SetFileSize Event

Fires when the OS needs to change the size of an open file.


virtual int FireSetFileSize(CBFSSetFileSizeEventParams *e);
typedef struct {
const char *FileName;
int64 Size;
int64 HandleInfo;
void *FileContext;
void *HandleContext;
int ResultCode; int reserved; } CBFSSetFileSizeEventParams;
virtual INT FireSetFileSize(CBFSSetFileSizeEventParams *e);
typedef struct {
LONG64 Size;
LONG64 HandleInfo;
LPVOID FileContext;
LPVOID HandleContext;
INT ResultCode; INT reserved; } CBFSSetFileSizeEventParams;


This event fires when the OS needs to change the size of the already-open 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 resize the specified file in their backend storage.

The Size parameter specifies the new size of the file, in bytes. Extending a file does not require actual space to be allocated; however, NTFS allocates and zeroes the newly-added space, and some third-party applications might expect such behavior if the virtual filesystem is identified (via FileSystemName) as NTFS.

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 NULL.)

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 C++ Edition - Version 20.0 [Build 7545]