CcInitializeCacheMap function

File systems call the CcInitializeCacheMap routine to cache a file.

Syntax

NTKERNELAPI VOID CcInitializeCacheMap(
  PFILE_OBJECT             FileObject,
  PCC_FILE_SIZES           FileSizes,
  BOOLEAN                  PinAccess,
  PCACHE_MANAGER_CALLBACKS Callbacks,
  PVOID                    LazyWriteContext
);

Parameters

FileObject

Pointer to a file object for the file.

FileSizes

Pointer to a CC_FILE_SIZES structure containing AllocationSize, FileSize, and ValidDataLength for the file. This structure is defined as follows:

typedef struct _CC_FILE_SIZES {
    LARGE_INTEGER AllocationSize;
    LARGE_INTEGER FileSize;
    LARGE_INTEGER ValidDataLength;
} CC_FILE_SIZES, *PCC_FILE_SIZES;
Member Meaning
AllocationSize New section object size for the file. Ignored if less than or equal to the current section size.
FileSize New file size for the file.
ValidDataLength New valid data length for the file.
PinAccess Set to TRUE if CcPinXxx routines will be used on the file. Callbacks Pointer to a structure allocated from nonpaged pool, containing entry points of caller-supplied read-ahead and write-behind callback routines.This structure and its members are defined as follows:
typedef struct _CACHE_MANAGER_CALLBACKS {
    PACQUIRE_FOR_LAZY_WRITE AcquireForLazyWrite;
    PRELEASE_FROM_LAZY_WRITE ReleaseFromLazyWrite;
    PACQUIRE_FOR_READ_AHEAD AcquireForReadAhead;
    PRELEASE_FROM_READ_AHEAD ReleaseFromReadAhead;
} CACHE_MANAGER_CALLBACKS, *PCACHE_MANAGER_CALLBACKS;
typedef
BOOLEAN (*PACQUIRE_FOR_LAZY_WRITE) (
             IN PVOID Context,
             IN BOOLEAN Wait
             );
typedef
VOID (*PRELEASE_FROM_LAZY_WRITE) (
             IN PVOID Context
             );
typedef
BOOLEAN (*PACQUIRE_FOR_READ_AHEAD) (
             IN PVOID Context,
             IN BOOLEAN Wait
             );
typedef
VOID (*PRELEASE_FROM_READ_AHEAD) (
             IN PVOID Context
             );

LazyWriteContext

Pointer to context information to be passed to the callback routines specified in Callbacks.

Return Value

None

Remarks

CcInitializeCacheMap creates the data structures required for file data caching.

If any failure occurs, CcInitializeCacheMap raises a status exception for that particular failure. For example, if a pool allocation failure occurs, CcInitializeCacheMap raises a STATUS_INSUFFICIENT_RESOURCES exception. Therefore, to gain control if a failure occurs, the driver should wrap the call to CcInitializeCacheMap in a try-except or try-finally statement.

File systems must call CcInitializeCacheMap to cache a file before using any other cache manager routines on the file, unless the file was created with data caching disabled. In most file systems, file caching is enabled by default, but can be disabled by setting the FILE_NO_INTERMEDIATE_BUFFERING flag to TRUE in the file create options.

After calling CcInitializeCacheMap, the file system can call CcSetAdditionalCacheAttributes to disable read-ahead or write-behind, if desired.

When closing a file, every file system that supports file caching must call CcUninitializeCacheMap on that file, whether the file is cached or not. Even if the file was created with caching disabled, the file system still must call CcUninitializeCacheMap.

The CcIsFileCached macro determines whether a file is cached or not.

C++
BOOLEAN CcIsFileCached(
  [in] PFILE_OBJECT FileObject
);
Parameters FileObject[in] [in] Pointer to a file object for the file. Return value Returns TRUE if the file is cached, FALSE otherwise.
Note Because multiple file objects can refer to the same file (that is, data stream), it is possible for the CcIsFileCached macro to return TRUE given a non-cached file object if another cached file object refers to the same data stream. In other words, if there is a set of file objects that refer to the same data stream and if at least one of the file objects in the set is cached, CcIsFileCached will return TRUE for all file objects in the set.

Requirements

   
Target Platform Universal
Header ntifs.h (include Ntifs.h)
Library NtosKrnl.lib
DLL NtosKrnl.exe

See Also

CcSetAdditionalCacheAttributes

CcUninitializeCacheMap