SQLite

  { "unlink",       (sqlite3_syscall_ptr)unlink,           0 },
#define osUnlink    ((int(*)(const char*))aSyscall[16].pCurrent)

  { "openDirectory",    (sqlite3_syscall_ptr)openDirectory,      0 },
#define osOpenDirectory ((int(*)(const char*,int*))aSyscall[17].pCurrent)

  { "mkdir",        (sqlite3_syscall_ptr)mkdir,           0 },
#define osMkdir     ((int(*)(const char*,mode_t))aSyscall[18].pCurrent)

  { "rmdir",        (sqlite3_syscall_ptr)rmdir,           0 },
#define osRmdir     ((int(*)(const char*))aSyscall[19].pCurrent)

}; /* End of the overrideable system calls */

/*
** This is the xSetSystemCall() method of sqlite3_vfs for all of the
** "unix" VFSes.  Return SQLITE_OK opon successfully updating the
** system call pointer, or SQLITE_NOTFOUND if there is no configurable
** system call named zName.

/******************* End of the no-op lock implementation *********************
******************************************************************************/

/******************************************************************************
************************* Begin dot-file Locking ******************************
**
** The dotfile locking implementation uses the existance of separate lock
** files (really a directory) to control access to the database.  This works
** on just about every filesystem imaginable.  But there are serious downsides:
**
**    (1)  There is zero concurrency.  A single reader blocks all other
**         connections from reading or writing the database.
**
**    (2)  An application crash or power loss can leave stale lock files
**         sitting around that need to be cleared manually.
**
** Nevertheless, a dotlock is an appropriate locking mode for use if no
** other locking strategy is available.
**
** Dotfile locking works by creating a subdirectory in the same directory as
** the database and with the same name but with a ".lock" extension added.
** The existance of a lock directory implies an EXCLUSIVE lock.  All other
** lock types (SHARED, RESERVED, PENDING) are mapped into EXCLUSIVE.
*/

/*
** The file suffix added to the data base filename in order to create the
** lock directory.
*/
#define DOTLOCK_SUFFIX ".lock"

/*
** This routine checks if there is a RESERVED lock held on the specified
** file by this or any other process. If such a lock is held, set *pResOut
** to a non-zero value otherwise *pResOut is set to zero.  The return value

** routine to lower a locking level.
**
** With dotfile locking, we really only support state (4): EXCLUSIVE.
** But we track the other locking levels internally.
*/
static int dotlockLock(sqlite3_file *id, int eFileLock) {
  unixFile *pFile = (unixFile*)id;

  char *zLockFile = (char *)pFile->lockingContext;
  int rc = SQLITE_OK;


  /* If we have any lock, then the lock file already exists.  All we have
  ** to do is adjust our internal record of the lock level.
  */
  if( pFile->eFileLock > NO_LOCK ){
    pFile->eFileLock = eFileLock;
    /* Always update the timestamp on the old file */
#ifdef HAVE_UTIME
    utime(zLockFile, NULL);
#else
    utimes(zLockFile, NULL);
#endif
    return SQLITE_OK;
  }
  
  /* grab an exclusive lock */
  rc = osMkdir(zLockFile, 0777);
  if( rc<0 ){
    /* failed to open/create the lock directory */
    int tErrno = errno;
    if( EEXIST == tErrno ){
      rc = SQLITE_BUSY;
    } else {
      rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK);
      if( IS_LOCK_ERROR(rc) ){
        pFile->lastErrno = tErrno;
      }
    }
    return rc;
  } 

  
  /* got it, set the type and return ok */
  pFile->eFileLock = eFileLock;
  return rc;
}

/*
** Lower the locking level on file descriptor pFile to eFileLock.  eFileLock
** must be either NO_LOCK or SHARED_LOCK.
**
** If the locking level of the file descriptor is already at or below
** the requested locking level, this routine is a no-op.
**
** When the locking level reaches NO_LOCK, delete the lock file.
*/
static int dotlockUnlock(sqlite3_file *id, int eFileLock) {
  unixFile *pFile = (unixFile*)id;
  char *zLockFile = (char *)pFile->lockingContext;
  int rc;

  assert( pFile );
  OSTRACE(("UNLOCK  %d %d was %d pid=%d (dotlock)\n", pFile->h, eFileLock,
	   pFile->eFileLock, getpid()));
  assert( eFileLock<=SHARED_LOCK );
  
  /* no-op if possible */

  if( eFileLock==SHARED_LOCK ){
    pFile->eFileLock = SHARED_LOCK;
    return SQLITE_OK;
  }
  
  /* To fully unlock the database, delete the lock file */
  assert( eFileLock==NO_LOCK );
  rc = osRmdir(zLockFile);
  if( rc<0 && errno==ENOTDIR ) rc = osUnlink(zLockFile);
  if( rc<0 ){
    int rc = 0;
    int tErrno = errno;
    if( ENOENT != tErrno ){
      rc = SQLITE_IOERR_UNLOCK;
    }
    if( IS_LOCK_ERROR(rc) ){
      pFile->lastErrno = tErrno;

  buf[0] = lockPath[0];
  for( i=1; i<len; i++ ){
    if( lockPath[i] == '/' && (i - start > 0) ){
      /* only mkdir if leaf dir != "." or "/" or ".." */
      if( i-start>2 || (i-start==1 && buf[start] != '.' && buf[start] != '/') 
         || (i-start==2 && buf[start] != '.' && buf[start+1] != '.') ){
        buf[i]='\0';
        if( osMkdir(buf, SQLITE_DEFAULT_PROXYDIR_PERMISSIONS) ){
          int err=errno;
          if( err!=EEXIST ) {
            OSTRACE(("CREATELOCKPATH  FAILED creating %s, "
                     "'%s' proxy lock path=%s pid=%d\n",
                     buf, strerror(err), lockPath, getpid()));
            return err;
          }

    UNIXVFS("unix-proxy",    proxyIoFinder ),
#endif
  };
  unsigned int i;          /* Loop counter */

  /* Double-check that the aSyscall[] array has been constructed
  ** correctly.  See ticket [bb3a86e890c8e96ab] */
  assert( ArraySize(aSyscall)==20 );

  /* Register all VFSes defined in the aVfs[] array */
  for(i=0; i<(sizeof(aVfs)/sizeof(sqlite3_vfs)); i++){
    sqlite3_vfs_register(&aVfs[i], i==0);
  }
  return SQLITE_OK; 
}

#-------------------------------------------------------------------------
# Tests for the xNextSystemCall method.
#
foreach s {
    open close access getcwd stat fstat ftruncate
    fcntl read pread write pwrite fchmod fallocate
    pread64 pwrite64 unlink openDirectory mkdir rmdir
} {
  if {[test_syscall exists $s]} {lappend syscall_list $s}
}
do_test 3.1 { lsort [test_syscall list] } [lsort $syscall_list]

#-------------------------------------------------------------------------
# This test verifies that if a call to open() fails and errno is set to