FILE_STREAM_INFORMATION structure

The FILE_STREAM_INFORMATION structure is used to enumerate the streams for a file.

Syntax


typedef struct _FILE_STREAM_INFORMATION {
  ULONG         NextEntryOffset;
  ULONG         StreamNameLength;
  LARGE_INTEGER StreamSize;
  LARGE_INTEGER StreamAllocationSize;
  WCHAR         StreamName[1];
} FILE_STREAM_INFORMATION, *PFILE_STREAM_INFORMATION;

Members

NextEntryOffset

The offset of the next FILE_STREAM_INFORMATION entry. This member is zero if no other entries follow this one.

StreamNameLength

Length, in bytes, of the StreamName string.

StreamSize

Size, in bytes, of the stream.

StreamAllocationSize

File stream allocation size, in bytes. Usually this value is a multiple of the sector or cluster size of the underlying physical device.

StreamName

Unicode string that contains the name of the stream.

Remarks

The FILE_STREAM_INFORMATION structure is used to enumerate the streams for a file. This operation can be performed in either of the following ways:

  • By calling FltQueryInformationFile or ZwQueryInformationFile and specifying FileStreamInformation for the FileInformationClass parameter. On return, the FileInformation buffer contains a FILE_STREAM_INFORMATION structure for each file stream.

  • By sending an IRP_MJ_QUERY_INFORMATION request to the file system and specifying FileStreamInformation for the FileInformationClass parameter. On return, Irp->AssociatedIrp.SystemBuffer contains a FILE_STREAM_INFORMATION structure for each file stream.

No specific access rights are required to query this information. Thus this information is available as long as the file is open.

Support for stream enumeration is file system-dependent. If a file system does not support stream enumeration, it should return STATUS_INVALID_PARAMETER or STATUS_NOT_IMPLEMENTED for these requests.

If a file system supports stream enumeration, but the file has no streams other than the default data stream, which is unnamed, the file system should return a single FILE_STREAM_INFORMATION structure containing either "::$DATA" or a zero-length Unicode string as the StreamName.

NTFS returns "::$DATA" as the StreamName for the default data stream.

For a named data stream, NTFS appends ":$DATA" to the stream name. For example, for a user data stream with the name "Authors," NTFS returns ":Authors:$DATA" as the StreamName.

When calling a routine such as ZwCreateFile to open a named file stream, the ":$DATA" portion of the name can be omitted. For example, to open the "Authors" stream of a file named "Book," the caller can specify "Book:Authors" or "Book:Authors:$DATA" as the stream name. Both names are equivalent.

The size of the buffer passed in the FileInformation parameter to FltQueryInformationFile or ZwQueryInformationFile must be at least sizeof (FILE_STREAM_INFORMATION). If this buffer is not large enough to hold a FILE_STREAM_INFORMATION structure for each file stream, FltQueryInformationFile or ZwQueryInformationFile returns STATUS_BUFFER_OVERFLOW or STATUS_BUFFER_TOO_SMALL. Because such an unsuccessful call to FltQueryInformationFile or ZwQueryInformationFile does not return the required buffer size, filter drivers must make one or more additional calls to FltQueryInformationFile or ZwQueryInformationFile, passing a larger buffer in each call, until the buffer is large enough.

Support for named data streams is file-system-specific. File system filter drivers can determine whether a file system supports named streams in either of the following ways:

  • By calling FltQueryVolumeInformation or ZwQueryVolumeInformationFile and specifying FileFsAttributeInformation for the FsInformationClass parameter. On return, the FsInformation buffer contains a FILE_FS_ATTRIBUTE_INFORMATION structure. If the FILE_NAMED_STREAMS bit is set in the FileSystemAttributes member of this structure, the file system supports named streams.

  • By sending an IRP_MJ_QUERY_VOLUME_INFORMATION request to the file system and specifying FileFsAttributeInformation for the FsInformationClass parameter. On return, Irp->AssociatedIrp.SystemBuffer contains a FILE_FS_ATTRIBUTE_INFORMATION structure. If the FILE_NAMED_STREAMS bit is set in the FileSystemAttributes member of this structure, the file system supports named streams.

The FILE_STREAM_INFORMATION structure must be aligned on a LONGLONG (8-byte) boundary. If a buffer contains two or more of these structures, the NextEntryOffset value in each entry, except the last, falls on an 8-byte boundary.

Requirements

Header

Ntifs.h (include Ntifs.h or Fltkernel.h)

See also

FltQueryInformationFile
FltQueryVolumeInformation
IRP_MJ_QUERY_INFORMATION
IRP_MJ_QUERY_VOLUME_INFORMATION
ZwCreateFile
ZwQueryInformationFile
ZwQueryVolumeInformationFile

 

 

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