1 .. SPDX-License-Identifier: GPL-2.0
2
3 ===========================================
4 Mounting root file system via SMB (cifs.ko)
5 ===========================================
6
7 Written 2019 by Paulo Alcantara <palcantara@sus
8
9 Written 2019 by Aurelien Aptel <aaptel@suse.com
10
11 The CONFIG_CIFS_ROOT option enables experiment
12 support over the SMB protocol via cifs.ko.
13
14 It introduces a new kernel command-line option
15 which will tell the kernel to mount the root f
16 network by utilizing SMB or CIFS protocol.
17
18 In order to mount, the network stack will also
19 using 'ip=' config option. For more details, s
20 Documentation/admin-guide/nfs/nfsroot.rst.
21
22 A CIFS root mount currently requires the use o
23 which is only supported by the Samba server. S
24 deprecated version of the protocol but it has
25 POSIX features (See [1]). The equivalent exten
26 recommended version of the protocol (SMB3) hav
27 implemented yet which means SMB3 doesn't suppo
28 file system objects (e.g. block devices, pipes
29
30 As a result, a CIFS root will default to SMB1
31 to use can nonetheless be changed via the 'ver
32 default will change once the SMB3 POSIX extens
33 implemented.
34
35 Server configuration
36 ====================
37
38 To enable SMB1+UNIX extensions you will need t
39 settings in Samba smb.conf::
40
41 [global]
42 server min protocol = NT1
43 unix extension = yes # default
44
45 Kernel command line
46 ===================
47
48 ::
49
50 root=/dev/cifs
51
52 This is just a virtual device that basically t
53 the root file system via SMB protocol.
54
55 ::
56
57 cifsroot=//<server-ip>/<share>[,options]
58
59 Enables the kernel to mount the root file syst
60 located in the <server-ip> and <share> specifi
61
62 The default mount options are set in fs/smb/cl
63
64 server-ip
65 IPv4 address of the server.
66
67 share
68 Path to SMB share (rootfs).
69
70 options
71 Optional mount options. For more infor
72
73 Examples
74 ========
75
76 Export root file system as a Samba share in sm
77
78 ...
79 [linux]
80 path = /path/to/rootfs
81 read only = no
82 guest ok = yes
83 force user = root
84 force group = root
85 browseable = yes
86 writeable = yes
87 admin users = root
88 public = yes
89 create mask = 0777
90 directory mask = 0777
91 ...
92
93 Restart smb service::
94
95 # systemctl restart smb
96
97 Test it under QEMU on a kernel built with CONF
98 CONFIG_IP_PNP options enabled::
99
100 # qemu-system-x86_64 -enable-kvm -cpu host
101 -kernel /path/to/linux/arch/x86/boot/bzIma
102 -append "root=/dev/cifs rw ip=dhcp cifsroo
103
104
105 1: https://wiki.samba.org/index.php/UNIX_Exten
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