on_set_valid_data_length Event
Fires when the OS needs to set a file's valid data length.
Syntax
class CBFSSetValidDataLengthEventParams(object): @property def file_name() -> str: ... @property def valid_data_length() -> int: ... @property def handle_info() -> int: ... @property def file_context() -> int: ... @file_context.setter def file_context(value) -> None: ... @property def handle_context() -> int: ... @handle_context.setter def handle_context(value) -> None: ... @property def result_code() -> int: ... @result_code.setter def result_code(value) -> None: ... # In class CBFS: @property def on_set_valid_data_length() -> Callable[[CBFSSetValidDataLengthEventParams], None]: ... @on_set_valid_data_length.setter def on_set_valid_data_length(event_hook: Callable[[CBFSSetValidDataLengthEventParams], None]) -> None: ...
Remarks
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.