linux-kernel - Re: [PATCH v2 00/10] cifsd: introduce new SMB3 kernel server

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Message-ID: <20210427205331.GA15168@fieldses.org>
Date:   Tue, 27 Apr 2021 16:53:31 -0400
From:   bfields@...ldses.org (J. Bruce Fields)
To:     Namjae Jeon <namjae.jeon@...sung.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        smfrench@...il.com, senozhatsky@...omium.org, hyc.lee@...il.com,
        viro@...iv.linux.org.uk, hch@....de, hch@...radead.org,
        ronniesahlberg@...il.com, aurelien.aptel@...il.com,
        aaptel@...e.com, sandeen@...deen.net, dan.carpenter@...cle.com,
        colin.king@...onical.com, rdunlap@...radead.org,
        willy@...radead.org
Subject: Re: [PATCH v2 00/10] cifsd: introduce new SMB3 kernel server

On Thu, Apr 22, 2021 at 09:28:14AM +0900, Namjae Jeon wrote:
> This is the patch series for cifsd(ksmbd) kernel server.
> 
> What is cifsd(ksmbd) ?
> ======================
> 
> The SMB family of protocols is the most widely deployed
> network filesystem protocol, the default on Windows and Macs (and even
> on many phones and tablets), with clients and servers on all major
> operating systems, but lacked a kernel server for Linux. For many
> cases the current userspace server choices were suboptimal
> either due to memory footprint, performance or difficulty integrating
> well with advanced Linux features.
> 
> ksmbd is a new kernel module which implements the server-side of the SMB3 protocol.
> The target is to provide optimized performance, GPLv2 SMB server, better
> lease handling (distributed caching). The bigger goal is to add new
> features more rapidly (e.g. RDMA aka "smbdirect", and recent encryption
> and signing improvements to the protocol) which are easier to develop
> on a smaller, more tightly optimized kernel server than for example
> in Samba.  The Samba project is much broader in scope (tools, security services,
> LDAP, Active Directory Domain Controller, and a cross platform file server
> for a wider variety of purposes) but the user space file server portion
> of Samba has proved hard to optimize for some Linux workloads, including
> for smaller devices. This is not meant to replace Samba, but rather be
> an extension to allow better optimizing for Linux, and will continue to
> integrate well with Samba user space tools and libraries where appropriate.
> Working with the Samba team we have already made sure that the configuration
> files and xattrs are in a compatible format between the kernel and
> user space server.
> 
> 
> Architecture
> ============
> 
>                |--- ...
>        --------|--- ksmbd/3 - Client 3
>        |-------|--- ksmbd/2 - Client 2
>        |       |         ____________________________________________________
>        |       |        |- Client 1                                          |
> <--- Socket ---|--- ksmbd/1   <<= Authentication : NTLM/NTLM2, Kerberos      |
>        |       |      | |     <<= SMB engine : SMB2, SMB2.1, SMB3, SMB3.0.2, |
>        |       |      | |                SMB3.1.1                            |
>        |       |      | |____________________________________________________|
>        |       |      |
>        |       |      |--- VFS --- Local Filesystem
>        |       |
> KERNEL |--- ksmbd/0(forker kthread)
> ---------------||---------------------------------------------------------------
> USER           ||
>                || communication using NETLINK
>                ||  ______________________________________________
>                || |                                              |
>         ksmbd.mountd <<= DCE/RPC(srvsvc, wkssvc, samr, lsarpc)   |
>                ^  |  <<= configure shares setting, user accounts |
>                |  |______________________________________________|
>                |
>                |------ smb.conf(config file)
>                |
>                |------ ksmbdpwd.db(user account/password file)
>                             ^
>   ksmbd.adduser ---------------|
> 
> The subset of performance related operations(open/read/write/close etc.) belong
> in kernelspace(ksmbd) and the other subset which belong to operations(DCE/RPC,
> user account/share database) which are not really related with performance are
> handled in userspace(ksmbd.mountd).
> 
> When the ksmbd.mountd is started, It starts up a forker thread at initialization
> time and opens 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.

Judging from the diagram above, all those threads are kernel threads, is
that right?  So a kernel thread gets each call first, then uses netlink
to get help from ksmbd.mountd if necessary, is that right?

--b.