =
     inode_destroy             /* destroy */
 };
 
+/* file lock object */
+
+struct file_lock
+{
+    struct object       obj;         /* object header */
+    struct fd          *fd;          /* fd owning this lock */
+    struct list         fd_entry;    /* entry in list of locks on a given fd */
+    struct list         inode_entry; /* entry in inode list of locks */
+    int                 shared;      /* shared lock? */
+    file_pos_t          start;       /* locked region is interval [start;end) */
+    file_pos_t          end;
+    struct process     *process;     /* process owning this lock */
+    struct list         proc_entry;  /* entry in list of locks owned by the process */
+};
+
+static void file_lock_dump( struct object *obj, int verbose );
+static int file_lock_signaled( struct object *obj, struct thread *thread );
+
+static const struct object_ops file_lock_ops =
+{
+    sizeof(struct file_lock),   /* size */
+    file_lock_dump,             /* dump */
+    add_queue,                  /* add_queue */
+    remove_queue,               /* remove_queue */
+    file_lock_signaled,         /* signaled */
+    no_satisfied,               /* satisfied */
+    no_get_fd,                  /* get_fd */
+    no_destroy                  /* destroy */
+};
+
+
+#define OFF_T_MAX       (~((file_pos_t)1 << (8*sizeof(off_t)-1)))
+#define FILE_POS_T_MAX  (~(file_pos_t)0)
+
+static file_pos_t max_unix_offset = OFF_T_MAX;
+
 #define DUMP_LONG_LONG(val) do { \
     if (sizeof(val) > sizeof(unsigned long) && (val) > ~0UL) \
         fprintf( stderr, "%lx%08lx", (unsigned long)((val) >> 32), (unsigned long)(val) ); \
@@ -368,6 +413,18 @@ void main_loop(void)
 
 static struct list inode_hash[HASH_SIZE];
 
+/* close all pending file descriptors in the closed list */
+static void inode_close_pending( struct inode *inode )
+{
+    while (inode->closed)
+    {
+        struct closed_fd *fd = inode->closed;
+        inode->closed = fd->next;
+        close( fd->fd );
+        free( fd );
+    }
+}
+
 
 static void inode_dump( struct object *obj, int verbose )
 {
@@ -383,16 +440,11 @@ static void inode_destroy( struct object *obj )
 {
     struct inode *inode = (struct inode *)obj;
 
-    assert( !list_head(&inode->open) );
+    assert( list_empty(&inode->open) );
+    assert( list_empty(&inode->locks) );
 
     list_remove( &inode->entry );
-    while (inode->closed)
-    {
-        struct closed_fd *fd = inode->closed;
-        inode->closed = fd->next;
-        close( fd->fd );
-        free( fd );
-    }
+    inode_close_pending( inode );
 }
 
 /* retrieve the inode object for a given fd, creating it if needed */
@@ -421,6 +473,7 @@ static struct inode *get_inode( dev_t dev, ino_t ino )
         inode->ino    = ino;
         inode->closed = NULL;
         list_init( &inode->open );
+        list_init( &inode->locks );
         list_add_head( &inode_hash[hash], &inode->entry );
     }
     return inode;
@@ -429,8 +482,315 @@ static struct inode *get_inode( dev_t dev, ino_t ino )
 /* add fd to the indoe list of file descriptors to close */
 static void inode_add_closed_fd( struct inode *inode, struct closed_fd *fd )
 {
-    fd->next = inode->closed;
-    inode->closed = fd;
+    if (!list_empty( &inode->locks ))
+    {
+        fd->next = inode->closed;
+        inode->closed = fd;
+    }
+    else  /* no locks on this inode, we can close the fd right away */
+    {
+        close( fd->fd );
+        free( fd );
+    }
+}
+
+
+/****************************************************************/
+/* file lock functions */
+
+static void file_lock_dump( struct object *obj, int verbose )
+{
+    struct file_lock *lock = (struct file_lock *)obj;
+    fprintf( stderr, "Lock %s fd=%p proc=%p start=",
+             lock->shared ? "shared" : "excl", lock->fd, lock->process );
+    DUMP_LONG_LONG( lock->start );
+    fprintf( stderr, " end=" );
+    DUMP_LONG_LONG( lock->end );
+    fprintf( stderr, "\n" );
+}
+
+static int file_lock_signaled( struct object *obj, struct thread *thread )
+{
+    struct file_lock *lock = (struct file_lock *)obj;
+    /* lock is signaled if it has lost its owner */
+    return !lock->process;
+}
+
+/* set (or remove) a Unix lock if possible for the given range */
+static int set_unix_lock( const struct fd *fd, file_pos_t start, file_pos_t end, int type )
+{
+    struct flock fl;
+
+    for (;;)
+    {
+        if (start == end) return 1;  /* can't set zero-byte lock */
+        if (start > max_unix_offset) return 1;  /* ignore it */
+        fl.l_type   = type;
+        fl.l_whence = SEEK_SET;
+        fl.l_start  = start;
+        if (!end || end > max_unix_offset) fl.l_len = 0;
+        else fl.l_len = end - start;
+        if (fcntl( fd->unix_fd, F_SETLK, &fl ) != -1) return 1;
+
+        switch(errno)
+        {
+        case EACCES:
+        case EAGAIN:
+            set_error( STATUS_FILE_LOCK_CONFLICT );
+            return 0;
+        case EOVERFLOW:
+            /* this can happen if off_t is 64-bit but the kernel only supports 32-bit */
+            /* in that case we shrink the limit and retry */
+            if (max_unix_offset > INT_MAX)
+            {
+                max_unix_offset = INT_MAX;
+                break;  /* retry */
+            }
+            /* fall through */
+        default:
+            file_set_error();
+            return 0;
+        }
+    }
+}
+
+/* check if interval [start;end) overlaps the lock */
+inline static int lock_overlaps( struct file_lock *lock, file_pos_t start, file_pos_t end )
+{
+    if (lock->end && start >= lock->end) return 0;
+    if (end && lock->start >= end) return 0;
+    return 1;
+}
+
+/* remove Unix locks for all bytes in the specified area that are no longer locked */
+static void remove_unix_locks( const struct fd *fd, file_pos_t start, file_pos_t end )
+{
+    struct hole
+    {
+        struct hole *next;
+        struct hole *prev;
+        file_pos_t   start;
+        file_pos_t   end;
+    } *first, *cur, *next, *buffer;
+
+    struct list *ptr;
+    int count = 0;
+
+    if (!fd->inode) return;
+    if (start == end || start > max_unix_offset) return;
+    if (!end || end > max_unix_offset) end = max_unix_offset + 1;
+
+    /* count the number of locks overlapping the specified area */
+
+    LIST_FOR_EACH( ptr, &fd->inode->locks )
+    {
+        struct file_lock *lock = LIST_ENTRY( ptr, struct file_lock, inode_entry );
+        if (lock->start == lock->end) continue;
+        if (lock_overlaps( lock, start, end )) count++;
+    }
+
+    if (!count)  /* no locks at all, we can unlock everything */
+    {
+        set_unix_lock( fd, start, end, F_UNLCK );
+        return;
+    }
+
+    /* allocate space for the list of holes */
+    /* max. number of holes is number of locks + 1 */
+
+    if (!(buffer = malloc( sizeof(*buffer) * (count+1) ))) return;
+    first = buffer;
+    first->next  = NULL;
+    first->prev  = NULL;
+    first->start = start;
+    first->end   = end;
+    next = first + 1;
+
+    /* build a sorted list of unlocked holes in the specified area */
+
+    LIST_FOR_EACH( ptr, &fd->inode->locks )
+    {
+        struct file_lock *lock = LIST_ENTRY( ptr, struct file_lock, inode_entry );
+        if (lock->start == lock->end) continue;
+        if (!lock_overlaps( lock, start, end )) continue;
+
+        /* go through all the holes touched by this lock */
+        for (cur = first; cur; cur = cur->next)
+        {
+            if (cur->end <= lock->start) continue; /* hole is before start of lock */
+            if (lock->end && cur->start >= lock->end) break;  /* hole is after end of lock */
+
+            /* now we know that lock is overlapping hole */
+
+            if (cur->start >= lock->start)  /* lock starts before hole, shrink from start */
+            {
+                cur->start = lock->end;
+                if (cur->start && cur->start < cur->end) break;  /* done with this lock */
+                /* now hole is empty, remove it */
+                if (cur->next) cur->next->prev = cur->prev;
+                if (cur->prev) cur->prev->next = cur->next;
+                else if (!(first = cur->next)) goto done;  /* no more holes at all */
+            }
+            else if (!lock->end || cur->end <= lock->end)  /* lock larger than hole, shrink from end */
+            {
+                cur->end = lock->start;
+                assert( cur->start < cur->end );
+            }
+            else  /* lock is in the middle of hole, split hole in two */
+            {
+                next->prev = cur;
+                next->next = cur->next;
+                cur->next = next;
+                next->start = lock->end;
+                next->end = cur->end;
+                cur->end = lock->start;
+                assert( next->start < next->end );
+                assert( cur->end < next->start );
+                next++;
+                break;  /* done with this lock */
+            }
+        }
+    }
+
+    /* clear Unix locks for all the holes */
+
+    for (cur = first; cur; cur = cur->next)
+        set_unix_lock( fd, cur->start, cur->end, F_UNLCK );
+
+ done:
+    free( buffer );
+}
+
+/* create a new lock on a fd */
+static struct file_lock *add_lock( struct fd *fd, int shared, file_pos_t start, file_pos_t end )
+{
+    struct file_lock *lock;
+
+    if (!fd->inode)  /* not a regular file */
+    {
+        set_error( STATUS_INVALID_HANDLE );
+        return NULL;
+    }
+
+    if (!(lock = alloc_object( &file_lock_ops ))) return NULL;
+    lock->shared  = shared;
+    lock->start   = start;
+    lock->end     = end;
+    lock->fd      = fd;
+    lock->process = current->process;
+
+    /* now try to set a Unix lock */
+    if (!set_unix_lock( lock->fd, lock->start, lock->end, lock->shared ? F_RDLCK : F_WRLCK ))
+    {
+        release_object( lock );
+        return NULL;
+    }
+    list_add_head( &fd->locks, &lock->fd_entry );
+    list_add_head( &fd->inode->locks, &lock->inode_entry );
+    list_add_head( &lock->process->locks, &lock->proc_entry );
+    return lock;
+}
+
+/* remove an existing lock */
+static void remove_lock( struct file_lock *lock, int remove_unix )
+{
+    struct inode *inode = lock->fd->inode;
+
+    list_remove( &lock->fd_entry );
+    list_remove( &lock->inode_entry );
+    list_remove( &lock->proc_entry );
+    if (remove_unix) remove_unix_locks( lock->fd, lock->start, lock->end );
+    if (list_empty( &inode->locks )) inode_close_pending( inode );
+    lock->process = NULL;
+    wake_up( &lock->obj, 0 );
+    release_object( lock );
+}
+
+/* remove all locks owned by a given process */
+void remove_process_locks( struct process *process )
+{
+    struct list *ptr;
+
+    while ((ptr = list_head( &process->locks )))
+    {
+        struct file_lock *lock = LIST_ENTRY( ptr, struct file_lock, proc_entry );
+        remove_lock( lock, 1 );  /* this removes it from the list */
+    }
+}
+
+/* remove all locks on a given fd */
+static void remove_fd_locks( struct fd *fd )
+{
+    file_pos_t start = FILE_POS_T_MAX, end = 0;
+    struct list *ptr;
+
+    while ((ptr = list_head( &fd->locks )))
+    {
+        struct file_lock *lock = LIST_ENTRY( ptr, struct file_lock, fd_entry );
+        if (lock->start < start) start = lock->start;
+        if (!lock->end || lock->end > end) end = lock->end - 1;
+        remove_lock( lock, 0 );
+    }
+    if (start < end) remove_unix_locks( fd, start, end + 1 );
+}
+
+/* add a lock on an fd */
+/* returns handle to wait on */
+obj_handle_t lock_fd( struct fd *fd, file_pos_t start, file_pos_t count, int shared, int wait )
+{
+    struct list *ptr;
+    file_pos_t end = start + count;
+
+    /* don't allow wrapping locks */
+    if (end && end < start)
+    {
+        set_error( STATUS_INVALID_PARAMETER );
+        return 0;
+    }
+
+    /* check if another lock on that file overlaps the area */
+    LIST_FOR_EACH( ptr, &fd->inode->locks )
+    {
+        struct file_lock *lock = LIST_ENTRY( ptr, struct file_lock, inode_entry );
+        if (!lock_overlaps( lock, start, end )) continue;
+        if (lock->shared && shared) continue;
+        /* found one */
+        if (!wait)
+        {
+            set_error( STATUS_FILE_LOCK_CONFLICT );
+            return 0;
+        }
+        set_error( STATUS_PENDING );
+        return alloc_handle( current->process, lock, SYNCHRONIZE, 0 );
+    }
+
+    /* not found, add it */
+    if (add_lock( fd, shared, start, end )) return 0;
+    if (get_error() == STATUS_FILE_LOCK_CONFLICT)
+    {
+        /* Unix lock conflict -> tell client to wait and retry */
+        if (wait) set_error( STATUS_PENDING );
+    }
+    return 0;
+}
+
+/* remove a lock on an fd */
+void unlock_fd( struct fd *fd, file_pos_t start, file_pos_t count )
+{
+    struct list *ptr;
+    file_pos_t end = start + count;
+
+    /* find an existing lock with the exact same parameters */
+    LIST_FOR_EACH( ptr, &fd->locks )
+    {
+        struct file_lock *lock = LIST_ENTRY( ptr, struct file_lock, fd_entry );
+        if ((lock->start == start) && (lock->end == end))
+        {
+            remove_lock( lock, 1 );
+            return;
+        }
+    }
+    set_error( STATUS_FILE_LOCK_CONFLICT );
 }
 
 
@@ -447,6 +807,7 @@ static void fd_destroy( struct object *obj )
 {
     struct fd *fd = (struct fd *)obj;
 
+    remove_fd_locks( fd );
     list_remove( &fd->inode_entry );
     if (fd->poll_index != -1) remove_poll_user( fd, fd->poll_index );
     if (fd->inode)
@@ -492,6 +853,7 @@ struct fd *alloc_fd( const struct fd_ops *fd_user_ops, struct object *user )
     fd->unix_fd    = -1;
     fd->poll_index = -1;
     list_init( &fd->inode_entry );
+    list_init( &fd->locks );
 
     if ((fd->poll_index = add_poll_user( fd )) == -1)
     {
diff --git a/server/file.c b/server/file.c
index ba853e9fe2d..c14c4ee23b2 100644
--- a/server/file.c
+++ b/server/file.c
@@ -453,6 +453,7 @@ void file_set_error(void)
     case ESPIPE:    set_error( 0xc0010000 | ERROR_SEEK /* FIXME */ ); break;
     case ENOTEMPTY: set_error( STATUS_DIRECTORY_NOT_EMPTY ); break;
     case EIO:       set_error( STATUS_ACCESS_VIOLATION ); break;
+    case EOVERFLOW: set_error( STATUS_INVALID_PARAMETER ); break;
     default:        perror("file_set_error"); set_error( ERROR_UNKNOWN /* FIXME */ ); break;
     }
 }
@@ -581,20 +582,6 @@ static int set_file_time( obj_handle_t handle, time_t access_time, time_t write_
     return 0;
 }
 
-static int file_lock( struct file *file, int offset_high, int offset_low,
-                      int count_high, int count_low )
-{
-    /* FIXME: implement this */
-    return 1;
-}
-
-static int file_unlock( struct file *file, int offset_high, int offset_low,
-                        int count_high, int count_low )
-{
-    /* FIXME: implement this */
-    return 1;
-}
-
 /* create a file */
 DECL_HANDLER(create_file)
 {
@@ -661,11 +648,13 @@ DECL_HANDLER(set_file_time)
 DECL_HANDLER(lock_file)
 {
     struct file *file;
+    file_pos_t offset = ((file_pos_t)req->offset_high << 32) | req->offset_low;
+    file_pos_t count = ((file_pos_t)req->count_high << 32) | req->count_low;
 
     if ((file = get_file_obj( current->process, req->handle, 0 )))
     {
-        file_lock( file, req->offset_high, req->offset_low,
-                   req->count_high, req->count_low );
+        reply->handle = lock_fd( file->fd, offset, count, req->shared, req->wait );
+        reply->overlapped = (file->flags & FILE_FLAG_OVERLAPPED) != 0;
         release_object( file );
     }
 }
@@ -674,11 +663,12 @@ DECL_HANDLER(lock_file)
 DECL_HANDLER(unlock_file)
 {
     struct file *file;
+    file_pos_t offset = ((file_pos_t)req->offset_high << 32) | req->offset_low;
+    file_pos_t count = ((file_pos_t)req->count_high << 32) | req->count_low;
 
     if ((file = get_file_obj( current->process, req->handle, 0 )))
     {
-        file_unlock( file, req->offset_high, req->offset_low,
-                     req->count_high, req->count_low );
+        unlock_fd( file->fd, offset, count );
         release_object( file );
     }
 }
diff --git a/server/file.h b/server/file.h
index ff59f37de73..88e2be99af8 100644
--- a/server/file.h
+++ b/server/file.h
@@ -25,6 +25,8 @@
 
 struct fd;
 
+typedef unsigned __int64 file_pos_t;
+
 /* operations valid on file descriptor objects */
 struct fd_ops
 {
@@ -51,6 +53,8 @@ extern int get_unix_fd( struct fd *fd );
 extern void fd_poll_event( struct fd *fd, int event );
 extern int check_fd_events( struct fd *fd, int events );
 extern void set_fd_events( struct fd *fd, int events );
+extern obj_handle_t lock_fd( struct fd *fd, file_pos_t offset, file_pos_t count, int shared, int wait );
+extern void unlock_fd( struct fd *fd, file_pos_t offset, file_pos_t count );
 
 extern int default_fd_add_queue( struct object *obj, struct wait_queue_entry *entry );
 extern void default_fd_remove_queue( struct object *obj, struct wait_queue_entry *entry );
diff --git a/server/list.h b/server/list.h
index fcf687e3e66..993aaaf2a11 100644
--- a/server/list.h
+++ b/server/list.h
@@ -80,6 +80,12 @@ inline static struct list *list_tail( struct list *list )
     return list_prev( list, list );
 }
 
+/* check if a list is empty */
+inline static int list_empty( struct list *list )
+{
+    return list->next == list;
+}
+
 /* initialize a list */
 inline static void list_init( struct list *list )
 {
diff --git a/server/process.c b/server/process.c
index f26b62a47aa..0617bb50b31 100644
--- a/server/process.c
+++ b/server/process.c
@@ -296,6 +296,7 @@ struct thread *create_process( int fd )
     process->exe.namelen     = 0;
     process->exe.filename    = NULL;
     process->group_id        = 0;
+    list_init( &process->locks );
 
     gettimeofday( &process->start_time, NULL );
     if ((process->next = first_process) != NULL) process->next->prev = process;
diff --git a/server/process.h b/server/process.h
index cd65153e0ae..b79982a7153 100644
--- a/server/process.h
+++ b/server/process.h
@@ -67,6 +67,7 @@ struct process
     int                  affinity;        /* process affinity mask */
     int                  suspend;         /* global process suspend count */
     int                  create_flags;    /* process creation flags */
+    struct list          locks;           /* list of file locks owned by the process */
     struct console_input*console;         /* console input */
     enum startup_state   startup_state;   /* startup state */
     struct startup_info *startup_info;    /* startup info while init is in progress */
diff --git a/server/protocol.def b/server/protocol.def
index 805ad8b6fdd..f1a4edb0b0c 100644
--- a/server/protocol.def
+++ b/server/protocol.def
@@ -681,6 +681,11 @@ enum fd_type
     unsigned int offset_high;   /* offset of start of lock */
     unsigned int count_low;     /* count of bytes to lock */
     unsigned int count_high;    /* count of bytes to lock */
+    int          shared;        /* shared or exclusive lock? */
+    int          wait;          /* do we want to wait? */
+@REPLY
+    obj_handle_t handle;        /* handle to wait on */
+    int          overlapped;    /* is it an overlapped I/O handle? */
 @END
 
 
diff --git a/server/trace.c b/server/trace.c
index 1e09f62f102..b9c6f1c5c6c 100644
--- a/server/trace.c
+++ b/server/trace.c
@@ -889,7 +889,15 @@ static void dump_lock_file_request( const struct lock_file_request *req )
     fprintf( stderr, " offset_low=%08x,", req->offset_low );
     fprintf( stderr, " offset_high=%08x,", req->offset_high );
     fprintf( stderr, " count_low=%08x,", req->count_low );
-    fprintf( stderr, " count_high=%08x", req->count_high );
+    fprintf( stderr, " count_high=%08x,", req->count_high );
+    fprintf( stderr, " shared=%d,", req->shared );
+    fprintf( stderr, " wait=%d", req->wait );
+}
+
+static void dump_lock_file_reply( const struct lock_file_reply *req )
+{
+    fprintf( stderr, " handle=%p,", req->handle );
+    fprintf( stderr, " overlapped=%d", req->overlapped );
 }
 
 static void dump_unlock_file_request( const struct unlock_file_request *req )
@@ -2632,7 +2640,7 @@ static const dump_func reply_dumpers[REQ_NB_REQUESTS] = {
     (dump_func)0,
     (dump_func)0,
     (dump_func)dump_get_file_info_reply,
-    (dump_func)0,
+    (dump_func)dump_lock_file_reply,
     (dump_func)0,
     (dump_func)dump_create_pipe_reply,
     (dump_func)dump_create_socket_reply,