PFREE_FUNCTION function pointer
A file system legacy filter driver can register a PFREE_FUNCTION typed routine as the filter's FreeCallback callback routine. The file system calls FreeCallback when the file system removes a file context object by using FsRtlTeardownPerFileContexts or removes a stream context object by using FsRtlTeardownPerStreamContexts.
You must declare the callback routine by using the FREE_FUNCTION type. For more information, see the example in the Remarks section.
Syntax
typedef VOID ( *FreeCallback)(
_In_ PVOID Buffer
);
Parameters
- Buffer [in]: A pointer to the FSRTL_PER_FILE_CONTEXT or the FSRTL_PER_STREAM_CONTEXT structure to be freed.
Return value
None
Remarks
When a file system tears down the per-file context object for a file, it must call FsRtlTeardownPerFileContexts. This routine calls the FreeCallback routines of all per-file context structures associated with the file. This callback routine must free any memory used for the FSRTL_PER_FILE_CONTEXT object and any associated context information. This is also the case for per-stream contexts when FsRtlTeardownPerStreamContexts is called and FreeCallback will free memory used for FSRTL_PER_STREAM_CONTEXT objects.
For remarks about synchronizing access to per-file context objects or to per-stream context objects during a call to FreeCallback, see FsRtlTeardownPerFileContexts and FsRtlTeardownPerStreamContexts.
Note
The FreeCallback routine cannot recursively call down into the file system or acquire any file system resources.
To define a FreeCallback callback function that is named MyFreeFunction, you must first provide a function declaration that the Static Driver Verifier (SDV) and other verification tools require, as follows:
FREE_FUNCTION MyFreeFunction;
And then implement your callback function as follows:
VOID
MyFreeFunction (
__in PVOID Buffer
)
{...}
Requirements
| Requirement type | Requirement |
|---|---|
| Minimum supported client | Windows Vista |
| Header | Wdm.h (include Wdm.h or Ntddk.h) |
| IRQL | <= APC_LEVEL |
See also
FsRtlTeardownPerStreamContexts
Tracking Per-File Context in a Legacy File System Filter Driver
Tracking Per-Stream Context in a Legacy File System Filter Driver