sqlite3_free(p->apRegion);
    if( p->h>=0 ) close(p->h);
    p->pInode->pShmNode = 0;
    sqlite3_free(p);
  }
}

/* Forward reference */
static const char *unixTempFileDir(int);

/*
** Open a shared-memory area.  This particular implementation uses
** mmapped files.
**
** zName is a filename used to identify the shared-memory area.  The
** implementation does not (and perhaps should not) use this name
** directly, but rather use it as a template for finding an appropriate
** name for the shared-memory storage.  In this implementation, the
** string "-index" is appended to zName and used as the name of the
** mmapped file.


**
** When opening a new shared-memory file, if no other instances of that
** file are currently open, in this process or in other processes, then
** the file must be truncated to zero length or have its header cleared.
*/
static int unixShmOpen(
  sqlite3_file *fd      /* The file descriptor of the associated database */
){
  struct unixShm *p = 0;             /* The connection to be opened */
  struct unixShmNode *pShmNode = 0;  /* The underlying mmapped file */
  int rc;                            /* Result code */
  struct unixFile *pDbFd;            /* Underlying database file */
  unixInodeInfo *pInode;             /* The inode of fd */
  const char *zTempDir;              /* Directory for temporary files */
  int nTempDir;                      /* Size of the zTempDir string */

  /* Allocate space for the new sqlite3_shm object.
  */
  p = sqlite3_malloc( sizeof(*p) );
  if( p==0 ) return SQLITE_NOMEM;
  memset(p, 0, sizeof(*p));
  pDbFd = (struct unixFile*)fd;
................................................................................
  /* Check to see if a unixShmNode object already exists.  Reuse an existing
  ** one if present.  Create a new one if necessary.
  */
  unixEnterMutex();
  pInode = pDbFd->pInode;
  pShmNode = pInode->pShmNode;
  if( pShmNode==0 ){
    zTempDir = unixTempFileDir(1);
    if( zTempDir==0 ){
      unixLeaveMutex();
      sqlite3_free(p);
      return SQLITE_CANTOPEN_NOTEMPDIR;
    }
    nTempDir = strlen(zTempDir);
    pShmNode = sqlite3_malloc( sizeof(*pShmNode) + nTempDir + 50 );
    if( pShmNode==0 ){
      rc = SQLITE_NOMEM;
      goto shm_open_err;
    }
    memset(pShmNode, 0, sizeof(*pShmNode));
    pShmNode->zFilename = (char*)&pShmNode[1];
    sqlite3_snprintf(nTempDir+50, pShmNode->zFilename,
                     "%s/sqlite-wi-%x-%x", zTempDir,
                     (u32)pInode->fileId.dev, (u32)pInode->fileId.ino);
    pShmNode->h = -1;
    pDbFd->pInode->pShmNode = pShmNode;
    pShmNode->pInode = pDbFd->pInode;
    pShmNode->mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
    if( pShmNode->mutex==0 ){
      rc = SQLITE_NOMEM;
      goto shm_open_err;
    }

    pShmNode->h = open(pShmNode->zFilename, O_RDWR|O_CREAT, 0664);
    if( pShmNode->h<0 ){
      rc = SQLITE_CANTOPEN_BKPT;
      goto shm_open_err;
    }

    /* Check to see if another process is holding the dead-man switch.
    ** If not, truncate the file to zero length. 
................................................................................
  return (fd>=0?SQLITE_OK:SQLITE_CANTOPEN_BKPT);
}

/*
** Return the name of a directory in which to put temporary files.
** If no suitable temporary file directory can be found, return NULL.
*/
static const char *unixTempFileDir(int allowShm){
  static const char *azDirs[] = {
     0,
     0,
     "/var/tmp",
     "/usr/tmp",
     "/tmp",
     0        /* List terminator */
................................................................................
  };
  unsigned int i;
  struct stat buf;
  const char *zDir = 0;

  azDirs[0] = sqlite3_temp_directory;
  if( !azDirs[1] ) azDirs[1] = getenv("TMPDIR");
  
  if( allowShm ){
    zDir = "/dev/shm";
    i = 2;  /* Skip the app-defined temp locations for shared-memory */
  }else{
    zDir = azDirs[0];
    i = 1;
  }
  for(; i<sizeof(azDirs)/sizeof(azDirs[0]); zDir=azDirs[i++]){
    if( zDir==0 ) continue;
    if( stat(zDir, &buf) ) continue;
    if( !S_ISDIR(buf.st_mode) ) continue;
    if( !allowShm && access(zDir, 07) ) continue;
    break;
  }
  return zDir;
}

/*
** Create a temporary file name in zBuf.  zBuf must be allocated
................................................................................

  /* It's odd to simulate an io-error here, but really this is just
  ** using the io-error infrastructure to test that SQLite handles this
  ** function failing. 
  */
  SimulateIOError( return SQLITE_IOERR );

  zDir = unixTempFileDir(0);
  if( zDir==0 ) zDir = ".";

  /* Check that the output buffer is large enough for the temporary file 
  ** name. If it is not, return SQLITE_ERROR.
  */
  if( (strlen(zDir) + strlen(SQLITE_TEMP_FILE_PREFIX) + 17) >= (size_t)nBuf ){
    return SQLITE_ERROR;

    sqlite3_free(p->apRegion);
    if( p->h>=0 ) close(p->h);
    p->pInode->pShmNode = 0;
    sqlite3_free(p);
  }
}

/*
** Open a shared-memory area associated with open database file fd.  
** This particular implementation uses mmapped files.
**
** The file used to implement shared-memory is in the same directory
** as the open database file and has the same name as the open database
** file with the "-shm" suffix added.  For example, if the database file
** is "/home/user1/config.db" then the file that is created and mmapped
** for shared memory will be called "/home/user1/config.db-shm".  We
** experimented with using files in /dev/tmp or an some other tmpfs mount.
** But if a file in a different directory from the database file is used,
** then differing access permissions or a chroot() might cause two different 
** processes on the same database to end up using different files for 
** shared memory - meaning that their memory would not really be shared - 
** resulting in database corruption.
**
** When opening a new shared-memory file, if no other instances of that
** file are currently open, in this process or in other processes, then
** the file must be truncated to zero length or have its header cleared.
*/
static int unixShmOpen(
  sqlite3_file *fd      /* The file descriptor of the associated database */
){
  struct unixShm *p = 0;             /* The connection to be opened */
  struct unixShmNode *pShmNode = 0;  /* The underlying mmapped file */
  int rc;                            /* Result code */
  struct unixFile *pDbFd;            /* Underlying database file */
  unixInodeInfo *pInode;             /* The inode of fd */
  char *zShmFilename;                /* Name of the file used for SHM */
  int nShmFilename;                  /* Size of the SHM filename in bytes */

  /* Allocate space for the new sqlite3_shm object.
  */
  p = sqlite3_malloc( sizeof(*p) );
  if( p==0 ) return SQLITE_NOMEM;
  memset(p, 0, sizeof(*p));
  pDbFd = (struct unixFile*)fd;
................................................................................
  /* Check to see if a unixShmNode object already exists.  Reuse an existing
  ** one if present.  Create a new one if necessary.
  */
  unixEnterMutex();
  pInode = pDbFd->pInode;
  pShmNode = pInode->pShmNode;
  if( pShmNode==0 ){
    nShmFilename = 5 + (int)strlen(pDbFd->zPath);






    pShmNode = sqlite3_malloc( sizeof(*pShmNode) + nShmFilename );
    if( pShmNode==0 ){
      rc = SQLITE_NOMEM;
      goto shm_open_err;
    }
    memset(pShmNode, 0, sizeof(*pShmNode));
    zShmFilename = pShmNode->zFilename = (char*)&pShmNode[1];
    sqlite3_snprintf(nShmFilename, zShmFilename, "%s-shm", pDbFd->zPath);


    pShmNode->h = -1;
    pDbFd->pInode->pShmNode = pShmNode;
    pShmNode->pInode = pDbFd->pInode;
    pShmNode->mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
    if( pShmNode->mutex==0 ){
      rc = SQLITE_NOMEM;
      goto shm_open_err;
    }

    pShmNode->h = open(zShmFilename, O_RDWR|O_CREAT, 0664);
    if( pShmNode->h<0 ){
      rc = SQLITE_CANTOPEN_BKPT;
      goto shm_open_err;
    }

    /* Check to see if another process is holding the dead-man switch.
    ** If not, truncate the file to zero length. 
................................................................................
  return (fd>=0?SQLITE_OK:SQLITE_CANTOPEN_BKPT);
}

/*
** Return the name of a directory in which to put temporary files.
** If no suitable temporary file directory can be found, return NULL.
*/
static const char *unixTempFileDir(void){
  static const char *azDirs[] = {
     0,
     0,
     "/var/tmp",
     "/usr/tmp",
     "/tmp",
     0        /* List terminator */
................................................................................
  };
  unsigned int i;
  struct stat buf;
  const char *zDir = 0;

  azDirs[0] = sqlite3_temp_directory;
  if( !azDirs[1] ) azDirs[1] = getenv("TMPDIR");








  for(i==0; i<sizeof(azDirs)/sizeof(azDirs[0]); zDir=azDirs[i++]){
    if( zDir==0 ) continue;
    if( stat(zDir, &buf) ) continue;
    if( !S_ISDIR(buf.st_mode) ) continue;
    if( access(zDir, 07) ) continue;
    break;
  }
  return zDir;
}

/*
** Create a temporary file name in zBuf.  zBuf must be allocated
................................................................................

  /* It's odd to simulate an io-error here, but really this is just
  ** using the io-error infrastructure to test that SQLite handles this
  ** function failing. 
  */
  SimulateIOError( return SQLITE_IOERR );

  zDir = unixTempFileDir();
  if( zDir==0 ) zDir = ".";

  /* Check that the output buffer is large enough for the temporary file 
  ** name. If it is not, return SQLITE_ERROR.
  */
  if( (strlen(zDir) + strlen(SQLITE_TEMP_FILE_PREFIX) + 17) >= (size_t)nBuf ){
    return SQLITE_ERROR;