[POSIX-FSCC] POSIX Extensions to MS-FSCC

Specifies the MS-FSCC extensions for supporting POSIX compliant operating systems.

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1 Introduction

The SMB3 POSIX Extensions are extensions to enable POSIX compliant operating systems to better interoperate with SMB3 servers and storage appliances. This document specified the extensions to the [MS-FSCC] specification. Popular servers such as Samba, Windows Server and others support SMB3 by default. These extensions are already implemented in multiple clients and servers.

2 Messages and Structures

2.3 Structures

2.3.1 File Information Classes

Refer to section 2.4 of [MS-FSCC] for additional details. This section only explains details relevant to the FilePosixInformation info class.

2.3.1.1 FilePosixInformation

This information class is used to query file posix information.

A FILE_POSIX_INFORMATION data element, defined as follows, is returned by the server.

CreationTime (8 bytes): The time when the file was created; see section 2.1.1 of [MS-FSCC]. A valid time for this field is an integer greater than or equal to 0. When setting file attributes, a value of 0 indicates to the server that it MUST NOT change this attribute. When setting file attributes, a value of -1 indicates to the server that it MUST NOT change this attribute for all subsequent operations on the same file handle. When setting file attributes, a value of -2 indicates to the server that it MUST change this attribute for all subsequent operations on the same file handle. This field MUST NOT be set to a value less than -2.

LastAccessTime (8 bytes): The last time the file was accessed; see section 2.1.1 of [MS-FSCC]. A valid time for this field is an integer greater than or equal to 0. When setting file attributes, a value of 0 indicates to the server that it MUST NOT change this attribute. When setting file attributes, a value of -1 indicates to the server that it MUST NOT change this attribute for all subsequent operations on the same file handle. When setting file attributes, a value of -2 indicates to the server that it MUST change this attribute for all subsequent operations on the same file handle. This field MUST NOT be set to a value less than -2.

LastWriteTime (8 bytes): The last time information was written to the file; see section 2.1.1 of [MS-FSCC]. A valid time for this field is an integer greater than or equal to 0. When setting file attributes, a value of 0 indicates to the server that it MUST NOT change this attribute. When setting file attributes, a value of -1 indicates to the server that it MUST NOT change this attribute for all subsequent operations on the same file handle. When setting file attributes, a value of -2 indicates to the server that it MUST change this attribute for all subsequent operations on the same file handle. This field MUST NOT be set to a value less than -2.

ChangeTime (8 bytes): The last time the file was changed; see section 2.1.1 of [MS-FSCC]. A valid time for this field is an integer greater than or equal to 0. When setting file attributes, a value of 0 indicates to the server that it MUST NOT change this attribute. When setting file attributes, a value of -1 indicates to the server that it MUST NOT change this attribute for all subsequent operations on the same file handle. When setting file attributes, a value of -2 indicates to the server that it MUST change this attribute for all subsequent operations on the same file handle. This field MUST NOT be set to a value less than -2.

EndOfFile (8 bytes): The size of the file.

AllocationSize (8 bytes): The size allocated on disk for the file.

FileAttributes (4 bytes): A 32-bit unsigned integer that contains the file attributes. Valid file attributes are specified in section 2.6 of [MS-FSCC].

Inode (8 bytes): The POSIX inode for the file.

FileId (4 bytes): The POSIX fileId for the file.

Reserved (4 bytes): A 32-bit field. This field is reserved. This field can be set to any value, and MUST be ignored.

NumberOfLinks (4 bytes): The number of hard links to the file.

ReparseTag (4 bytes): The reparse tag, as defined in section 2.1.2.1 of [MS-FSCC].

POSIXPerms (4 bytes): The posix permissions for the opened file as defined in section 4.5 of IEEE Std 1003.1-2017.

OwnerSID (variable): The owner SID as defined in Microsoft Security identifiers.

GroupSID (variable): The group SID as defined in Microsoft Security identifiers.

FilenameLength (4 bytes): The length, in bytes, of the filename.

Filename (variable): A variable-length buffer containing the filename, the length specified by FilenameLength.

2.3.2 File System Information Classes

Refer to section 2.5 of [MS-FSCC] for additional details. This section only explains details relevant to the FileFsPosixInformation info class.

2.3.2.1 FileFsPosixInformation

This information class is used to query file system posix information.

A FILE_FS_POSIX_INFORMATION data element, defined as follows, is returned by the server.

OptimalTransferSize (4 bytes): The preferred length of I/O requests for files on this file system., from struct statvfs.f_bsize.

BlockSize (4 bytes): The size in bytes of the minimum unit of allocation on this filesystem, from struct statvfs.f_frsize.

TotalBlocks (8 bytes): Size of filesystem in BlockSize units, from struct statvfs.f_blocks.

BlocksAvailable (8 bytes): Number of free blocks in BlockSize units, from struct statvfs.f_bfree.

UserBlocksAvailable (8 bytes): Number of free blocks for unprivileged users in BlockSize units, from struct statvfs.f_bavail.

TotalFileNodes (8 bytes): Number of inodes, from struct statvfs.f_files.

FreeFileNodes (8 bygtes): Number of free inodes, from struct statvfs.f_ffree.

FsIdentifier (8 bytes): Filesystem ID, from struct statvfs.f_fsid.