uefidevicepathlib.c

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  if (DevicePathInstance == NULL) {
    return NULL;
  }

  SrcSize       = GetDevicePathSize (DevicePath);
  InstanceSize  = GetDevicePathSize (DevicePathInstance);

  NewDevicePath = AllocatePool (SrcSize + InstanceSize);
  if (NewDevicePath != NULL) {
    
    TempDevicePath = CopyMem (NewDevicePath, DevicePath, SrcSize);;
 
    while (!IsDevicePathEnd (TempDevicePath)) {
      TempDevicePath = NextDevicePathNode (TempDevicePath);
    }
    
    TempDevicePath->SubType  = END_INSTANCE_DEVICE_PATH_SUBTYPE;
    TempDevicePath           = NextDevicePathNode (TempDevicePath);
    CopyMem (TempDevicePath, DevicePathInstance, InstanceSize);
  }

  return NewDevicePath;
}

/**
  Creates a copy of the current device path instance and returns a pointer to the next device path
  instance.

  This function creates a copy of the current device path instance. It also updates DevicePath to
  point to the next device path instance in the device path (or NULL if no more) and updates Size
  to hold the size of the device path instance copy.
  If DevicePath is NULL, then NULL is returned.
  If there is not enough memory to allocate space for the new device path, then NULL is returned.  
  The memory is allocated from EFI boot services memory. It is the responsibility of the caller to
  free the memory allocated.
  If Size is NULL, then ASSERT().
 
  @param  DevicePath                 On input, this holds the pointer to the current device path
                                     instance. On output, this holds the pointer to the next device
                                     path instance or NULL if there are no more device path
                                     instances in the device path pointer to a device path data
                                     structure.
  @param  Size                       On output, this holds the size of the device path instance, in
                                     bytes or zero, if DevicePath is NULL.

  @return A pointer to the current device path instance.

**/
EFI_DEVICE_PATH_PROTOCOL *
EFIAPI
GlueGetNextDevicePathInstance (
  IN OUT EFI_DEVICE_PATH_PROTOCOL    **DevicePath,
  OUT UINTN                          *Size
  )
{
  EFI_DEVICE_PATH_PROTOCOL  *DevPath;
  EFI_DEVICE_PATH_PROTOCOL  *ReturnValue;
  UINT8                     Temp;

  ASSERT (Size != NULL);

  if (DevicePath == NULL || *DevicePath == NULL) {
    *Size = 0;
    return NULL;
  }

  //
  // Find the end of the device path instance
  //
  DevPath = *DevicePath;
  while (!IsDevicePathEndType (DevPath)) {
    DevPath = NextDevicePathNode (DevPath);
  }

  //
  // Compute the size of the device path instance
  //
  *Size = ((UINTN) DevPath - (UINTN) (*DevicePath)) + sizeof (EFI_DEVICE_PATH_PROTOCOL);
 
  //
  // Make a copy and return the device path instance
  //
  Temp              = DevPath->SubType;
  DevPath->SubType  = END_ENTIRE_DEVICE_PATH_SUBTYPE;
  ReturnValue       = DuplicateDevicePath (*DevicePath);
  DevPath->SubType  = Temp;

  //
  // If DevPath is the end of an entire device path, then another instance
  // does not follow, so *DevicePath is set to NULL.
  //
  if (DevicePathSubType (DevPath) == END_ENTIRE_DEVICE_PATH_SUBTYPE) {
    *DevicePath = NULL;
  } else {
    *DevicePath = NextDevicePathNode (DevPath);
  }

  return ReturnValue;
}

/**
  Creates a copy of the current device path instance and returns a pointer to the next device path
  instance.

  This function creates a new device node in a newly allocated buffer of size NodeLength and
  initializes the device path node header with NodeType and NodeSubType.  The new device path node
  is returned.
  If NodeLength is smaller than a device path header, then NULL is returned.  
  If there is not enough memory to allocate space for the new device path, then NULL is returned.  
  The memory is allocated from EFI boot services memory. It is the responsibility of the caller to
  free the memory allocated.

  @param  NodeType                   The device node type for the new device node.
  @param  NodeSubType                The device node sub-type for the new device node.
  @param  NodeLength                 The length of the new device node.

  @return The new device path.

**/
EFI_DEVICE_PATH_PROTOCOL *
EFIAPI
CreateDeviceNode (
  IN UINT8                           NodeType,
  IN UINT8                           NodeSubType,
  IN UINT16                          NodeLength
  )
{
  EFI_DEVICE_PATH_PROTOCOL      *DevicePath;

  if (NodeLength < sizeof (EFI_DEVICE_PATH_PROTOCOL)) {
    //
    // NodeLength is less than the size of the header.
    //
    return NULL;
  }
 
  DevicePath = AllocatePool (NodeLength);
  if (DevicePath != NULL) {
     DevicePath->Type    = NodeType;
     DevicePath->SubType = NodeSubType;
     SetDevicePathNodeLength (DevicePath, NodeLength);
  }

  return DevicePath;
}

/**
  Determines if a device path is single or multi-instance.

  This function returns TRUE if the device path specified by DevicePath is multi-instance.
  Otherwise, FALSE is returned.  If DevicePath is NULL, then FALSE is returned.

  @param  DevicePath                 A pointer to a device path data structure.

  @retval  TRUE                      DevicePath is multi-instance.
  @retval  FALSE                     DevicePath is not multi-instance or DevicePath is NULL.

**/
BOOLEAN
EFIAPI
GlueIsDevicePathMultiInstance (
  IN CONST EFI_DEVICE_PATH_PROTOCOL  *DevicePath
  )
{
  CONST EFI_DEVICE_PATH_PROTOCOL     *Node;

  if (DevicePath == NULL) {
    return FALSE;
  }

  Node = DevicePath;
  while (!EfiIsDevicePathEnd (Node)) {
    if (EfiIsDevicePathEndInstance (Node)) {
      return TRUE;
    }

    Node = EfiNextDevicePathNode (Node);
  }

  return FALSE;
}


/**
  Retrieves the device path protocol from a handle.

  This function returns the device path protocol from the handle specified by Handle.  If Handle is
  NULL or Handle does not contain a device path protocol, then NULL is returned.
 
  @param  Handle                     The handle from which to retrieve the device path protocol.

  @return The device path protocol from the handle specified by Handle.

**/
EFI_DEVICE_PATH_PROTOCOL *
EFIAPI
GlueDevicePathFromHandle (
  IN EFI_HANDLE                      Handle
  )
{
  EFI_DEVICE_PATH_PROTOCOL  *DevicePath;
  EFI_STATUS                Status;

  Status = gBS->HandleProtocol (
                  Handle,
                  &gEfiDevicePathProtocolGuid,
                  (VOID *) &DevicePath
                  );
  if (EFI_ERROR (Status)) {
    DevicePath = NULL;
  }
  return DevicePath;
}

/**
  Allocates a device path for a file and appends it to an existing device path.

  If Device is a valid device handle that contains a device path protocol, then a device path for
  the file specified by FileName  is allocated and appended to the device path associated with the
  handle Device.  The allocated device path is returned.  If Device is NULL or Device is a handle
  that does not support the device path protocol, then a device path containing a single device
  path node for the file specified by FileName is allocated and returned.
  If FileName is NULL, then ASSERT().

  @param  Device                     A pointer to a device handle.  This parameter is optional and
                                     may be NULL.
  @param  FileName                   A pointer to a Null-terminated Unicode string.

  @return The allocated device path.

**/
EFI_DEVICE_PATH_PROTOCOL *
EFIAPI
GlueFileDevicePath (
  IN EFI_HANDLE                      Device,     OPTIONAL
  IN CONST CHAR16                    *FileName
  )
{
  UINTN                     Size;
  FILEPATH_DEVICE_PATH      *FilePath;
  EFI_DEVICE_PATH_PROTOCOL  *DevicePath;
  EFI_DEVICE_PATH_PROTOCOL  *FileDevicePath;

  DevicePath = NULL;

  Size = StrSize (FileName);
  FileDevicePath = AllocatePool (Size + SIZE_OF_FILEPATH_DEVICE_PATH + EFI_END_DEVICE_PATH_LENGTH);
  if (FileDevicePath != NULL) {
    FilePath = (FILEPATH_DEVICE_PATH *) FileDevicePath;
    FilePath->Header.Type    = MEDIA_DEVICE_PATH;
    FilePath->Header.SubType = MEDIA_FILEPATH_DP;
    CopyMem (&FilePath->PathName, FileName, Size);
    SetDevicePathNodeLength (&FilePath->Header, Size + SIZE_OF_FILEPATH_DEVICE_PATH);
    SetDevicePathEndNode (NextDevicePathNode (&FilePath->Header));

    if (Device != NULL) {
      DevicePath = DevicePathFromHandle (Device);
    }

    DevicePath = AppendDevicePath (DevicePath, FileDevicePath);
    FreePool (FileDevicePath);
  }

  return DevicePath;
}