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Subject[PATCH v5 01/13] ksmbd: add document
This adds a document describing ksmbd design, key features and usage.

Signed-off-by: Namjae Jeon <>
Signed-off-by: Sergey Senozhatsky <>
Signed-off-by: Hyunchul Lee <>
Acked-by: Ronnie Sahlberg <>
Signed-off-by: Steve French <>
Documentation/filesystems/cifs/index.rst | 10 ++
Documentation/filesystems/cifs/ksmbd.rst | 164 +++++++++++++++++++++++
Documentation/filesystems/index.rst | 2 +-
3 files changed, 175 insertions(+), 1 deletion(-)
create mode 100644 Documentation/filesystems/cifs/index.rst
create mode 100644 Documentation/filesystems/cifs/ksmbd.rst

diff --git a/Documentation/filesystems/cifs/index.rst b/Documentation/filesystems/cifs/index.rst
new file mode 100644
index 000000000000..1c8597a679ab
--- /dev/null
+++ b/Documentation/filesystems/cifs/index.rst
@@ -0,0 +1,10 @@
+.. toctree::
+ :maxdepth: 1
+ ksmbd
+ cifsroot
diff --git a/Documentation/filesystems/cifs/ksmbd.rst b/Documentation/filesystems/cifs/ksmbd.rst
new file mode 100644
index 000000000000..1e111efecd45
--- /dev/null
+++ b/Documentation/filesystems/cifs/ksmbd.rst
@@ -0,0 +1,164 @@
+.. 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 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 request, Forker
+thread will accept the client connection and fork a new thread for 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 take 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 connection is
+established with 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 clients 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 userspace process to, transfer user account and password that
+are registered using ksmbd.adduser(part of utils for user space). Further it
+allows sharing information parameters that 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) Planned for future.
+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 and GCM128 supported, GCM256 in
+ progress)
+SMB direct(RDMA) Partially Supported. SMB3 Multi-channel is
+ required to connect to Windows client.
+SMB3 Multi-channel In Progress.
+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 Planned for future.
+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.
+============================== =================================================
+How to run
+1. Download ksmbd-tools and compile them.
+ -
+2. Create user/password for SMB share.
+ # mkdir /etc/ksmbd/
+ # ksmbd.adduser -a <Enter USERNAME for SMB share access>
+3. Create /etc/ksmbd/smb.conf file, add SMB share in smb.conf file
+ - Refer smb.conf.example and
+4. Insert ksmbd.ko module
+ # insmod ksmbd.ko
+5. Start ksmbd user space daemon
+ # ksmbd.mountd
+6. Access share from Windows or Linux using CIFS
+Shutdown KSMBD
+1. kill user and kernel space daemon
+ # sudo ksmbd.control -s
+How to turn debug print on
+Each layer
+1. Enable all component prints
+ # sudo ksmbd.control -d "all"
+2. Enable one of components(smb, auth, vfs, oplock, ipc, conn, rdma)
+ # sudo ksmbd.control -d "smb"
+3. Show what prints are enable.
+ # 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.
diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst
index d4853cb919d2..bdba80ae2bb1 100644
--- a/Documentation/filesystems/index.rst
+++ b/Documentation/filesystems/index.rst
@@ -72,7 +72,7 @@ Documentation for filesystem implementations.
- cifs/cifsroot
+ cifs/index
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