2020-04-27 21:16:59 +00:00
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.. SPDX-License-Identifier: GPL-2.0
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===========================================
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2019-07-16 22:04:50 +00:00
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Mounting root file system via SMB (cifs.ko)
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===========================================
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Written 2019 by Paulo Alcantara <palcantara@suse.de>
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2020-04-27 21:16:59 +00:00
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2019-07-16 22:04:50 +00:00
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Written 2019 by Aurelien Aptel <aaptel@suse.com>
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The CONFIG_CIFS_ROOT option enables experimental root file system
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support over the SMB protocol via cifs.ko.
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It introduces a new kernel command-line option called 'cifsroot='
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which will tell the kernel to mount the root file system over the
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network by utilizing SMB or CIFS protocol.
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In order to mount, the network stack will also need to be set up by
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using 'ip=' config option. For more details, see
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2020-02-12 18:13:32 +00:00
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Documentation/admin-guide/nfs/nfsroot.rst.
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2019-07-16 22:04:50 +00:00
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A CIFS root mount currently requires the use of SMB1+UNIX Extensions
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which is only supported by the Samba server. SMB1 is the older
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deprecated version of the protocol but it has been extended to support
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POSIX features (See [1]). The equivalent extensions for the newer
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recommended version of the protocol (SMB3) have not been fully
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implemented yet which means SMB3 doesn't support some required POSIX
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file system objects (e.g. block devices, pipes, sockets).
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As a result, a CIFS root will default to SMB1 for now but the version
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to use can nonetheless be changed via the 'vers=' mount option. This
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default will change once the SMB3 POSIX extensions are fully
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implemented.
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Server configuration
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====================
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To enable SMB1+UNIX extensions you will need to set these global
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2020-04-27 21:16:59 +00:00
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settings in Samba smb.conf::
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2019-07-16 22:04:50 +00:00
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[global]
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server min protocol = NT1
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unix extension = yes # default
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Kernel command line
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===================
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2020-04-27 21:16:59 +00:00
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::
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root=/dev/cifs
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2019-07-16 22:04:50 +00:00
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This is just a virtual device that basically tells the kernel to mount
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the root file system via SMB protocol.
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2020-04-27 21:16:59 +00:00
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::
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cifsroot=//<server-ip>/<share>[,options]
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2019-07-16 22:04:50 +00:00
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Enables the kernel to mount the root file system via SMB that are
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located in the <server-ip> and <share> specified in this option.
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The default mount options are set in fs/cifs/cifsroot.c.
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server-ip
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IPv4 address of the server.
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share
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Path to SMB share (rootfs).
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options
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Optional mount options. For more information, see mount.cifs(8).
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Examples
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========
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2020-04-27 21:16:59 +00:00
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Export root file system as a Samba share in smb.conf file::
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2020-04-27 21:16:59 +00:00
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...
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[linux]
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path = /path/to/rootfs
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read only = no
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guest ok = yes
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force user = root
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force group = root
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browseable = yes
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writeable = yes
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admin users = root
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public = yes
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create mask = 0777
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directory mask = 0777
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...
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2019-07-16 22:04:50 +00:00
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2020-04-27 21:16:59 +00:00
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Restart smb service::
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2019-07-16 22:04:50 +00:00
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2020-04-27 21:16:59 +00:00
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# systemctl restart smb
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2019-07-16 22:04:50 +00:00
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Test it under QEMU on a kernel built with CONFIG_CIFS_ROOT and
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CONFIG_IP_PNP options enabled::
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2019-07-16 22:04:50 +00:00
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2020-04-27 21:16:59 +00:00
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# qemu-system-x86_64 -enable-kvm -cpu host -m 1024 \
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-kernel /path/to/linux/arch/x86/boot/bzImage -nographic \
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-append "root=/dev/cifs rw ip=dhcp cifsroot=//10.0.2.2/linux,username=foo,password=bar console=ttyS0 3"
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2019-07-16 22:04:50 +00:00
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1: https://wiki.samba.org/index.php/UNIX_Extensions
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