CBFS Connect 2020 Python Edition

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on_set_valid_data_length Event

Fires when the OS needs to set a file's valid data length.


class CBFSSetValidDataLengthEventParams(object):
  def file_name() -> str: ...
  def valid_data_length() -> int: ...
  def handle_info() -> int: ...
  def file_context() -> int: ...
  def file_context(value) -> None: ...
  def handle_context() -> int: ...
  def handle_context(value) -> None: ...
  def result_code() -> int: ...
  def result_code(value) -> None: ...

# In class CBFS:
def on_set_valid_data_length() -> Callable[[CBFSSetValidDataLengthEventParams], None]: ...
def on_set_valid_data_length(event_hook: Callable[[CBFSSetValidDataLengthEventParams], None]) -> None: ...


This event fires when the OS needs to set the valid data length of the file specified by FileName. All files have three sizes associated with them:

Description Associated Event
File size The length, in bytes, of the file's contents. on_set_file_size
Allocation size The number of bytes allocated locally for the file. on_set_allocation_size
Valid data length The number of bytes that have been written to the file. on_set_valid_data_length

Typically, a file's valid data length is only explicitly changed when a process wishes to quickly allocate large amounts of storage space. In such cases, the on_set_file_size event will fire first to set the desired file size, and then this event will fire to inform the virtual filesystem that it doesn't need to fill that space with zeros. Please refer to the Windows API's SetFileValidData function documentation for more information.

To handle this event properly, applications must perform any actions needed to update the specified file's valid data length.

The ValidDataLength parameter specifies the new valid data length, in bytes, for the file. This is the same value as passed to the Windows API's SetFileValidData function.

The HandleInfo parameter carries a handle to an object with information about the file handle. While within the event handler, it can be used to call any of the following methods: get_handle_creator_process_id, get_handle_creator_process_name, get_handle_creator_thread_id, or get_handle_creator_token. (This parameter may be absent, in which case it will be 0.)

The FileContext and HandleContext parameters are placeholders for application-defined data associated with the file and specific handle, respectively. Please refer to the Contexts topic for more information. (HandleContext may be absent, in which case it will be None.)

The ResultCode parameter will always be 0 when the event is fired. If the event cannot be handled in a "successful" manner for some reason (e.g., a resource isn't available, security checks failed, etc.), set it to a non-zero value to report an appropriate error. Please refer to the Error Reporting and Handling topic for more information.

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CBFS Connect 2020 Python Edition - Version 20.0 [Build 7880]