SetValidDataLength Event

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


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


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. 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

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 SetFileSize 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: 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]