ReadFile Event

Fires when the OS needs to read data from an open file.


virtual int FireReadFile(CBFSReadFileEventParams *e);
typedef struct {
const char *FileName;
int64 Position;
void *Buffer;
int64 BytesToRead;
int64 *pBytesRead;
int64 HandleInfo;
void *FileContext;
void *HandleContext;
int ResultCode; int reserved; } CBFSReadFileEventParams;
virtual INT FireReadFile(CBFSReadFileEventParams *e);
typedef struct {
LONG64 Position;
LPVOID Buffer;
LONG64 BytesToRead;
LONG64 *pBytesRead;
LONG64 HandleInfo;
LPVOID FileContext;
LPVOID HandleContext;
INT ResultCode; INT reserved; } CBFSReadFileEventParams;


This event fires when the OS needs to read data from the already-open file specified by FileName.

To handle this event properly, applications should read BytesToRead bytes of data from the specified file into the memory region pointed to by Buffer. Reading must begin at the specified Position in the file, and when reading is complete, applications must set BytesRead to reflect the actual number of bytes copied into Buffer. Applications must not attempt to copy more than BytesToRead bytes of data into Buffer.

Please refer to the Buffer Parameters topic for more information on how to work with memory buffer event parameters.

Note: While it is technically possible for an application to return fewer than BytesToRead bytes of data, doing so is abnormal, and should be avoided. Most processes treat read requests as "all or nothing", so returning less data than requested is likely to cause an ungraceful failure.

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]