Edit

FLT_PARAMETERS for IRP_MJ_MDL_READ union

  • Article

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

Syntax

typedef union _FLT_PARAMETERS {
  ...    ;
  struct {
    LARGE_INTEGER           FileOffset;
    ULONG POINTER_ALIGNMENT Length;
    ULONG POINTER_ALIGNMENT Key;
    PMDL                    *MdlChain;
  } MdlRead;
  ...    ;
} FLT_PARAMETERS, *PFLT_PARAMETERS;

Members

  • MdlRead: Structure containing the following members.

  • FileOffset: Starting byte within the cached file.

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

  • Key: Key value associated with a byte-range lock on the target file. If the range to be read overlaps or is a subrange of an exclusively locked range within the file, this parameter must be the key for that exclusive lock. The exclusive lock must be held by the parent process of the calling thread; otherwise, this parameter is ignored.

  • MdlChain: Pointer to a variable that receives a pointer to a chain of one or more memory descriptor lists (MDL) that describe the pages containing the data to be read.

Remarks

The FLT_PARAMETERS structure for IRP_MJ_MDL_READ operations contains the parameters for a fast I/O MdlRead operation represented by a callback data (FLT_CALLBACK_DATA) structure. It is contained in an FLT_IO_PARAMETER_BLOCK structure.

If a fast I/O IRP_MJ_MDL_READ request fails, the issuer of the I/O determines how to reissue the request. A minifilter may not always get an IRP-based IRP_MJ_MDL_READ. For instance, the IRP request could be reissued as IRP_MJ_READ/IRP_MN_MDL.

IRP_MJ_MDL_READ is a fast I/O operation.

Requirements

Requirement type Requirement
Header Fltkernel.h (include Fltkernel.h)

See also

FLT_CALLBACK_DATA

FLT_IO_PARAMETER_BLOCK

FLT_IS_FASTIO_OPERATION

FLT_IS_FS_FILTER_OPERATION

FLT_IS_IRP_OPERATION

FLT_PARAMETERS