FltReadFile

FltReadFile 从一个打开的文件、流或者设备中读取数据。

NTSTATUS
  FltReadFile(
    IN PFLT_INSTANCE  InitiatingInstance,
    IN PFILE_OBJECT  FileObject,
    IN PLARGE_INTEGER  ByteOffset OPTIONAL,
    IN ULONG  Length,
    OUT PVOID  Buffer,
    IN FLT_IO_OPERATION_FLAGS  Flags,
    OUT PULONG  BytesRead OPTIONAL,
    IN PFLT_COMPLETED_ASYNC_IO_CALLBACK  CallbackRoutine OPTIONAL,
    IN PVOID  CallbackContext OPTIONAL
    ); 

参数

InitiatingInstance

Opaque instance pointer for the minifilter driver instance that is initiating the read request. This parameter is required and cannot be NULL.

FileObject

Pointer to a file object for the file that the data is to be read from. This file object must be currently open. Calling FltReadFile when the file object is not yet open or is no longer open (for example, in a pre-create or post-cleanup callback routine) causes the system to ASSERT on a checked build. This parameter is required and cannot be NULL.

ByteOffset

Pointer to a caller-allocated variable that specifies the starting byte offset within the file where the read operation is to begin.If this offset is supplied, or if the FLTFL_IO_OPERATION_DO_NOT_UPDATE_BYTE_OFFSET flag is specified in the Flags parameter, FltReadFile does not update the file object’s CurrentByteOffset field.If the file object that FileObject points to was opened for synchronous I/O, the caller of FltReadFile can specify that the current file position offset be used instead of an explicit ByteOffset value by setting this parameter to NULL. If the current file position is used, FltReadFile updates the file object’s CurrentByteOffset field by adding the number of bytes read when it completes the read operation.

If the file object that FileObject points to was opened for asynchronous I/O, this parameter is required and cannot be NULL.

Length

Size, in bytes, of the buffer that the Buffer parameter points to.

Buffer

Pointer to a caller-allocated buffer that receives the data that is read from the file.

Flags

Bitmask of flags specifying the type of read operation to be performed.

标志	含义
FLTFL_IO_OPERATION_DO_NOT_UPDATE_BYTE_OFFSET	Minifilter drivers can set this flag to specify that FltReadFile should not update the file object’s CurrentByteOffset field.
FLTFL_IO_OPERATION_NON_CACHED	Minifilter drivers can set this flag to specify a noncached read, even if the file object was not opened with FILE_NO_INTERMEDIATE_BUFFERING.
FLTFL_IO_OPERATION_PAGING	Minifilter drivers can set this flag to specify a paging read.

 

BytesRead

Pointer to a caller-allocated variable that receives the number of bytes read from the file. If CallbackRoutine is not NULL, this parameter is ignored. Otherwise, this parameter is optional and can be NULL.

CallbackRoutine

Pointer to a PFLT_COMPLETED_ASYNC_IO_CALLBACK-typed callback routine to call when the read operation is complete. This parameter is optional and can be NULL.

CallbackContext

Context pointer to be passed to the CallbackRoutine if one is present. This parameter is optional and can be NULL. If CallbackRoutine is NULL, this parameter is ignored. 

返回值

FltReadFile returns the NTSTATUS value that was returned by the file system.

注释

微过滤器调用 FltReadFile 从一个打开的文件中读取数据。

FltReadFile 创建一个读请求并发送到微过滤器驱动挂载的进程后到文件系统。指定的进程之上的挂载进程则收不到读请求。

FltReadFile 在下列条件成立时，准备非缓存I/O：

• 调用者在参数 Flags 中设置了 FLTFL_IO_OPERATION_NON_CACHED 标志；
• 文件对象使用非缓存I/O打开的。通常是在调用 FltCreateFile, FltCreateFileEx, 或 ZwCreateFile 时，在参数CreateOptions 标志中指定了FILE_NO_INTERMEDIATE_BUFFERING 。 

Noncached I/O imposes the following restrictions on the parameter values passed to FltReadFile:

• The buffer that the Buffer parameter points to must be aligned in accordance with the alignment requirement of the underlying storage device. To allocate such an aligned buffer, call FltAllocatePoolAlignedWithTag.
• The byte offset that the ByteOffset parameter points to must be a nonnegative multiple of the volume’s sector size.
• The length specified in the Length parameter must be a nonnegative multiple of the volume’s sector size.

If an attempt is made to read beyond the end of the file, FltReadFile returns an error.

If the value of the CallbackRoutine parameter is not NULL, the read operation is performed asynchronously.

If the value of the CallbackRoutine parameter is NULL, the read operation is performed synchronously. That is, FltReadFile waits until the read operation is complete before returning. This is true even if the file object that FileObject points to was opened for asynchronous I/O.

If multiple threads call FltReadFile for the same file object, and the file object was opened for synchronous I/O, the Filter Manager does not attempt to serialize I/O on the file. In this respect, FltReadFile differs from ZwReadFile.

Requirements

IRQL: PASSIVE_LEVEL

Headers: Declared in fltkernel.h. Include fltkernel.h.