cifs: documentation cleanup

Original Author

---------------

Steve French (sfrench@samba.org)

Steve French (smfrench@gmail.com, sfrench@samba.org)

The author wishes to express his appreciation and thanks to:

Andrew Tridgell (Samba team) for his early suggestions about smb/cifs VFS

Andrew Tridgell (Samba team) for his early suggestions about SMB/CIFS VFS

improvements. Thanks to IBM for allowing me time and test resources to pursue

this project, to Jim McDonough from IBM (and the Samba Team) for his help, to

the IBM Linux JFS team for explaining many esoteric Linux filesystem features.

- Ronnie Sahlberg (for SMB3 xattr work, bug fixes, and lots of great work on compounding)

- Shirish Pargaonkar (for many ACL patches over the years)

- Sachin Prabhu (many bug fixes, including for reconnect, copy offload and security)

- Paulo Alcantara

- Paulo Alcantara (for some excellent work in DFS, and in booting from SMB3)

- Long Li (some great work on RDMA, SMB Direct)

=======

See https://wiki.samba.org/index.php/LinuxCIFSKernel for summary

information (that may be easier to read than parsing the output of

"git log fs/cifs") about fixes/improvements to CIFS/SMB2/SMB3 support (changes

information about fixes/improvements to CIFS/SMB2/SMB3 support (changes

to cifs.ko module) by kernel version (and cifs internal module version).

This may be easier to read than parsing the output of "git log fs/cifs"

by release.

  protocol which was the successor to the Server Message Block

  (SMB) protocol, the native file sharing mechanism for most early

  PC operating systems. New and improved versions of CIFS are now

  called SMB2 and SMB3. Use of SMB3 (and later, including SMB3.1.1)

  is strongly preferred over using older dialects like CIFS due to

  security reasons. All modern dialects, including the most recent,

  SMB3.1.1 are supported by the CIFS VFS module. The SMB3 protocol

  is implemented and supported by all major file servers

  such as all modern versions of Windows (including Windows 2016

  Server), as well as by Samba (which provides excellent

  CIFS/SMB2/SMB3 server support and tools for Linux and many other

  operating systems).  Apple systems also support SMB3 well, as

  do most Network Attached Storage vendors, so this network

  filesystem client can mount to a wide variety of systems.

  It also supports mounting to the cloud (for example

  Microsoft Azure), including the necessary security features.

  called SMB2 and SMB3. Use of SMB3 (and later, including SMB3.1.1

  the most current dialect) is strongly preferred over using older

  dialects like CIFS due to security reasons. All modern dialects,

  including the most recent, SMB3.1.1, are supported by the CIFS VFS

  module. The SMB3 protocol is implemented and supported by all major

  file servers such as Windows (including Windows 2019 Server), as

  well as by Samba (which provides excellent CIFS/SMB2/SMB3 server

  support and tools for Linux and many other operating systems).

  Apple systems also support SMB3 well, as do most Network Attached

  Storage vendors, so this network filesystem client can mount to a

  wide variety of systems. It also supports mounting to the cloud

  (for example Microsoft Azure), including the necessary security

  features.

  The intent of this module is to provide the most advanced network

  file system function for SMB3 compliant servers, including advanced

  POSIX compliance, secure per-user session establishment, encryption,

  high performance safe distributed caching (leases/oplocks), optional packet

  signing, large files, Unicode support and other internationalization

  improvements. Since both Samba server and this filesystem client support

  the CIFS Unix extensions (and in the future SMB3 POSIX extensions),

  improvements. Since both Samba server and this filesystem client support the

  CIFS Unix extensions, and the Linux client also suppors SMB3 POSIX extensions,

  the combination can provide a reasonable alternative to other network and

  cluster file systems for fileserving in some Linux to Linux environments,

  not just in Linux to Windows (or Linux to Mac) environments.

a) SMB3 (and SMB3.1.1) missing optional features:

   - multichannel (started), integration with RDMA

   - directory leases (improved metadata caching), started (root dir only)

   - multichannel (partially integrated), integration of multichannel with RDMA

   - directory leases (improved metadata caching). Currently only implemented for root dir

   - T10 copy offload ie "ODX" (copy chunk, and "Duplicate Extents" ioctl

     currently the only two server side copy mechanisms supported)

b) improved sparse file support (fiemap and SEEK_HOLE are implemented

   but additional features would be supportable by the protocol).

   but additional features would be supportable by the protocol such

   as FALLOC_FL_COLLAPSE_RANGE and FALLOC_FL_INSERT_RANGE)

c) Directory entry caching relies on a 1 second timer, rather than

   using Directory Leases, currently only the root file handle is cached longer

   by leveraging Directory Leases

d) quota support (needs minor kernel change since quota calls

   to make it to network filesystems or deviceless filesystems)

d) quota support (needs minor kernel change since quota calls otherwise

    won't make it to network filesystems or deviceless filesystems).

e) Additional use cases can be optimized to use "compounding" (e.g.

   open/query/close and open/setinfo/close) to reduce the number of

   roundtrips to the server and improve performance. Various cases

   (stat, statfs, create, unlink, mkdir) already have been improved by

   (stat, statfs, create, unlink, mkdir, xattrs) already have been improved by

   using compounding but more can be done. In addition we could

   significantly reduce redundant opens by using deferred close (with

   handle caching leases) and better using reference counters on file

   metadata attributes easier from tools (e.g. extending what was done

   in smb-info tool).

l) encrypted file support

l) encrypted file support (currently the attribute showing the file is

   encrypted on the server is reported, but changing the attribute is not

   supported).

m) improved stats gathering tools (perhaps integration with nfsometer?)

   to extend and make easier to use what is currently in /proc/fs/cifs/Stats

o) mount helper GUI (to simplify the various configuration options on mount)

p) Add support for witness protocol (perhaps ioctl to cifs.ko from user space

   tool listening on witness protocol RPC) to allow for notification of share

   move, server failover, and server adapter changes.  And also improve other

   failover scenarios, e.g. when client knows multiple DFS entries point to

   different servers, and the server we are connected to has gone down.

p) Expand support for witness protocol to allow for notification of share

   move, and server network adapter changes. Currently only notifications by

   the witness protocol for server move is supported by the Linux client.

q) Allow mount.cifs to be more verbose in reporting errors with dialect

   or unsupported feature errors.

   or unsupported feature errors. This would now be easier due to the

   implementation of the new mount API.

r) updating cifs documentation, and user guide.

   secure) CIFS dialect can be disabled in environments that don't need it

   and simplify the code.

v) POSIX Extensions for SMB3.1.1 (started, create and mkdir support added

   so far).

v) Additional testing of POSIX Extensions for SMB3.1.1

w) Add support for additional strong encryption types, and additional spnego

   authentication mechanisms (see MS-SMB2)

   authentication mechanisms (see MS-SMB2).  GCM-256 is now partially implemented.

x) Finish support for SMB3.1.1 compression

There are additional mount options that may be helpful for SMB3 to get

improved POSIX behavior (NB: can use vers=3.0 to force only SMB3, never 2.1):

     ``mfsymlinks`` and ``cifsacl`` and ``idsfromsid``

   ``mfsymlinks`` and either ``cifsacl`` or ``modefromsid`` (usually with ``idsfromsid``)

Allowing User Mounts

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