FLT_PARAMETERS for IRP_MJ_READ union

The following union component is used when the MajorFunction field of the FLT_IO_PARAMETER_BLOCK structure for the operation is IRP_MJ_READ.

Syntax

typedef union _FLT_PARAMETERS {
  ...    ;
  struct {
    ULONG                   Length;
    ULONG POINTER_ALIGNMENT Key;
    LARGE_INTEGER           ByteOffset;
    PVOID                   ReadBuffer;
    PMDL                    MdlAddress;
  } Read;
  ...    ;
} FLT_PARAMETERS, *PFLT_PARAMETERS;

Members

• Read: Structure containing the following members.

• Length: Length, in bytes, of the data to be read.

• Key: Key value associated with a byte-range lock on the target file.

• ByteOffset: Starting byte offset within the file of the data to be read.

• ReadBuffer: Pointer to a buffer that receives the data that is read from the file. This member is optional and can be NULL if a MDL is provided in MdlAddress. See Remarks.

• MdlAddress: Address of a memory descriptor list (MDL) that describes the buffer that the ReadBuffer member points to. This member is optional and can be NULL if a buffer is provided in ReadBuffer. See Remarks.

Remarks

The FLT_PARAMETERS structure for IRP_MJ_READ operations contains the parameters for a read operation represented by a callback data (FLT_CALLBACK_DATA) structure. It is contained in an FLT_IO_PARAMETER_BLOCK structure.

If both a ReadBuffer and MdlAddress buffer are provided, it is recommended that minifilters use the MDL. The memory that ReadBuffer points to is valid when it is a user mode address being accessed within the context of the calling process, or if it is a kernel mode address.

If a minifilter changes the value of MdlAddress, then after its post operation callback, Filter Manager will free the MDL currently stored in MdlAddress and restore the previous value of MdlAddress.

IRP_MJ_READ can be an IRP-based operation or a fast I/O operation.

Requirements

See also

FLT_CALLBACK_DATA

FLT_IO_PARAMETER_BLOCK

FLT_IS_FASTIO_OPERATION

FLT_IS_FS_FILTER_OPERATION

FLT_IS_IRP_OPERATION

FLT_PARAMETERS

FltReadFile

IRP_MJ_READ

ZwReadFile