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linux-7.2.3/Documentation/filesystems/smb/cifsroot.rst
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.. SPDX-License-Identifier: GPL-2.0
===========================================
Mounting root file system via SMB (cifs.ko)
===========================================
Written 2019 by Paulo Alcantara <palcantara@suse.de>
Written 2019 by Aurelien Aptel <aaptel@suse.com>
The CONFIG_CIFS_ROOT option enables experimental root file system
support over the SMB protocol via cifs.ko.
It introduces a new kernel command-line option called 'cifsroot='
which will tell the kernel to mount the root file system over the
network by utilizing SMB or CIFS protocol.
In order to mount, the network stack will also need to be set up by
using 'ip=' config option. For more details, see
Documentation/admin-guide/nfs/nfsroot.rst.
A CIFS root mount currently requires the use of SMB1+UNIX Extensions
which is only supported by the Samba server. SMB1 is the older
deprecated version of the protocol but it has been extended to support
POSIX features (See [1]). The equivalent extensions for the newer
recommended version of the protocol (SMB3) have not been fully
implemented yet which means SMB3 doesn't support some required POSIX
file system objects (e.g. block devices, pipes, sockets).
As a result, a CIFS root will default to SMB1 for now but the version
to use can nonetheless be changed via the 'vers=' mount option. This
default will change once the SMB3 POSIX extensions are fully
implemented.
Server configuration
====================
To enable SMB1+UNIX extensions you will need to set these global
settings in Samba smb.conf::
[global]
server min protocol = NT1
unix extension = yes # default
Kernel command line
===================
::
root=/dev/cifs
This is just a virtual device that basically tells the kernel to mount
the root file system via SMB protocol.
::
cifsroot=//<server-ip>/<share>[,options]
Enables the kernel to mount the root file system via SMB that are
located in the <server-ip> and <share> specified in this option.
The default mount options are set in fs/smb/client/cifsroot.c.
server-ip
IPv4 address of the server.
share
Path to SMB share (rootfs).
options
Optional mount options. For more information, see mount.cifs(8).
Examples
========
Export root file system as a Samba share in smb.conf file::
...
[linux]
path = /path/to/rootfs
read only = no
guest ok = yes
force user = root
force group = root
browseable = yes
writeable = yes
admin users = root
public = yes
create mask = 0777
directory mask = 0777
...
Restart smb service::
# systemctl restart smb
Test it under QEMU on a kernel built with CONFIG_CIFS_ROOT and
CONFIG_IP_PNP options enabled::
# qemu-system-x86_64 -enable-kvm -cpu host -m 1024 \
-kernel /path/to/linux/arch/x86/boot/bzImage -nographic \
-append "root=/dev/cifs rw ip=dhcp cifsroot=//10.0.2.2/linux,username=foo,password=bar console=ttyS0 3"
1: https://wiki.samba.org/index.php/UNIX_Extensions
linux-7.2.3/Documentation/filesystems/smb/index.rst
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===============================
CIFS
===============================
.. toctree::
:maxdepth: 1
ksmbd
cifsroot
smbdirect
linux-7.2.3/Documentation/filesystems/smb/ksmbd.rst
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.. SPDX-License-Identifier: GPL-2.0
==========================
KSMBD - SMB3 Kernel Server
==========================
KSMBD is a linux kernel server which implements SMB3 protocol in kernel space
for sharing files over network.
KSMBD architecture
==================
The subset of performance related operations belong in kernelspace and
the other subset which belong to operations which are not really related with
performance in userspace. So, DCE/RPC management that has historically resulted
into a number of buffer overflow issues and dangerous security bugs and user
account management are implemented in user space as ksmbd.mountd.
File operations that are related with performance (open/read/write/close etc.)
in kernel space (ksmbd). This also allows for easier integration with VFS
interface for all file operations.
ksmbd (kernel daemon)
---------------------
When the server daemon is started, It starts up a forker thread
(ksmbd/interface name) at initialization time and open a dedicated port 445
for listening to SMB requests. Whenever new clients make a request, the Forker
thread will accept the client connection and fork a new thread for a dedicated
communication channel between the client and the server. It allows for parallel
processing of SMB requests(commands) from clients as well as allowing for new
clients to make new connections. Each instance is named ksmbd/1~n(port number)
to indicate connected clients. Depending on the SMB request types, each new
thread can decide to pass through the commands to the user space (ksmbd.mountd),
currently DCE/RPC commands are identified to be handled through the user space.
To further utilize the linux kernel, it has been chosen to process the commands
as workitems and to be executed in the handlers of the ksmbd-io kworker threads.
It allows for multiplexing of the handlers as the kernel takes care of initiating
extra worker threads if the load is increased and vice versa, if the load is
decreased it destroys the extra worker threads. So, after the connection is
established with the client. Dedicated ksmbd/1..n(port number) takes complete
ownership of receiving/parsing of SMB commands. Each received command is worked
in parallel i.e., there can be multiple client commands which are worked in
parallel. After receiving each command a separated kernel workitem is prepared
for each command which is further queued to be handled by ksmbd-io kworkers.
So, each SMB workitem is queued to the kworkers. This allows the benefit of load
sharing to be managed optimally by the default kernel and optimizing client
performance by handling client commands in parallel.
ksmbd.mountd (user space daemon)
--------------------------------
ksmbd.mountd is a userspace process to, transfer the user account and password that
are registered using ksmbd.adduser (part of utils for user space). Further it
allows sharing information parameters that are parsed from smb.conf to ksmbd in
kernel. For the execution part it has a daemon which is continuously running
and connected to the kernel interface using netlink socket, it waits for the
requests (dcerpc and share/user info). It handles RPC calls (at a minimum few
dozen) that are most important for file server from NetShareEnum and
NetServerGetInfo. Complete DCE/RPC response is prepared from the user space
and passed over to the associated kernel thread for the client.
KSMBD Feature Status
====================
============================== =================================================
Feature name Status
============================== =================================================
Dialects Supported. SMB2.1 SMB3.0, SMB3.1.1 dialects
(intentionally excludes security vulnerable SMB1
dialect).
Auto Negotiation Supported.
Compound Request Supported.
Oplock Cache Mechanism Supported.
SMB2 leases(v1 lease) Supported.
Directory leases(v2 lease) Supported.
Multi-credits Supported.
NTLM/NTLMv2 Supported.
HMAC-SHA256 Signing Supported.
Secure negotiate Supported.
Signing Update Supported.
Pre-authentication integrity Supported.
SMB3 encryption(CCM, GCM) Supported. (CCM/GCM128 and CCM/GCM256 supported)
SMB direct(RDMA) Supported.
SMB3 Multi-channel Partially Supported. Planned to implement
replay/retry mechanisms for future.
Receive Side Scaling mode Supported.
SMB3.1.1 POSIX extension Supported.
ACLs Partially Supported. only DACLs available, SACLs
(auditing) is planned for the future. For
ownership (SIDs) ksmbd generates random subauth
values(then store it to disk) and use uid/gid
get from inode as RID for local domain SID.
The current acl implementation is limited to
standalone server, not a domain member.
Integration with Samba tools is being worked on
to allow future support for running as a domain
member.
Kerberos Supported.
Durable handle v1,v2 Supported.
Persistent handle Planned for future.
SMB2 notify Planned for future.
Sparse file support Supported.
DCE/RPC support Partially Supported. a few calls(NetShareEnumAll,
NetServerGetInfo, SAMR, LSARPC) that are needed
for file server handled via netlink interface
from ksmbd.mountd. Additional integration with
Samba tools and libraries via upcall is being
investigated to allow support for additional
DCE/RPC management calls (and future support
for Witness protocol e.g.)
ksmbd/nfsd interoperability Planned for future. The features that ksmbd
support are Leases, Notify, ACLs and Share modes.
SMB3.1.1 Compression Supported.
SMB3.1.1 over QUIC Planned for future.
Signing/Encryption over RDMA Planned for future.
SMB3.1.1 GMAC signing support Planned for future.
============================== =================================================
How to run
==========
1. Download ksmbd-tools(https://github.com/cifsd-team/ksmbd-tools/releases) and
compile them.
- Refer to README(https://github.com/cifsd-team/ksmbd-tools/blob/master/README.md)
to know how to use ksmbd.mountd/adduser/addshare/control utils
$ ./autogen.sh
$ ./configure --with-rundir=/run
$ make && sudo make install
2. Create /usr/local/etc/ksmbd/ksmbd.conf file, add SMB share in ksmbd.conf file.
- Refer to ksmbd.conf.example in ksmbd-utils, See ksmbd.conf manpage
for details to configure shares.
$ man ksmbd.conf
3. Create user/password for SMB share.
- See ksmbd.adduser manpage.
$ man ksmbd.adduser
$ sudo ksmbd.adduser -a <Enter USERNAME for SMB share access>
4. Insert the ksmbd.ko module after you build your kernel. No need to load the module
if ksmbd is built into the kernel.
- Set ksmbd in menuconfig(e.g. $ make menuconfig)
[*] Network File Systems --->
<M> SMB3 server support (EXPERIMENTAL)
$ sudo modprobe ksmbd.ko
5. Start ksmbd user space daemon
$ sudo ksmbd.mountd
6. Access share from Windows or Linux using SMB3 client (cifs.ko or smbclient of samba)
Shutdown KSMBD
==============
1. kill user and kernel space daemon
# sudo ksmbd.control -s
How to turn debug print on
==========================
Each layer
/sys/class/ksmbd-control/debug
1. Enable all component prints
# sudo ksmbd.control -d "all"
2. Enable one of the components (smb, auth, vfs, oplock, ipc, conn, rdma)
# sudo ksmbd.control -d "smb"
3. Show what prints are enabled.
# cat /sys/class/ksmbd-control/debug
[smb] auth vfs oplock ipc conn [rdma]
4. Disable prints:
If you try the selected component once more, It is disabled without brackets.
linux-7.2.3/Documentation/filesystems/smb/smbdirect.rst
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.. SPDX-License-Identifier: GPL-2.0
===========================
SMB Direct - SMB3 over RDMA
===========================
This document describes how to set up the Linux SMB client and server to
use RDMA.
Overview
========
The Linux SMB kernel client supports SMB Direct, which is a transport
scheme for SMB3 that uses RDMA (Remote Direct Memory Access) to provide
high throughput and low latencies by bypassing the traditional TCP/IP
stack.
SMB Direct on the Linux SMB client can be tested against KSMBD - a
kernel-space SMB server.
Installation
=============
- Install an RDMA device. As long as the RDMA device driver is supported
by the kernel, it should work. This includes both software emulators (soft
RoCE, soft iWARP) and hardware devices (InfiniBand, RoCE, iWARP).
- Install a kernel with SMB Direct support. The first kernel release to
support SMB Direct on both the client and server side is 5.15. Therefore,
a distribution compatible with kernel 5.15 or later is required.
- Install cifs-utils, which provides the `mount.cifs` command to mount SMB
shares.
- Configure the RDMA stack
Make sure that your kernel configuration has RDMA support enabled. Under
Device Drivers -> Infiniband support, update the kernel configuration to
enable Infiniband support.
Enable the appropriate IB HCA support or iWARP adapter support,
depending on your hardware.
If you are using InfiniBand, enable IP-over-InfiniBand support.
For soft RDMA, enable either the soft iWARP (`RDMA _SIW`) or soft RoCE
(`RDMA_RXE`) module. Install the `iproute2` package and use the
`rdma link add` command to load the module and create an
RDMA interface.
e.g. if your local ethernet interface is `eth0`, you can use:
.. code-block:: bash
sudo rdma link add siw0 type siw netdev eth0
- Enable SMB Direct support for both the server and the client in the kernel
configuration.
Server Setup
.. code-block:: text
Network File Systems --->
<M> SMB3 server support
[*] Support for SMB Direct protocol
Client Setup
.. code-block:: text
Network File Systems --->
<M> SMB3 and CIFS support (advanced network filesystem)
[*] SMB Direct support
- Build and install the kernel. SMB Direct support will be enabled in the
cifs.ko and ksmbd.ko modules.
Setup and Usage
================
- Set up and start a KSMBD server as described in the `KSMBD documentation
<https://www.kernel.org/doc/Documentation/filesystems/smb/ksmbd.rst>`_.
Also add the "server multi channel support = yes" parameter to ksmbd.conf.
- On the client, mount the share with `rdma` mount option to use SMB Direct
(specify a SMB version 3.0 or higher using `vers`).
For example:
.. code-block:: bash
mount -t cifs //server/share /mnt/point -o vers=3.1.1,rdma
- To verify that the mount is using SMB Direct, you can check dmesg for the
following log line after mounting:
.. code-block:: text
CIFS: VFS: RDMA transport established
Or, verify `rdma` mount option for the share in `/proc/mounts`:
.. code-block:: bash
cat /proc/mounts | grep cifs