SetAllocationSize Event

Fires when the OS needs to set a file's allocation size.


class CBFSSetAllocationSizeEventParams {
  const QString &FileName();
  qint64 AllocationSize();
  qint64 HandleInfo();
  void *FileContext();
  void SetFileContext(void *lpFileContext);
  void *HandleContext();
  void SetHandleContext(void *lpHandleContext);
  int ResultCode();
  void SetResultCode(int iResultCode);
  int EventRetVal();
  void SetEventRetVal(int iRetVal);
// To handle, connect one or more slots to this signal. void SetAllocationSize(CBFSSetAllocationSizeEventParams *e);
// Or, subclass CBFS and override this emitter function. virtual int FireSetAllocationSize(CBFSSetAllocationSizeEventParams *e) {...}


This event fires when the OS (or the class, if the CorrectAllocationSizes configuration setting is enabled) needs to set the allocation size 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. SetFileSize
Allocation size The number of bytes allocated locally for the file. SetAllocationSize
Valid data length The number of bytes that have been written to the file. SetValidDataLength

To handle this event properly, applications must perform any actions needed to allocate the specified amount of space for the file in their backend storage. Please note that the file's actual size should not be changed; applications that do not track allocation size separately from file size should do nothing.

The AllocationSize parameter specifies the new allocation size of the file, in bytes. This value is typically larger than the file's actual size, as some file operations reserve space for the file before any data is actually written. Applications should track such situations and avoid re-allocating file space when possible to improve performance.

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: GetHandleCreatorProcessId, GetHandleCreatorProcessName, GetHandleCreatorThreadId, or GetHandleCreatorToken. (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 nullptr.)

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 Qt Edition - Version 20.0 [Build 8348]